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Zhang P, Wu J, Jiang J, Zhang X, Ran Z, Jiang F, Zheng X, Wang J, Elsheikh A, Bao F. Evaluation of changes in corneal biomechanics after orthokeratology using Corvis ST. Cont Lens Anterior Eye 2024; 47:102100. [PMID: 38072740 DOI: 10.1016/j.clae.2023.102100] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2023] [Revised: 11/25/2023] [Accepted: 11/27/2023] [Indexed: 01/22/2024]
Abstract
PURPOSE To investigate the alterations in corneal biomechanical metrics induced by orthokeratology (ortho-k) using Corvis ST and to determine the factors influencing these changes. METHOD A prospective observational study was conducted to analyze various Corvis ST parameters in 32 children with low to moderate myopia who successfully underwent ortho-k lens fitting. Corneal biomechanical measurements via Corvis ST were acquired at six distinct time points: baseline (pre) and 2 h (pos2h), 6 h (pos6h), and 10 h (pos10h) following the removal of the first overnight wear ortho-k, one week (pos1w) and one month (pos1m) subsequent to the initiation of ortho-k. RESULT Significant differences were observed in Corvis ST Biomechanical parameters DAR2, IIR, CBI, and cCBI post ortho-k intervention. The integration of covariates (CCT, SimK, and bIOP) mitigated the differences in DAR2, IIR, and cCBI, but not in CBI. Initially, the stiffness parameter at first applanation, SP-A1, did not demonstrate significant variations, but after adjusting for covariates, noticeable differences over time were observed. The Stress-Strain Indeces, SSIv1 and SSIv2, did not manifest considerable changes over time, irrespective of the adjustment for covariates. No significant disparities were identified among different ortho-k lens brands. CONCLUSION Corneal biomechanics remained consistent throughout the one-month period of ortho-k lens wear. The observed changes in Corvis ST parameters subsequent ortho-k are primarily attributable to alterations in corneal pachymetry and morphology, rather than actual alterations in corneal biomechanics. The stability of corneal biomechanics post ortho-k treatment suggests the safety of this approach for adolescents from a corneal biomechanics perspective.
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Affiliation(s)
- PeiPei Zhang
- National Clinical Research Center for Ocular Diseases, Eye Hospital, WenZhou Medical University, Wenzhou 325027, China
| | - JinFang Wu
- Beijing Institute of Ophthalmology, Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing 100730, China.
| | - Jun Jiang
- National Clinical Research Center for Ocular Diseases, Eye Hospital, WenZhou Medical University, Wenzhou 325027, China
| | - XinYu Zhang
- National Clinical Research Center for Ocular Diseases, Eye Hospital, WenZhou Medical University, Wenzhou 325027, China
| | - ZiYing Ran
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
| | - Fan Jiang
- National Clinical Research Center for Ocular Diseases, Eye Hospital, WenZhou Medical University, Wenzhou 325027, China.
| | - XiaoBo Zheng
- National Clinical Research Center for Ocular Diseases, Eye Hospital, WenZhou Medical University, Wenzhou 325027, China; National Engineering Research Center of Ophthalmology and Optometry, Eye Hospital, Wenzhou Medical University, Wenzhou 325027, China; The Institute of Ocular Biomechanics, Wenzhou Medical University, Wenzhou 325027, China
| | - JunJie Wang
- National Clinical Research Center for Ocular Diseases, Eye Hospital, WenZhou Medical University, Wenzhou 325027, China; National Engineering Research Center of Ophthalmology and Optometry, Eye Hospital, Wenzhou Medical University, Wenzhou 325027, China; The Institute of Ocular Biomechanics, Wenzhou Medical University, Wenzhou 325027, China
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK; National Institute for Health Research (NIHR) Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK; Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing 100083, China
| | - FangJun Bao
- National Clinical Research Center for Ocular Diseases, Eye Hospital, WenZhou Medical University, Wenzhou 325027, China; National Engineering Research Center of Ophthalmology and Optometry, Eye Hospital, Wenzhou Medical University, Wenzhou 325027, China; The Institute of Ocular Biomechanics, Wenzhou Medical University, Wenzhou 325027, China.
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López-Muñoz A, López-Castaño I, Torres-Parejo Ú, García-Romera MC. A Corneal Biomechanical Study Measured with a Scheimpflug Dynamic Analyser in Soft Contact Lens Wearers. Life (Basel) 2023; 13:2313. [PMID: 38137914 PMCID: PMC10744429 DOI: 10.3390/life13122313] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2023] [Revised: 12/01/2023] [Accepted: 12/06/2023] [Indexed: 12/24/2023] Open
Abstract
The aim of this study was to evaluate the biomechanical changes in the cornea after wearing soft contact lenses (CLs) in healthy myopic patients measured with a Corvis ST® (CST, Oculus Optikgeräte GmbH, Wetzlar, Germany) analyser. This prospective, cross-sectional, single-centre study was performed on twenty-two Caucasian patients aged between 19 and 24 years (20.64 ± 1.21 years) range. Five device-specific biomechanical parameters, the central corneal thickness (CCT), and biomechanically corrected intraocular pressure (bIOP) were measured prior to fitting and one month after CL wear. Differences between the means of the deflection amplitude ratio (DA Ratio) and the standard deviation of the DA Ratio (SD DA Ratio) pre- and post-CL wear were found to be significant (p value = 0.002 in both cases). Significant differences were found between pre- and post-CL wear values in CCT (p value = 0.013). For all other biomechanical measures, no significant differences were observed before and after treatment. A significant association was found between changes in bIOP and classification according to changes in Int. Radius (p value = 0.047) and SSI (p value = 0.026) standard deviations. The corneal biomechanical indices provided by CST demonstrate that the fitting of soft CLs is a safe optical compensation method for the stability of corneal stiffness. No significant differences were found pre- and post-CL wear in the assessment of bIOP.
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Affiliation(s)
- Alfredo López-Muñoz
- Department of Physics of Condensed Matter, Optics Area, Vision Sciences Research Group (CIVIUS), Pharmacy School, University of Seville, 41009 Seville, Spain; (I.L.-C.); (M.-C.G.-R.)
- Research & Development Department (Miranza Virgen de Luján®), Ophthalmology Center, 41011 Seville, Spain
| | - Isabel López-Castaño
- Department of Physics of Condensed Matter, Optics Area, Vision Sciences Research Group (CIVIUS), Pharmacy School, University of Seville, 41009 Seville, Spain; (I.L.-C.); (M.-C.G.-R.)
| | - Úrsula Torres-Parejo
- Department of Statistics and Operations Research, University of Grenade, 18071 Grenade, Spain;
| | - Marta-C. García-Romera
- Department of Physics of Condensed Matter, Optics Area, Vision Sciences Research Group (CIVIUS), Pharmacy School, University of Seville, 41009 Seville, Spain; (I.L.-C.); (M.-C.G.-R.)
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Anderson C, Ntala C, Ozel A, Reuben RL, Chen Y. Computational homogenization of histological microstructures in human prostate tissue: Heterogeneity, anisotropy and tension-compression asymmetry. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2023; 39:e3758. [PMID: 37477174 PMCID: PMC10909480 DOI: 10.1002/cnm.3758] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Revised: 03/21/2023] [Accepted: 07/01/2023] [Indexed: 07/22/2023]
Abstract
Human prostatic tissue exhibits complex mechanical behaviour due to its multiphasic, heterogeneous nature, with hierarchical microstructures involving epithelial compartments, acinar lumens and stromal tissue all interconnected in complex networks. This study aims to establish a computational homogenization framework for quantifying the mechanical behaviour of prostate tissue, considering its multiphasic heterogeneous microstructures and the mechanical characteristics of tissue constituents. Representative tissue microstructure models were reconstructed from high-resolution histology images. Parametric studies on the mechanical properties of the tissue constituents, particularly the fibre-reinforced hyper-elasticity of the stromal tissue, were carried out to investigate their effects on the apparent tissue properties. These were then benchmarked against the experimental data reported in literature. Results showed significant anisotropy, both structural and mechanical, and tension-compression asymmetry of the apparent behaviours of the prostatic tissue. Strong correlation with the key microstructural indices such as area fractions of tissue constituents and the tissue fabric tensor was also observed. The correlation between the stromal tissue orientation and the principal directions of the apparent properties suggested an essential role of stromal tissue in determining the directions of anisotropy and the compression-tension asymmetry characteristics in normal human prostatic tissue. This work presented a homogenization and histology-based computational approach to characterize the apparent mechanical behaviours of human prostatic or other similar glandular tissues, with the ultimate aim of assessing how pathological conditions (e.g., prostate cancer and benign prostatic hyperplasia) could affect the tissue mechanical properties in a future study.
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Affiliation(s)
- Calum Anderson
- Institute of Mechanical, Process and Energy Engineering, School of Engineering and Physical SciencesHeriot‐Watt UniversityEdinburghUK
| | - Chara Ntala
- Department of Pathology, Western General HospitalUniversity of EdinburghEdinburghUK
| | - Ali Ozel
- Institute of Mechanical, Process and Energy Engineering, School of Engineering and Physical SciencesHeriot‐Watt UniversityEdinburghUK
| | - Robert L. Reuben
- Institute of Mechanical, Process and Energy Engineering, School of Engineering and Physical SciencesHeriot‐Watt UniversityEdinburghUK
| | - Yuhang Chen
- Institute of Mechanical, Process and Energy Engineering, School of Engineering and Physical SciencesHeriot‐Watt UniversityEdinburghUK
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Zhao GP, Zhai HT, Xiang HZ, Wu LM, Chen QO, Chen C, Zhou M. Biomechanical study of cornea response under orthokeratology lens therapy: A finite element analysis. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2023; 39:e3691. [PMID: 36799066 DOI: 10.1002/cnm.3691] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2022] [Accepted: 02/07/2023] [Indexed: 06/18/2023]
Abstract
Orthokeratology (OK) is becoming a mainstream modality for myopia correction and control, but its underlying mechanism is not yet fully understood. In this study, the biomechanical response of cornea under the OK lens was investigated to further understand the mechanism of OK therapy. Numerical models of the cornea and OK lens with different corneal refractive powers and myopia degrees were established to analyze features and differences of the spatial displacement and stress distribution in different areas of the anterior corneal surface by finite element method. Displacement distributions on the anterior cornea surface with refractive powers of 39.5, 43, 46 D, and myopia degrees of -1.0, -3.0, -6.0 D demonstrate similar deformation trends and nearly rotationally symmetrical attributes of different corneal parameters. Displacement of mid-peripheral cornea was significantly high compared with that of the central and peripheral cornea, peaking at ~2.4 mm off the corneal apex. The stress increased with the increase in myopia degrees and was significantly large for the myopia degrees of -6.0 D at S1; the stress at S2 and S6 was low and stable and did not differ much at S3; the stress at S4 and S5, however, was extremely high. In summary, simulation result of orthokeratology can effectively evaluate the performance of OK lens and it properly associates with the differential map of the corneal topography. The base curve of the OK lens may also play a role in mid-peripheral corneal steepening. The design around the OK lens' alignment curve needs to be optimized.
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Affiliation(s)
- Gai-Ping Zhao
- School of Health Science and Engineering, University of Shanghai for Science and Technology, Shanghai, China
| | - Hai-Tao Zhai
- School of Health Science and Engineering, University of Shanghai for Science and Technology, Shanghai, China
| | - Hua-Zhong Xiang
- School of Health Science and Engineering, University of Shanghai for Science and Technology, Shanghai, China
| | - Li-Ming Wu
- School of Health Science and Engineering, University of Shanghai for Science and Technology, Shanghai, China
| | - Qi-Ou Chen
- MicroPort Vision Power MedTech (Shanghai) Co., Ltd, Shanghai, China
| | - Chi Chen
- MicroPort Vision Power MedTech (Shanghai) Co., Ltd, Shanghai, China
| | - Meng Zhou
- MicroPort Vision Power MedTech (Shanghai) Co., Ltd, Shanghai, China
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van Setten GB. Ocular Surface Allostasis-When Homeostasis Is Lost: Challenging Coping Potential, Stress Tolerance, and Resilience. Biomolecules 2023; 13:1246. [PMID: 37627311 PMCID: PMC10452761 DOI: 10.3390/biom13081246] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Revised: 07/20/2023] [Accepted: 07/27/2023] [Indexed: 08/27/2023] Open
Abstract
The loss of ocular surface (OS) homeostasis characterizes the onset of dry eye disease. Resilience defines the ability to withstand this threat, reflecting the ability of the ocular surface to cope with and bounce back after challenging events. The coping capacity of the OS defines the ability to successfully manage cellular stress. Cellular stress, which is central to the outcome of the pathophysiology of dry eye disease, is characterized by intensity, continuity, and receptivity, which lead to the loss of homeostasis, resulting in a phase of autocatalytic dysregulation, an event that is not well-defined. To better define this event, here, we present a model providing a potential approach when homeostasis is challenged and the coping capacities have reached their limits, resulting in the stage of heterostasis, in which the dysregulated cellular stress mechanisms take over, leading to dry eye disease. The main feature of the proposed model is the concept that, prior to the initiation of the events leading to cellular stress, there is a period of intense activation of all available coping mechanisms preventing the imminent dysregulation of ocular surface homeostasis. When the remaining coping mechanisms and resilience potential have been maximally exploited and have, finally, been exceeded, there will be a transition to manifest disease with all the well-known signs and symptoms, with a shift to allostasis, reflecting the establishment of another state of balance. The intention of this review was to show that it is possibly the phase of heterostasis preceding the establishment of allostasis that offers a better chance for therapeutic intervention and optimized recovery. Once allostasis has been established, as a new steady-state of balance at a higher level of constant cell stress and inflammation, treatment may be far more difficult, and the potential for reversal is drastically decreased. Homeostasis, once lost, can possibly not be fully recovered. The processes established during heterostasis and allostasis require different approaches and treatments for their control, indicating that the current treatment options for homeostasis need to be adapted to a more-demanding situation. The loss of homeostasis necessarily implies the establishment of a new balance; here, we refer to such a state as allostasis.
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Affiliation(s)
- Gysbert-Botho van Setten
- St. Eriks Eye Hospital, 171 04 Solna, Sweden;
- Lab of DOHF and Wound Healing, Division of Eye and Vision, Department of Clinical Neuroscience, Karolinska Institutet, Eugeniavägen 12/Level 6, 171 04 Solna, Sweden
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Lan G, Twa MD, Song C, Feng J, Huang Y, Xu J, Qin J, An L, Wei X. In vivo corneal elastography: A topical review of challenges and opportunities. Comput Struct Biotechnol J 2023; 21:2664-2687. [PMID: 37181662 PMCID: PMC10173410 DOI: 10.1016/j.csbj.2023.04.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2023] [Revised: 04/07/2023] [Accepted: 04/12/2023] [Indexed: 05/16/2023] Open
Abstract
Clinical measurement of corneal biomechanics can aid in the early diagnosis, progression tracking, and treatment evaluation of ocular diseases. Over the past two decades, interdisciplinary collaborations between investigators in optical engineering, analytical biomechanical modeling, and clinical research has expanded our knowledge of corneal biomechanics. These advances have led to innovations in testing methods (ex vivo, and recently, in vivo) across multiple spatial and strain scales. However, in vivo measurement of corneal biomechanics remains a long-standing challenge and is currently an active area of research. Here, we review the existing and emerging approaches for in vivo corneal biomechanics evaluation, which include corneal applanation methods, such as ocular response analyzer (ORA) and corneal visualization Scheimpflug technology (Corvis ST), Brillouin microscopy, and elastography methods, and the emerging field of optical coherence elastography (OCE). We describe the fundamental concepts, analytical methods, and current clinical status for each of these methods. Finally, we discuss open questions for the current state of in vivo biomechanics assessment techniques and requirements for wider use that will further broaden our understanding of corneal biomechanics for the detection and management of ocular diseases, and improve the safety and efficacy of future clinical practice.
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Affiliation(s)
- Gongpu Lan
- Guangdong-Hong Kong-Macao Intelligent Micro-Nano Optoelectronic Technology Joint Laboratory, School of Physics and Optoelectronic Engineering, Foshan University, Foshan, Guangdong 528000, China
- Weiren Meditech Co., Ltd., Foshan, Guangdong 528000, China
| | - Michael D. Twa
- College of Optometry, University of Houston, Houston, TX 77204, United States
| | - Chengjin Song
- Guangdong-Hong Kong-Macao Intelligent Micro-Nano Optoelectronic Technology Joint Laboratory, School of Physics and Optoelectronic Engineering, Foshan University, Foshan, Guangdong 528000, China
| | - JinPing Feng
- Institute of Engineering and Technology, Hubei University of Science and Technology, Xianning, Hubei 437100, China
| | - Yanping Huang
- Guangdong-Hong Kong-Macao Intelligent Micro-Nano Optoelectronic Technology Joint Laboratory, School of Physics and Optoelectronic Engineering, Foshan University, Foshan, Guangdong 528000, China
- Weiren Meditech Co., Ltd., Foshan, Guangdong 528000, China
| | - Jingjiang Xu
- Guangdong-Hong Kong-Macao Intelligent Micro-Nano Optoelectronic Technology Joint Laboratory, School of Physics and Optoelectronic Engineering, Foshan University, Foshan, Guangdong 528000, China
- Weiren Meditech Co., Ltd., Foshan, Guangdong 528000, China
| | - Jia Qin
- Weiren Meditech Co., Ltd., Foshan, Guangdong 528000, China
| | - Lin An
- Weiren Meditech Co., Ltd., Foshan, Guangdong 528000, China
| | - Xunbin Wei
- Biomedical Engineering Department, Peking University, Beijing 100081, China
- International Cancer Institute, Peking University, Beijing 100191, China
- Institute of Medical Technology, Peking University Health Science Center, Beijing 100191, China
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Liu G, Rong H, Zhang P, Xue Y, Du B, Wang B, Hu J, Chen Z, Wei R. The Effect of Axial Length Elongation on Corneal Biomechanical Property. Front Bioeng Biotechnol 2021; 9:777239. [PMID: 34926423 PMCID: PMC8677453 DOI: 10.3389/fbioe.2021.777239] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Accepted: 11/15/2021] [Indexed: 01/15/2023] Open
Abstract
Background: To investigate the correlation between the corneal biomechanical parameter stress-strain index (SSI) and axial length (AL) in moderately elongated eye (MEE) and severely elongated eye (SEE). Methods: This study included 117 eyes from 117 participants. Among them, 59 (50.4%) had MEE (AL<26 mm) and 58 (49.6%) had SEE (AL≥26 mm). AL was measured using Lenstar LS-900, and central corneal thickness (CCT) and anterior chamber volume (ACV) were measured using Pentacam. SSI was measured via corneal visualisation Scheimpflug technology (Corvis ST). Kolmogorov-Smirnov test, Student’s t-test, and Pearson and partial correlation analyses were used for statistical analyses. Results: The mean (±SD) SSI was 1.08 ± 0.15 in the MEE group and 0.92 ± 0.13 in the SEE group (p < 0.01). SSI was positively correlated with age (MEE: r = 0.326, p < 0.05; SEE: r = 0.298, p < 0.05) in both groups; it was negatively correlated with AL (r = −0.476, p < 0.001) in the MEE group but not in the SEE group (p > 0.05). CCT was negatively correlated with AL (r = −0.289, p < 0.05) and ACV positively correlated with AL (r = 0.444, p < 0.001) in the MEE group. Neither CCT nor ACV was correlated with AL (p > 0.05) in the SEE group. Conclusion: Corneal biomechanical parameter SSI, which represents the stiffness of corneal tissue, was lower in the SEE group than in the MEE group. When analyzed separately, SSI was negatively correlated with AL in the MEE group, but not in the SEE group, which may provide insight into different ocular growth patterns between lower myopia and higher myopia.
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Affiliation(s)
- Guihua Liu
- Tianjin Key Laboratory of Retinal Functions and Diseases, Tianjin Branch of National Clinical Research Center for Ocular Disease, Eye Institute and School of Optometry, Tianjin Medical University Eye Hospital, Tianjin, China
| | - Hua Rong
- Tianjin Key Laboratory of Retinal Functions and Diseases, Tianjin Branch of National Clinical Research Center for Ocular Disease, Eye Institute and School of Optometry, Tianjin Medical University Eye Hospital, Tianjin, China
| | - Ping Zhang
- Tianjin Key Laboratory of Retinal Functions and Diseases, Tianjin Branch of National Clinical Research Center for Ocular Disease, Eye Institute and School of Optometry, Tianjin Medical University Eye Hospital, Tianjin, China
| | - Yu Xue
- NHC Key Laboratory of Myopia, Eye Institute and Department of Ophthalmology, Eye and ENT Hospital, Fudan University, Shanghai, China.,Key Laboratory of Myopia, Shanghai Research Center of Ophthalmology and Optometry, Chinese Academy of Medical Sciences, Shanghai, China
| | - Bei Du
- Tianjin Key Laboratory of Retinal Functions and Diseases, Tianjin Branch of National Clinical Research Center for Ocular Disease, Eye Institute and School of Optometry, Tianjin Medical University Eye Hospital, Tianjin, China
| | - Biying Wang
- Tianjin Key Laboratory of Retinal Functions and Diseases, Tianjin Branch of National Clinical Research Center for Ocular Disease, Eye Institute and School of Optometry, Tianjin Medical University Eye Hospital, Tianjin, China
| | - Jiamei Hu
- Tianjin Key Laboratory of Retinal Functions and Diseases, Tianjin Branch of National Clinical Research Center for Ocular Disease, Eye Institute and School of Optometry, Tianjin Medical University Eye Hospital, Tianjin, China
| | - Zhi Chen
- NHC Key Laboratory of Myopia, Eye Institute and Department of Ophthalmology, Eye and ENT Hospital, Fudan University, Shanghai, China.,Key Laboratory of Myopia, Shanghai Research Center of Ophthalmology and Optometry, Chinese Academy of Medical Sciences, Shanghai, China
| | - Ruihua Wei
- Tianjin Key Laboratory of Retinal Functions and Diseases, Tianjin Branch of National Clinical Research Center for Ocular Disease, Eye Institute and School of Optometry, Tianjin Medical University Eye Hospital, Tianjin, China
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Spiru B, Torres-Netto EA, Kling S, Hafezi F, Sekundo W. Hyperopic SMILE Versus FS-LASIK: A Biomechanical Comparison in Human Fellow Corneas. J Refract Surg 2021; 37:810-815. [PMID: 34914557 DOI: 10.3928/1081597x-20210830-02] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE To investigate the biomechanical properties of ex vivo human paired corneas after hyperopic correction via cap-based versus flap-based laser-assisted refractive surgery. METHODS In this prospective experimental study, 13 pairs of human corneas unsuitable for transplantation were equally divided into two groups. The pachymetry was performed in each eye just before the laser procedure. Corneas from the right eye were treated with small incision lenticule extraction (SMILE), whereas corneas from the left eye of the same donor were treated with femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK). All corneas were subjected to a refractive correction of +6.00 diopters (D) sphere with a 6.5-mm zone under a 120-µm cap (SMILE) or a 7-mm zone under a 110-µm flap (FS-LASIK). For two-dimensional biomechanical measurements, the corneoscleral buttons underwent two testing cycles (preconditioning stress-strain curve from 0.03 to 9.0 N and stress-relaxation at 9.0 N during 120 seconds) to analyze the elastic and viscoelastic material properties. The effective elastic modulus was calculated. Statistical analysis was performed with a confidence interval of 95%. RESULTS In stress-strain measurements, the effective elastic modulus was not significantly different (P > .311) between SMILE (13.5 ± 12.8 MPa) and FS-LASIK (7.56 ± 17.9 MPa). In stress-relaxation measurements, the remaining stress was not significantly different (P = .841) between SMILE (124 ± 20 kPa) and FS-LASIK (126 ± 21 kPa). CONCLUSIONS Unlike myopic correction, after hyperopic correction the cap-based procedure (SMILE) and the flap-based technique (FS-LASIK) may be considered equivalent in terms of biomechanical stability when measured experimentally in ex vivo human fellow eye corneas. [J Refract Surg. 2021;37(12):810-815.].
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Wu J, Fang W, Xu H, Liu X, Zhao D, Rong Q. The Biomechanical Response of the Cornea in Orthokeratology. Front Bioeng Biotechnol 2021; 9:743745. [PMID: 34708026 PMCID: PMC8542762 DOI: 10.3389/fbioe.2021.743745] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Accepted: 09/06/2021] [Indexed: 11/13/2022] Open
Abstract
Orthokeratology has been widely used to control myopia, but the mechanism is still unknown. To further investigate the underlying mechanism of corneal reshaping using orthokeratology lenses via the finite element method, numerical models with different corneal curvatures, corneal thicknesses, and myopia reduction degrees had been developed and validated to simulate the corneal response and quantify the changes in maximum stress in the central and peripheral corneal areas during orthokeratology. The influence of the factors on corneal response had been analyzed by using median quantile regression. A partial eta squared value in analysis of variance models was established to compare the effect size of these factors. The results showed central and peripheral corneal stress responses changed significantly with increased myopia reduction, corneal curvature, and corneal thickness. The target myopia reduction had the greatest effect on the central corneal stress value (partial eta square = 0.9382), followed by corneal curvature (partial eta square = 0.5650) and corneal thickness (partial eta square = 0.1975). The corneal curvature had the greatest effect on the peripheral corneal stress value (partial eta square = 0.5220), followed by myopia reduction (partial eta square = 0.2375) and corneal thickness (partial eta square = 0.1972). In summary, the biomechanical response of the cornea varies significantly with the change in corneal conditions and lens designs. Therefore, the orthokeratology lens design and the lens fitting process should be taken into consideration in clinical practice, especially for patients with high myopia and steep corneas.
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Affiliation(s)
- Jinfang Wu
- Department of Mechanics and Engineering Science, College of Engineering, Peking University, Beijing, China
| | - Wenxuan Fang
- Department of Mechanics and Engineering Science, College of Engineering, Peking University, Beijing, China
| | - Huiwen Xu
- Department of Epidemiology and Biostatistics, School of Public Health, Peking University, Beijing, China
- Medical Informatics Center, Peking University, Beijing, China
| | - Xiaode Liu
- Department of Mechanics and Engineering Science, College of Engineering, Peking University, Beijing, China
- X Lab, the Second Academy of CASIC, Beijing, China
| | - Dongliang Zhao
- School of Chemical Biology and Biotechnology, Peking University Shenzhen Graduate School, Shenzhen, China
| | - Qiguo Rong
- Department of Mechanics and Engineering Science, College of Engineering, Peking University, Beijing, China
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11
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Lopes BT, Bao F, Wang J, Liu X, Wang L, Abass A, Eliasy A, Elsheikh A. Review of in-vivo characterisation of corneal biomechanics. MEDICINE IN NOVEL TECHNOLOGY AND DEVICES 2021. [DOI: 10.1016/j.medntd.2021.100073] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
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12
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Alteration of corneal biomechanical properties in patients with dry eye disease. PLoS One 2021; 16:e0254442. [PMID: 34252118 PMCID: PMC8274861 DOI: 10.1371/journal.pone.0254442] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2021] [Accepted: 06/27/2021] [Indexed: 11/27/2022] Open
Abstract
Purpose To evaluate the association between symptoms and signs of dry eye diseases (DED) with corneal biomechanical parameters. Methods This cross-sectional study enrolled 81 participants without history of ocular hypertension, glaucoma, keratoconus, corneal edema, contact lens use, diabetes, and ocular surgery. All participants were evaluated for symptoms and signs of DED using OSDI questionnaire, tear film break-up time (TBUT), conjunctival and corneal staining (NEI grading) and Schirmer test. Corneal biomechanical parameters were obtained using Corvis ST. Mixed-effects linear regression analysis was used to determine the association between symptoms and signs of DED with corneal biomechanical parameters. Difference in corneal biomechanical parameter between participants with low (Schirmer value ≤10 mm; LT group) and normal (Schirmer value >10mm; NT group) tear production was analyzed using ANCOVA test. Results The median OSDI scores, TBUT, conjunctival and corneal staining scores as well as Schirmer test were 13±16.5 (range; 0–77), 5.3±4.2 seconds (range; 1.3–11), 0±1 (range; 0–4), 0±2 (ranges; 0–9) and 16±14 mm (range; 0–45) respectively. Regression analysis adjusted with participants’ refraction, intraocular pressure, and central corneal thickness showed that OSDI had a negative association with highest concavity radius (P = 0.02). The association between DED signs and corneal biomechanical parameters were found between conjunctival staining scores with second applanation velocity (A2V, P = 0.04), corneal staining scores with second applanation length (A2L, P = 0.01), Schirmer test with first applanation time (A1T, P = 0.04) and first applanation velocity (P = 0.01). In subgroup analysis, there was no difference in corneal biomechanical parameters between participants with low and normal tear production (P>0.05). The associations were found between OSDI with time to highest concavity (P<0.01) and highest displacement of corneal apex (HC-DA, P = 0.04), conjunctival staining scores with A2L (P = 0.01) and A2V (P<0.01) in LT group, and Schirmer test with A1T (P = 0.02) and HC-DA (P = 0.03), corneal staining scores with A2L (P<0.01) in NT group. Conclusions According to in vivo observation with Corvis ST, patients with DED showed more compliant corneas. The increase in dry eye severity was associated with the worsening of corneal biomechanics in both patients with low and normal tear production.
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Wilson A, Jones J, Marshall J. Interferometric Ex Vivo Evaluation of the Spatial Changes to Corneal Biomechanics Introduced by Topographic CXL: A Pilot Study. J Refract Surg 2021; 37:263-273. [PMID: 34038664 DOI: 10.3928/1081597x-20210203-01] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
PURPOSE To determine the efficacy of interferometry for examining the spatial changes to the corneal biomechanical response to simulated intraocular pressure (IOP) fluctuations that occur after corneal cross-linking (CXL) applied in different topographic locations. METHODS Displacement speckle pattern interferometry (DSPI) was used to measure the total anterior surface displacement of human and porcine corneas in response to pressure variations up to 1 mm Hg from a baseline pressure of 16.5 mm Hg, both before and after CXL treatment, which was applied in isolated topographic locations (10-minute riboflavin soak [VibeX-Xtra; Avedro, Inc], 8-minute ultraviolet-A exposure at 15 mW/cm2). Alterations to biomechanics were evaluated by directly comparing the responses before and after treatment for each cornea. RESULTS Before CXL, the corneal response to loading indicated spatial variability in mechanical properties. CXL treatments had a variable effect on the corneal response to loading dependent on the location of treatment, with reductions in regional displacement of up to 80% in response to a given pressure increase. CONCLUSIONS Selectively cross-linking in different topographic locations introduces position-specific changes to mechanical properties that could potentially be used to alter the refractive power of the cornea. Changes to the biomechanics of the cornea after CXL are complex and appear to vary significantly depending on treatment location and initial biomechanics. Hence, further investigations are required on a larger number of corneas to allow the development of customized treatment protocols. In this study, laser interferometry was demonstrated to be an effective and valuable tool to achieve this. [J Refract Surg. 2021;37(4):263-273.].
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Measurement of In Vivo Biomechanical Changes Attributable to Epithelial Removal in Keratoconus Using a Noncontact Tonometer. Cornea 2021; 39:946-951. [PMID: 32355111 DOI: 10.1097/ico.0000000000002344] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
PURPOSE To compare the biomechanical properties of the cornea after epithelial removal in eyes with keratoconus undergoing corneal cross-linking. METHODS Prospective interventional case series at a university hospital tertiary referral center. Corneal biomechanical properties were measured in patients with keratoconus undergoing corneal cross-linking, immediately before and after epithelial debridement by using a dynamic ultrahigh-speed Scheimpflug camera equipped with a noncontact tonometer. RESULTS The study comprised 45 eyes of 45 patients with a mean age of 19.6 ± 4.9 years (range 14-34). The cornea was found to be 23.7 ± 15.7 μm thinner after epithelial removal (P < 0.01). Corneal stiffness was reduced after epithelial removal as demonstrated by a significant decrease of parameters such as stiffness parameter A1 (12.31, P < 0.01), stiffness parameter-highest concavity (2.25, P < 0.01), A1 length (0.13 mm, P = 0.04), highest concavity radius of curvature (0.26 mm, P = 0.01), highest concavity time (0.22 ms, P = 0.04) and an increase in A1 velocity (-0.01 m/s, P = 0.01), A1 deformation amplitude (-0.03 mm, P ≤ 0.01), A1 deflection length (-0.32 mm, P < 0.01), A2 deformation amplitude (-0.03 mm, P = 0.01), and A2 deflection length (-1.00 mm, P < 0.01). There were no significant differences in biomechanical intraocular pressure (0.15 mm Hg, P = 0.78), deformation amplitude (0.03, P = 0.54), maximum inverse radius (-0.01 mm, P = 0.57), and whole eye movement length (-0.02 mm, P = 0.12). CONCLUSIONS Dynamic ultrahigh-speed Scheimpflug camera equipped with a noncontact tonometer offers an alternative method for in vivo measurements of the epithelial layer's contribution to corneal biomechanical properties. Our results suggest that corneal epithelium may play a more significant role in corneal biomechanical properties in patients with keratoconus than previously described.
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Abstract
Glaucoma is the second cause of irreversible blindness in the world. Intraocular pressure (IOP) is a recognized major risk factor for the development and progression of glaucomatous damage. Goldmann applanation tonometry (GAT) is internationally accepted as the gold standard for the measurement of IOP. The purpose of this study was to search for correlations between Goldmann tonometry and corneal mechanical properties and thickness by means of in vitro tests. IOP was measured by the Goldmann applanation tonometer (GIOP), and by a pressure transducer inserted in the anterior chamber of the eye (TIOP), at increasing pressure levels by addition of saline solution in the anterior chamber of enucleated pig eyes (n = 49). Mechanical properties were also determined by inflation tests. The GAT underestimated the real measurements made by the pressure transducer, with most common differences in the range 15–28 mmHg. The difference between the two instruments, highlighted by the Bland–Altman test, was confirmed by ANOVA, normality tests, and Mann–Whitney’s tests, both on the data arranged for infusions and for the data organized by pressure ranges. Pearson correlation tests revealed a negative correlation between (TIOP-GIOP) and both corneal stiffness and corneal thickness. In conclusion, data obtained showed a discrepancy between GIOP and TIOP more evident for softer and thinner corneas, that is very important for glaucoma detection.
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Vellara HR, Patel DV. Biomechanical properties of the keratoconic cornea: a review. Clin Exp Optom 2021; 98:31-8. [DOI: 10.1111/cxo.12211] [Citation(s) in RCA: 91] [Impact Index Per Article: 30.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Revised: 06/12/2014] [Accepted: 06/21/2014] [Indexed: 11/26/2022] Open
Affiliation(s)
- Hans R Vellara
- Department of Ophthalmology, New Zealand National Eye Centre, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand,
| | - Dipika V Patel
- Department of Ophthalmology, New Zealand National Eye Centre, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand,
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Peyman A, Ghoreishi M, Hashemi-Estabragh SS, Mirmohammadkhani M, Mohammadinia M, Pourazizi M. Corneal biomechanical properties after soft contact lens wear measured on a dynamic Scheimpflug analyzer: A before and after study. J Fr Ophtalmol 2021; 44:391-396. [PMID: 33618908 DOI: 10.1016/j.jfo.2020.06.050] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2020] [Revised: 06/02/2020] [Accepted: 06/08/2020] [Indexed: 11/16/2022]
Abstract
OBJECTIVES To evaluate the corneal biomechanics before and after daily use of contact lenses (CLs), measured by Scheimpflug-based devices. METHODS This prospective clinical study includes participants who were scheduled to use CLs daily for refractive error. The biomechanical parameters were measured by the Corneal Visualization Scheimpflug Technology (Corvis ST) before and one month after using the soft CLs. RESULTS Twenty-three subjects (46 eyes), including 16 female (76.2%) with a mean age of 28±7.29 years, were enrolled. There was no significant difference among biomechanical factors measured before and after contact lens wear (P>0.05). Using regression analysis of the biomechanical markers, we found a statistically significant association between second applanation length (A2 length) (P=0.001), highest concavity radius (HCR) (P=0.05), deflection amplitude ratio (DA_ratio) (P=0.05) and integrated radius (P<0.001) with age. Regarding spherical equivalent, we found a statistically significant association between central corneal thickness (CCT) (P=0.05), A2 length (P=0.03) and stiffness parameter at first applanation (SPA1) (P=0.02). CONCLUSIONS We did not find a significant difference in terms of corneal biomechanical parameters between baseline and month 1; but regression analyses showed a statistically significant association between A2 length, HCR, DA_ratio, integrated radius, CCT and SPA1 and certain subject characteristics.
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Affiliation(s)
- A Peyman
- Isfahan Eye Research Center, Department of Ophthalmology, Isfahan University of Medical Sciences, Feiz Hospital, Modares St., Isfahan, Iran.
| | - M Ghoreishi
- Parsian Vision Research Institute, Department of Ophthalmology, Isfahan University of Medical Sciences, Isfahan, Iran.
| | - S-S Hashemi-Estabragh
- Isfahan Eye Research Center, Department of Ophthalmology, Isfahan University of Medical Sciences, Isfahan, Iran.
| | - M Mirmohammadkhani
- Social Determinants of Health Research Center, Semnan University of Medical Sciences, Semnan, Iran And Department of Epidemiology and Biostatistics, School of Medicine, Semnan University of Medical Sciences, Semnan, Iran.
| | | | - M Pourazizi
- Isfahan Eye Research Center, Department of Ophthalmology, Isfahan University of Medical Sciences, Feiz Hospital, Modares St., Isfahan, Iran.
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Direct Evidence of Symmetry between Bilateral Human Corneas in Biomechanical Properties: A Comparison Study with Fresh Corneal Tissue. J Ophthalmol 2021. [DOI: 10.1155/2021/8891412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Purpose. To investigate the difference between the eyes from the same human with respect to the biomechanical properties of fresh corneal tissues and investigate the assumption of similarity of the corneal biomechanical properties between the eyes. Methods. Strip specimens extracted through a small incision lenticule extraction (SMILE) surgery were tested using a uniaxial tensile test. The specimens were extracted vertically. Low-strain tangent modulus (LSTM), high-strain tangent modulus (HSTM), and tensile strength () were the biomechanical parameters used in the comparison of the eyes from the same human. Results. Ninety corneal specimens from 45 persons were included in this study. The LSTM of the left and right eyes were 1.34 ± 0.52 and 1.37 ± 0.46 MPa, while the HSTM were 50.53 ± 7.51 and 49.41 ± 7.01 MPa, respectively. There was no significant difference between the eyes in terms of LSTM, HSTM, and. The LSTM and HSTM were significantly correlated with the spherical equivalent (SE) (, resp.). Conclusions. The assumption that the corneal biomechanical properties of the eyes from the same human are similar has been confirmed for the first time using fresh human corneal tissue. This finding may be useful in further biomechanical studies.
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Alvani A, Hashemi H, Pakravan M, Mahbod M, Amanzadeh K, Seyedian MA, Yaseri M, Jafarzadehpur E, Fotouhi A. Dynamic corneal biomechanics in different cell layers: in keratoconus and normal eyes. Ophthalmic Physiol Opt 2020; 41:414-423. [PMID: 33236803 DOI: 10.1111/opo.12768] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2020] [Revised: 10/17/2020] [Accepted: 10/19/2020] [Indexed: 11/28/2022]
Abstract
PURPOSE This study aimed to determine the relationship between corneal cellular structures and biomechanical deformation parameters in keratoconic (KC) and healthy eyes. METHODS In this prospective comparative study, 29 eyes of 29 KC patients were age- and gender-matched with 28 eyes of 28 healthy individuals using frequency matching. Corneal parameters examined included the density of basal epithelial cells, anterior keratocytes, posterior keratocytes and endothelial cells as assessed by in vivo corneal confocal microscopy (HRT III-RCM, Heidelberg Engineering, www.heidelbergengineering.com). Additionally, the coefficient of variation of endothelial cell size (CV) and the percentage of hexagonal endothelial cells (HEX%) were measured by specular microscopy (Konan NSP-9900, Konan Medical, www.konanmedical.com). Further, biomechanical deformation parameters were derived from Corvis Scheimpflug Technology (Corvis ST, Oculus, www.oculus.de). All cellular and biomechanical deformation parameters in KC and normal groups were compared, and the relationship between cellular and biomechanical parameters calculated. RESULTS In the KC group, the highest concavity (HC) delta arc length and maximum delta arc length were associated with endothelial cell density (Beta = -0.39, p = 0.03 and Beta = -0.60, p ˂ 0.001, respectively). Furthermore, there was a significant association between HC deflection length and HEX% (Beta = -0.67, p = 0.001). In the normal group, HC delta arc length and HC deflection length were significantly associated with endothelial cell density (Beta = 0.46, p = 0.02; and Beta = -0.51, p = 0.01, respectively). HC time, HC deformation amplitude and applanation 1 delta arc length were associated with CV (Beta = 0.50, p = 0.01; Beta = 0.27, p = 0.009; and Beta = -0.57, p = 0.002, respectively). Applanation 1 and applanation 2 deformation amplitudes were associated with HEX% (Beta = -0.49, p = 0.005; and Beta = -0.46, p = 0.02). CONCLUSIONS Biomechanical deformation parameters were significantly correlated with endothelial cell properties in both KC and normal groups, thereby indicating the importance of the integrity of endothelial cells to the biomechanical properties of both KC and normal corneas.
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Affiliation(s)
- Azam Alvani
- Department of Ophthalmology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.,Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran
| | - Hassan Hashemi
- Department of Ophthalmology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.,Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran
| | - Mohammad Pakravan
- Ophthalmic Epidemiology Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | | | - Kazem Amanzadeh
- Noor Research Center for Ophthalmic Epidemiology, Noor Eye Hospital, Tehran, Iran
| | | | - Mehdi Yaseri
- Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran
| | - Ebrahim Jafarzadehpur
- Department of Optometry, School of Rehabilitation, Iran University of Medical Sciences, Tehran, Iran
| | - Akbar Fotouhi
- Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran
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Chang SH, Zhou D, Eliasy A, Li YC, Elsheikh A. Experimental evaluation of stiffening effect induced by UVA/Riboflavin corneal cross-linking using intact porcine eye globes. PLoS One 2020; 15:e0240724. [PMID: 33147249 PMCID: PMC7641398 DOI: 10.1371/journal.pone.0240724] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2020] [Accepted: 10/02/2020] [Indexed: 11/24/2022] Open
Abstract
UVA/riboflavin corneal cross-linking (CXL) is a common used approach to treat progressive keratoconus. This study aims to investigate the alteration of corneal stiffness following CXL by mimicking the inflation of the eye under the in vivo loading conditions. Seven paired porcine eye globes were involved in the inflation test to examine the corneal behaviour. Cornea-only model was constructed using the finite element method, without considering the deformation contribution from sclera and limbus. Inverse analysis was conducted to calibrate the non-linear material behaviours in order to reproduce the inflation test. The corneal stress and strain values were then extracted from the finite element models and tangent modulus was calculated under stress level at 0.03 MPa. UVA/riboflavin cross-linked corneas displayed a significant increase in the material stiffness. At the IOP of 27.25 mmHg, the average displacements of corneal apex were 307 ± 65 μm and 437 ± 63 μm (p = 0.02) in CXL and PBS corneas, respectively. Comparisons performed on tangent modulus ratios at a stress of 0.03 MPa, the tangent modulus measured in the corneas treated with the CXL was 2.48 ± 0.69, with a 43±24% increase comparing to its PBS control. The data supported that corneal material properties can be well-described using this inflation methods following CXL. The inflation test is valuable for investigating the mechanical response of the intact human cornea within physiological IOP ranges, providing benchmarks against which the numerical developments can be translated to clinic.
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Affiliation(s)
- Shao-Hsuan Chang
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
- Department of Chemical Engineering, Feng Chia University, Taichung, Taiwan
- * E-mail: (LYC); (CSH)
| | - Dong Zhou
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
| | - Ashkan Eliasy
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
| | - Yi-Chen Li
- Department of Chemical Engineering, Feng Chia University, Taichung, Taiwan
- * E-mail: (LYC); (CSH)
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
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Rahmati SM, Razaghi R, Karimi A. Biomechanics of the keratoconic cornea: Theory, segmentation, pressure distribution, and coupled FE-optimization algorithm. J Mech Behav Biomed Mater 2020; 113:104155. [PMID: 33125958 DOI: 10.1016/j.jmbbm.2020.104155] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2020] [Revised: 10/14/2020] [Accepted: 10/21/2020] [Indexed: 10/23/2022]
Abstract
Understanding of the corneal biomechanical properties is of high interest due to its potential application in the early diagnosis of keratoconus (KC). KC by itself is a non-inflammatory eye disorder causes corneal structural and/or compositional anomalies. The biomechanically weakened cornea is no longer able to preserve the normal shape of the cornea against the intraocular pressure (IOP) and gradually starts to bulge outward, invoking a conical shape and subsequent distorted vision. The most popular way to measure the in vivo corneal biomechanical properties is the CorVis-ST, which enables to analyze the dynamic response of the cornea under a temporary air puff pressure. However, the complications, such as the lack of knowledge on the accurate air-puff pressure distribution on the cornea's surface as a function of the distance from the apex of the cornea as well as the time, hinder us to have a reliable estimation of the cornea's mechanical parameters. This study aims to establish patient-specific geometries of the healthy and KC corneas and calculate the pressure distribution on the cornea's surface as a function of both the distance from the apex of the cornea and time, and thereafter, the viscoelastic mechanical properties of both the healthy and KC corneas using a coupled finite element (FE)-optimization algorithm. To do that, the dynamic deformation response of six healthy and six KC corneas were measured via CorVis-ST. The videos of the in vivo deformation of the corneas under the applied air puff pressure were segmented using our segmentation algorithm to determine the anterior and posterior curvatures of the corneas during the dynamic movement of the cornea. The FE model of the corneas were established using the segmented data and subjected to a negative (pre-stress), positive IOP, and air puff pressure while the floating boundary conditions were applied to the two ends of the corneas' FE models. The simulation results were imported into a loop of FE-optimization algorithm and analyzed until the deformation amplitude at the apex of the cornea reaches to its minimum difference compared to the clinical data by CorVis-ST. The results revealed that the pressure distributions found in the literature as a function of the distance from the apex of the cornea and time unable to provide satisfactory results. Therefore, the pressure distributions both as a function of the distance and time were optimized using our coupled FE-optimization algorithm and employed to estimate the viscoelastic properties of the healthy and KC corneas. The mean percentage error (MPE) of 8.45% and 10.79% were found for the healthy and KC corneas compared to the clinical data of CorVis-ST, respectively. The results also revealed a significantly higher short-time shear modulus for the KC (62.33 MPa) compared to the healthy (37.45 MPa) corneas while the long-time shear modulus of both the healthy and KC corneas were almost the same (4.01 vs. 3.91 MPa). The proposed algorithm is a noninvasive technique capable of accurately estimating the viscoelastic mechanical properties of the cornea, which can contribute to understand the mechanism of KC development and improve diagnosis and intervention in KC.
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Affiliation(s)
| | - Reza Razaghi
- Research Department, Heel of Scene Ltd., Tokyo, Japan; Basir Eye Health Research Center, Tehran, Iran.
| | - Alireza Karimi
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, United States.
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Wilson A, Jones J, Tyrer JR, Marshall J. An interferometric ex vivo study of corneal biomechanics under physiologically representative loading, highlighting the role of the limbus in pressure compensation. EYE AND VISION 2020; 7:43. [PMID: 32832574 PMCID: PMC7433364 DOI: 10.1186/s40662-020-00207-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Accepted: 07/25/2020] [Indexed: 12/23/2022]
Abstract
Background The mechanical properties of the cornea are complex and regionally variable. This paper uses an original method to investigate the biomechanics of the cornea in response to hydrostatic loading over the typical physiological range of intra-ocular pressure (IOP) fluctuations thereby increasing understanding of clinically relevant corneal biomechanical properties and their contributions to the refractive properties of the cornea. Methods Displacement speckle pattern interferometry (DSPI) was used to measure the total surface displacement of 40 porcine and 6 human corneal-scleral specimens in response to pressure variations up to 1 mmHg from a baseline of 16.5 mmHg. All specimens were mounted in a modified artificial anterior chamber (AAC) and loaded hydrostatically. Areas of high strain in response to loading were identified by comparing the displacements across different regions. Results The nature of the response of the corneal surface to loading demonstrated high regional topographic variation. Mechanical properties were shown to be asymmetrical, and deformation of the limbal and pre-limbal regions dominated these responses respectively with over 90% (N-T) and 60% (S-I) of the total maximum displacement occurring in these regions indicating high-strain. In contrast, the curvature of the central cornea remained relatively unchanged merely translating in position. Conclusions The limbal and pre-limbal regions of the cornea appear to be fundamental to the absorption of small pressure fluctuations facilitating the curvature of the central cornea to remain relatively unchanged. The differential mechanical properties of this region could have important implications for the application of corneal surgery and corneal crosslinking, warranting further investigation.
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Affiliation(s)
- Abby Wilson
- Wolfson School of Mechanical, Manufacturing and Electrical Engineering, Loughborough University, Loughborough, UK
| | - John Jones
- Laser Optical Engineering Ltd., Derbyshire, UK
| | - John R Tyrer
- Wolfson School of Mechanical, Manufacturing and Electrical Engineering, Loughborough University, Loughborough, UK.,Laser Optical Engineering Ltd., Derbyshire, UK
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Aytekin E, Öztürk N, Vural İ, Polat HK, Çakmak HB, Çalış S, Pehlivan SB. Design of ocular drug delivery platforms and in vitro - in vivo evaluation of riboflavin to the cornea by non-interventional (epi-on) technique for keratoconus treatment. J Control Release 2020; 324:238-249. [PMID: 32413453 DOI: 10.1016/j.jconrel.2020.05.017] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Revised: 05/08/2020] [Accepted: 05/10/2020] [Indexed: 10/24/2022]
Abstract
AIM Keratoconus is a common and progressive eye disease characterized by thinning and tapering of the cornea. This degenerative eye disease is currently treated in the clinic with an interventional technique ("epi-off") that can cause serious side effects as a result of the surgical procedure. The aim of this project is to design innovative formulations for the development of a riboflavin-containing medicinal product to develop a non-invasive ("epi-on") keratoconus treatment as an alternative to current treatment modalities. METHODS Nanostructured lipid carriers (NLCs) were successfully loaded with either riboflavin base of riboflavin-5-phosphate sodium and designed with either Stearylamine (positive charge) or Trancutol P (permeation enhancer). In vitro characterization studies, cytotoxicity and permeability studies were performed. Selected formulations and commercial preparations were applied and compared in ex-vivo corneal drug accumulation and transition studies. Furthermore, in vivo studies were performed to assess drug accumulation in the rat cornea and the corneal stability after NLC treatment was investigated via a biomechanical study on isolated rabbit corneas. RESULTS Both in vitro and ex-vivo as well as in vivo data showed that from the prepared NLC formulations, the most effective formulation was riboflavin-5-phosphate sodium containing NLC with Transcutol P as permeation enhancer. It possessed the highest drug loading content, low accumulation in the cornea but high permeability through the cornea as well as the highest functional performance in corneal crosslinking. CONCLUSION Topical application of riboflavin-5-phosphate sodium loaded NLC systems designed with permeation enhancer Transcutol P may act as a potential alternative for non-invasive keratoconus treatments.
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Affiliation(s)
- Eren Aytekin
- Department of Pharmaceutical Technology, Faculty of Pharmacy, Hacettepe University, 06100 Ankara, Turkey
| | - Naile Öztürk
- Department of Pharmaceutical Technology, Faculty of Pharmacy, Inonu University, 44280 Malatya, Turkey
| | - İmran Vural
- Department of Pharmaceutical Technology, Faculty of Pharmacy, Hacettepe University, 06100 Ankara, Turkey
| | - H Kerem Polat
- Department of Pharmaceutical Technology, Faculty of Pharmacy, Hacettepe University, 06100 Ankara, Turkey
| | - Hasan Basri Çakmak
- Department of Ophthalmology, Faculty of Medicine, Hitit University, 19030 Çorum, Turkey
| | - Sema Çalış
- Department of Pharmaceutical Technology, Faculty of Pharmacy, Hacettepe University, 06100 Ankara, Turkey
| | - Sibel Bozdağ Pehlivan
- Department of Pharmaceutical Technology, Faculty of Pharmacy, Hacettepe University, 06100 Ankara, Turkey.
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Kling S, Khodadadi H, Goksel O. Optical Coherence Elastography-Based Corneal Strain Imaging During Low-Amplitude Intraocular Pressure Modulation. Front Bioeng Biotechnol 2020; 7:453. [PMID: 32083064 PMCID: PMC7004960 DOI: 10.3389/fbioe.2019.00453] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2019] [Accepted: 12/18/2019] [Indexed: 11/15/2022] Open
Abstract
Purpose: Optical coherence elastography (OCE) is a promising technique for high-resolution strain imaging in ocular tissues. A major strain-inducing factor in the eye is intraocular pressure (IOP), with diurnal physiological fluctuations reaching up to 5 mmHg. We study herein low-amplitude IOP modulation to assess local corneal strain patterns. Methods:Ex vivo porcine eye globes were adjusted to an initial IOP of 15 mmHg and subsequently 25 mmHg. Corneal strain was induced by two subsequent pressure cycles, in which IOP was first increased and then decreased, each by a total of 5 mmHg. Two-dimensional optical coherence tomography (2D-OCT) B-scans were recorded after each loading step. Axial strain maps were obtained from magnitude and phase changes and supra-pixel displacements from cross-correlation. The strain detection sensitivity was evaluated in an isotropic material. Results: Deformations arising from a single 1-mmHg step could be resolved. The largest strain amplitudes (5.11·10−3) were observed in the posterior stroma at a low initial IOP. Strain amplitude was 1.34 times higher at 15 mmHg than at 25 mmHg (p = 0.003). Upon IOP increase, the anterior cornea was compressed, whereas the posterior cornea showed axial expansion. Both morphological images and strain maps were sensitive to postmortem time. Strains that are larger than 2.44·10−5 could be reliably measured. Conclusions: Low-amplitude IOP modulation, similar to diurnal physiological changes, induced measurable deformations in corneal tissue. Axial strain maps permit a localized comparison of the corneal biomechanical response. Small-strain OCE can likely be extended to other domains.
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Affiliation(s)
- Sabine Kling
- OPTIC Team, Computer-assisted Applications in Medicine Group, Computer Vision Laboratory, Department of Information Technology and Electrical Engineering, ETH Zurich, Zurich, Switzerland
| | - Hossein Khodadadi
- OPTIC Team, Computer-assisted Applications in Medicine Group, Computer Vision Laboratory, Department of Information Technology and Electrical Engineering, ETH Zurich, Zurich, Switzerland
| | - Orcun Goksel
- OPTIC Team, Computer-assisted Applications in Medicine Group, Computer Vision Laboratory, Department of Information Technology and Electrical Engineering, ETH Zurich, Zurich, Switzerland
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Spiru B, Torres-Netto EA, Kling S, Lazaridis A, Hafezi F, Sekundo W. Biomechanical Properties of Human Cornea Tested by Two-Dimensional Extensiometry Ex Vivo in Fellow Eyes: PRK Versus SMILE. J Refract Surg 2020; 35:501-505. [PMID: 31393988 DOI: 10.3928/1081597x-20190730-02] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Accepted: 07/30/2019] [Indexed: 11/20/2022]
Abstract
PURPOSE To investigate the biomechanical properties of the ex vivo human paired corneas after completion of photorefractive keratectomy (PRK) versus small incision lenticule extraction (SMILE) in the same donor. METHODS In this experimental study, 13 pairs of human corneas unsuitable for transplantation were equally divided into two groups. Corneal thickness was measured in each eye directly before laser refractive surgery. Corneas from the right eye were treated with PRK and corneas from the left eye with SMILE. All corneas were subjected to a refractive correction of -10.00 diopters (D) sphere and -0.75 D cylinder at 0° with a 7 mm zone, using either surface ablation (PRK) or 130 µm cap (SMILE). For two-dimensional biomechanical measurements, corneoscleral buttons underwent two testing cycles (preconditioning stress-strain curve from 0.03 to 9.0 N and stress-relaxation at 9.0 N during 120 seconds) to analyze the elastic and viscoelastic material properties. The effective elastic modulus was calculated. Statistical analysis was performed with a confidence interval of 95%. RESULTS In stress-strain measurements, the effective elastic modulus was not significantly different (P = .081) between SMILE (9.58 ± 4.26 MPa) and PRK (11.9 ± 4.90 MPa). The effect size was medium (Cohen's d = 0.58). In stress-relaxation measurements, the remaining stress was not significantly different (P = .878) between SMILE (122 ± 33 kPa) and PRK (123 ± 30 kPa). CONCLUSIONS The lenticule extraction procedure (SMILE) and the surface ablation technique (PRK) may be considered equivalent in terms of biomechanical stability when measured experimentally in ex vivo human fellow eye corneas. [J Refract Surg. 2019;35(8):501-505.].
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Chen KJ, Eliasy A, Vinciguerra R, Abass A, Lopes BT, Vinciguerra P, Ambrósio R, Roberts CJ, Elsheikh A. Development and validation of a new intraocular pressure estimate for patients with soft corneas. J Cataract Refract Surg 2019; 45:1316-1323. [DOI: 10.1016/j.jcrs.2019.04.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Revised: 03/20/2019] [Accepted: 04/01/2019] [Indexed: 11/25/2022]
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Maczynska E, Karnowski K, Szulzycki K, Malinowska M, Dolezyczek H, Cichanski A, Wojtkowski M, Kaluzny B, Grulkowski I. Assessment of the influence of viscoelasticity of cornea in animal ex vivo model using air-puff optical coherence tomography and corneal hysteresis. JOURNAL OF BIOPHOTONICS 2019; 12:e201800154. [PMID: 30239154 PMCID: PMC7065616 DOI: 10.1002/jbio.201800154] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2018] [Accepted: 09/19/2018] [Indexed: 05/29/2023]
Abstract
Application of the air-puff swept source optical coherence tomography (SS-OCT) instrument to determine the influence of viscoelasticity on the relation between overall the air-puff force and corneal apex displacement of porcine corneas ex vivo is demonstrated. Simultaneous recording of time-evolution of the tissue displacement and air pulse stimulus allows obtaining valuable information related in part to the mechanical properties of the cornea. A novel approach based on quantitative analysis of the corneal hysteresis of OCT data is presented. The corneal response to the air pulse is assessed for different well-controlled intraocular pressure (IOP) levels and for the progression of cross-linking-induced stiffness of the cornea. Micrometer resolution, fast acquisition and noncontact character of the air-puff SS-OCT measurements have potential to improve the in vivo assessment of mechanical properties of the human corneas.
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Affiliation(s)
- Ewa Maczynska
- Institute of Physics, Faculty of Physics, Astronomy and InformaticsNicolaus Copernicus UniversityTorunPoland
| | - Karol Karnowski
- Institute of Physics, Faculty of Physics, Astronomy and InformaticsNicolaus Copernicus UniversityTorunPoland
| | - Krzysztof Szulzycki
- Institute of Physics, Faculty of Physics, Astronomy and InformaticsNicolaus Copernicus UniversityTorunPoland
| | - Monika Malinowska
- Laboratory of Molecular and Systemic Neuromorphology, Department of NeurophysiologyNencki Institute of Experimental Biology, Polish Academy of SciencesWarsawPoland
| | - Hubert Dolezyczek
- Laboratory of Molecular and Systemic Neuromorphology, Department of NeurophysiologyNencki Institute of Experimental Biology, Polish Academy of SciencesWarsawPoland
| | - Artur Cichanski
- Institute of Mechanics and Machine Design, Faculty of Mechanical EngineeringUTP University of Science and TechnologyBydgoszczPoland
| | - Maciej Wojtkowski
- Institute of Physics, Faculty of Physics, Astronomy and InformaticsNicolaus Copernicus UniversityTorunPoland
- Institute of Physical ChemistryPolish Academy of SciencesWarsawPoland
| | - Bartlomiej Kaluzny
- Department of Optometry, Collegium MedicumNicolaus Copernicus UniversityBydgoszczPoland
| | - Ireneusz Grulkowski
- Institute of Physics, Faculty of Physics, Astronomy and InformaticsNicolaus Copernicus UniversityTorunPoland
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Borrego-Sanz L, Sáenz-Francés San Baldomero F, Díaz Valle D, Santos Bueso E, Sánchez Jean R, Martínez de la Casa JM, Benítez Del Castillo JM, García Feijóo J, Rodríguez Rodríguez L. Comparison of corneal biomechanical properties of patients with dry eye secondary to Sjögren's syndrome and healthy subjects. J Fr Ophtalmol 2018; 41:802-808. [PMID: 30342779 DOI: 10.1016/j.jfo.2018.02.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2017] [Revised: 01/29/2018] [Accepted: 02/19/2018] [Indexed: 11/17/2022]
Abstract
PURPOSE The goal of this study is to determine whether any difference in corneal biomechanical properties exists between Sjögren's syndrome dry eye patients and healthy subjects. METHODS Thirty-one patients diagnosed with Sjögren's syndrome and associated dry eye manifestations and 44 healthy individuals were included in the study. Ultrasonic pachymetry (UP) was used to measure central corneal thickness (CCT). Corneal biomechanical parameters were obtained using ocular response analyzer (ORA). The main parameters assessed were corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann correlated intraocular pressure (IOPg) and corneal compensated IOP (IOPcc). A Student's t-test for independent groups was performed to compare the mean of these variables between both groups. RESULTS Mean CH values in Sjögren's syndrome and healthy subject eyes were 10.1mmHg and 11.18mmHg respectively, representing a statistically significant difference (P=0.003). No other variable measured differed between cases and controls (P>0.05). Mean CRF values were 9.51mmHg and 10.37mmHg respectively, and mean CCT measured by UP in cases and controls was 527.41μm and 552.51μm respectively. CONCLUSIONS Sjögren's syndrome can influence corneal biomechanical properties, specifically CH. ORA measurements should be considered of interest in the evaluation of Sjögren syndrome subjects.
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Affiliation(s)
- L Borrego-Sanz
- Department of Ophthalmology, Instituto de Investigación Sanitaria del Hospital Clínico San Carlos (IdISSC), Universidad Complutense de Madrid, Madrid, Spain.
| | - F Sáenz-Francés San Baldomero
- Department of Ophthalmology, Instituto de Investigación Sanitaria del Hospital Clínico San Carlos (IdISSC), Universidad Complutense de Madrid, Madrid, Spain
| | - D Díaz Valle
- Department of Ophthalmology, Instituto de Investigación Sanitaria del Hospital Clínico San Carlos (IdISSC), Universidad Complutense de Madrid, Madrid, Spain
| | - E Santos Bueso
- Department of Ophthalmology, Instituto de Investigación Sanitaria del Hospital Clínico San Carlos (IdISSC), Universidad Complutense de Madrid, Madrid, Spain
| | - R Sánchez Jean
- Department of Ophthalmology, Instituto de Investigación Sanitaria del Hospital Clínico San Carlos (IdISSC), Universidad Complutense de Madrid, Madrid, Spain
| | - J M Martínez de la Casa
- Department of Ophthalmology, Instituto de Investigación Sanitaria del Hospital Clínico San Carlos (IdISSC), Universidad Complutense de Madrid, Madrid, Spain
| | - J M Benítez Del Castillo
- Department of Ophthalmology, Instituto de Investigación Sanitaria del Hospital Clínico San Carlos (IdISSC), Universidad Complutense de Madrid, Madrid, Spain
| | - J García Feijóo
- Department of Ophthalmology, Instituto de Investigación Sanitaria del Hospital Clínico San Carlos (IdISSC), Universidad Complutense de Madrid, Madrid, Spain
| | - L Rodríguez Rodríguez
- Department of Rheumatology, Instituto de Investigación Sanitaria del Hospital Clínico San Carlos (IdISSC), Universidad Complutense de Madrid, Madrid, Spain
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Spiru B, Kling S, Hafezi F, Sekundo W. Biomechanical Properties of Human Cornea Tested by Two-Dimensional Extensiometry Ex Vivo in Fellow Eyes: Femtosecond Laser-Assisted LASIK Versus SMILE. J Refract Surg 2018; 34:419-423. [PMID: 29889296 DOI: 10.3928/1081597x-20180402-05] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Accepted: 04/02/2018] [Indexed: 11/20/2022]
Abstract
PURPOSE To investigate the biomechanical properties of the ex vivo human cornea after flap-based versus cap-based laser refractive surgery in the same donor. METHODS In this experimental study, 11 pairs of human corneas unsuitable for transplantation were equally divided into two groups. Corneas from the right eye were treated with femtosecond laser-assisted LASIK (FSLASIK) and corneas from the left eye with small incision lenticule extraction (SMILE). Pachymetry was measured in each eye directly before laser refractive surgery. All corneas were subjected to a refractive correction of -10.00 diopters (D) sphere and -0.75 D cylinder at 0° with a 7-mm zone, using either a 110-μm flap (FS-LASIK) or 130-μm cap (SMILE). For two-dimensional biomechanical measurements, corneoscleral buttons underwent two testing cycles (preconditioning stress-strain curve from 0.03 to 9.0 N and stress-relaxation at 9.0 N during 120 sec) to analyze the elastic and viscoelastic material properties. The effective elastic modulus was calculated. Statistical analysis was performed with a confidence interval of 95%. RESULTS In stress-strain measurements, the effective elastic modulus was 1.47 times higher (P = .003) after SMILE (median = 8.22 [interquartile range = 4.76] MPa) compared to FS-LASIK (median = 5.59 [inter-quartile range = 2.77] MPa). The effect size was large (r = 0.83). No significant differences (P = .658) were observed among stress-relaxation measurements, with a mean remaining stress of 181 ± 31 kPa after SMILE and 177 ± 26 kPa after FS-LASIK after relaxation. CONCLUSIONS Compared to a flap-based procedure such as FS-LASIK, the SMILE technique can be considered superior in terms of biomechanical stability, when measured experimentally in ex vivo human fellow eye corneas. [J Refract Surg. 2018;34(6):419-423.].
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Ma J, Wang Y, Wei P, Jhanji V. Biomechanics and structure of the cornea: implications and association with corneal disorders. Surv Ophthalmol 2018; 63:851-861. [PMID: 29857022 DOI: 10.1016/j.survophthal.2018.05.004] [Citation(s) in RCA: 72] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Revised: 05/17/2018] [Accepted: 05/21/2018] [Indexed: 12/14/2022]
Abstract
Recent studies have shown that alterations in corneal biomechanical properties are associated with corneal pathologies, particularly corneal ectasia. Moreover, these alterations may have implications with regard to the outcomes of therapeutic modalities and corneal refractive surgeries. We address corneal anatomy and its relevance to corneal biomechanical characteristics, as well as ocular and systemic conditions associated with changes in corneal biomechanics.
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Affiliation(s)
- Jiaonan Ma
- Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, China
| | - Yan Wang
- Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, China; Tianjin Eye Hospital, Tianjin Eye Institute, Tianjin Key Laboratory of Ophthalmology and Visual Science, Naikai University, Tianjin Medical University, Tianjin, China.
| | - Pinghui Wei
- Tianjin Eye Hospital, Tianjin Eye Institute, Tianjin Key Laboratory of Ophthalmology and Visual Science, Naikai University, Tianjin Medical University, Tianjin, China
| | - Vishal Jhanji
- UPMC Eye Center, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
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Bao F, Wang J, Cao S, Liao N, Shu B, Zhao Y, Li Y, Zheng X, Huang J, Chen S, Wang Q, Elsheikh A. Development and clinical verification of numerical simulation for laser in situ keratomileusis. J Mech Behav Biomed Mater 2018; 83:126-134. [PMID: 29704827 DOI: 10.1016/j.jmbbm.2018.04.016] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2017] [Revised: 04/12/2018] [Accepted: 04/17/2018] [Indexed: 10/17/2022]
Abstract
To develop and validate numerical models of the laser in situ keratomileusis (LASIK) procedure through considering its effect on corneal biomechanical behavior. 3D finite element models of the human eye were developed to simulate LASIK. The models' predictions of post-operative corneal elevation, corneal refractive power with vector decomposition (M-c-pos, J0-c-pos, J45-c-pos) and refractive error correction (M-rec, J0-rec, J45-rec) were compared against clinical data obtained for 28 eyes of 28 patients. A parallel exercise was conducted to estimate the post-operative corneal shape using a shape subtraction method (SSM) - which does not consider the effects of LASIK on corneal mechanical behavior - and the results are compared with the finite element method (FEM). A significant decrease in elevation differences between FEM predictions and clinical data was found compared with the differences between SSM results and clinical data (p = 0.000). In addition, there were no significant differences in post-operative equivalent sperical corneal refractive power between FEM results and corresponding clinical data (M-c-pos: p = 0.501), while SSM showed significant differences with clinical data (M-c-pos: p = 0.000). Further, FEM achieved a predicted value of M-c-pos within ± 1.00D accuracy in 100% of cases, compared with 57% achieved by the SSM. M-rec predicted by FEM was not significantly different from clinical results (p = 0.085), while SSM overestimated it (p = 0.000). The match between LASIK numerical model predictions with clinical measurements improved significantly when the procedure's effect on corneal biomechanical behavior was considered. This outcome has important implications on efforts to develop planning tools for refractive surgery.
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Affiliation(s)
- FangJun Bao
- Eye Hospital, WenZhou Medical University, Wenzhou 325027, China; The institution of ocular biomechanics, Wenzhou Medical University, Wenzhou, Zhejiang Province 325027, China
| | - JunJie Wang
- Eye Hospital, WenZhou Medical University, Wenzhou 325027, China; The institution of ocular biomechanics, Wenzhou Medical University, Wenzhou, Zhejiang Province 325027, China
| | - Si Cao
- Eye Hospital, WenZhou Medical University, Wenzhou 325027, China
| | - Na Liao
- Eye Hospital, WenZhou Medical University, Wenzhou 325027, China
| | - Bao Shu
- Eye Hospital, WenZhou Medical University, Wenzhou 325027, China
| | - YiPing Zhao
- Eye Hospital, WenZhou Medical University, Wenzhou 325027, China
| | - YiYu Li
- Eye Hospital, WenZhou Medical University, Wenzhou 325027, China
| | - XiaoBo Zheng
- Eye Hospital, WenZhou Medical University, Wenzhou 325027, China; The institution of ocular biomechanics, Wenzhou Medical University, Wenzhou, Zhejiang Province 325027, China
| | - JinHai Huang
- Eye Hospital, WenZhou Medical University, Wenzhou 325027, China
| | - ShiHao Chen
- Eye Hospital, WenZhou Medical University, Wenzhou 325027, China.
| | - QinMei Wang
- Eye Hospital, WenZhou Medical University, Wenzhou 325027, China; The institution of ocular biomechanics, Wenzhou Medical University, Wenzhou, Zhejiang Province 325027, China.
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK; National Institute for Health Research (NIHR) Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK
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Fernández J, Rodríguez-Vallejo M, Martínez J, Tauste A, Piñero DP. Corneal biomechanics after laser refractive surgery: Unmasking differences between techniques. J Cataract Refract Surg 2018; 44:390-398. [PMID: 29615281 DOI: 10.1016/j.jcrs.2017.10.054] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2017] [Revised: 10/02/2017] [Accepted: 10/03/2017] [Indexed: 10/17/2022]
Abstract
The hypothesis that small-incision lenticule extraction provides better preservation of corneal biomechanics than previous laser refractive techniques has led to a growth in the interest in clinical and experimental research in this field. This hypothesis is based on the fact that corneal layers with greater stiffness are preserved with this new technique. However, this hypothesis is controversial because clinical research has shown a great disparity in the outcomes. In this review, we performed an in-depth analysis of the factors that might affect corneal biomechanics in laser refractive surgery procedures from a macrostructural to a microstructural viewpoint. New advances in algorithms with current devices or the introduction of new devices might help unmask the possible advantages of small-incision lenticule extraction in corneal biomechanics.
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Affiliation(s)
- Joaquín Fernández
- From the Department of Ophthalmology (Qvision) (Fernández, Rodríguez-Vallejo, Martínez, Tauste), Vithas Virgen del Mar Hospital and the Department of Ophthalmology (Fernández, Piñero), Torrecárdenas Hospital Complex, Almería, and the Department of Optics, Pharmacology and Anatomy (Piñero), University of Alicante, and the Department of Ophthalmology (Piñero), Vithas Medimar International Hospital, Alicante, Spain
| | - Manuel Rodríguez-Vallejo
- From the Department of Ophthalmology (Qvision) (Fernández, Rodríguez-Vallejo, Martínez, Tauste), Vithas Virgen del Mar Hospital and the Department of Ophthalmology (Fernández, Piñero), Torrecárdenas Hospital Complex, Almería, and the Department of Optics, Pharmacology and Anatomy (Piñero), University of Alicante, and the Department of Ophthalmology (Piñero), Vithas Medimar International Hospital, Alicante, Spain.
| | - Javier Martínez
- From the Department of Ophthalmology (Qvision) (Fernández, Rodríguez-Vallejo, Martínez, Tauste), Vithas Virgen del Mar Hospital and the Department of Ophthalmology (Fernández, Piñero), Torrecárdenas Hospital Complex, Almería, and the Department of Optics, Pharmacology and Anatomy (Piñero), University of Alicante, and the Department of Ophthalmology (Piñero), Vithas Medimar International Hospital, Alicante, Spain
| | - Ana Tauste
- From the Department of Ophthalmology (Qvision) (Fernández, Rodríguez-Vallejo, Martínez, Tauste), Vithas Virgen del Mar Hospital and the Department of Ophthalmology (Fernández, Piñero), Torrecárdenas Hospital Complex, Almería, and the Department of Optics, Pharmacology and Anatomy (Piñero), University of Alicante, and the Department of Ophthalmology (Piñero), Vithas Medimar International Hospital, Alicante, Spain
| | - David P Piñero
- From the Department of Ophthalmology (Qvision) (Fernández, Rodríguez-Vallejo, Martínez, Tauste), Vithas Virgen del Mar Hospital and the Department of Ophthalmology (Fernández, Piñero), Torrecárdenas Hospital Complex, Almería, and the Department of Optics, Pharmacology and Anatomy (Piñero), University of Alicante, and the Department of Ophthalmology (Piñero), Vithas Medimar International Hospital, Alicante, Spain
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Template-based methodology for the simulation of intracorneal segment ring implantation in human corneas. Biomech Model Mechanobiol 2018; 17:923-938. [PMID: 29564655 DOI: 10.1007/s10237-018-1013-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Accepted: 03/12/2018] [Indexed: 10/17/2022]
Abstract
Keratoconus is an idiopathic, non-inflammatory and degenerative corneal disease characterised by a loss of the organisation in the corneal collagen fibrils. As a result, keratoconic corneas present a localised thinning and conical protrusion with irregular astigmatism and high myopia that worsen visual acuity. Intracorneal ring segments (ICRSs) are used in clinic to regularise the corneal surface and to prevent the disease from progressing. Unfortunately, the post-surgical effect of the ICRS is not explicitly accounted beforehand. Traditional treatments rely on population-based nomograms and the experience of the surgeon. In this vein, in silico models could be a clinical aid tool for clinicians to plan the intervention, or to test the post-surgical impact of different clinical scenarios. A semi-automatic computational methodology is presented in order to simulate the ICRS surgical operation and to predict the post-surgical optical outcomes. For the sake of simplicity, circular cross section rings, average corneas and an isotropic hyperelastic material are used. To determine whether the model behaves physiologically and to carry out a sensitivity analysis, a [Formula: see text] full-factorial analysis is carried out. In particular, how the stromal depth insertion, horizontal distance of ring insertion (hDRI) and diameter of the ring's cross section ([Formula: see text]) are impacting in the spherical and cylindrical power of the cornea is analysed. Afterwards, the kinematics, mechanics and optics of keratoconic corneas after the ICRS insertion are analysed. Based on the parametric study, we can conclude that our model follows clinical trends previously reported. In particular and although there is an improvement in defocus, all corneas presented a change in their optical aberrations. The stromal depth insertion is the parameter that affects the corneal optics the most, whereas hDRI and [Formula: see text] are less important. Not only that, but it is almost impossible to achieve an optimal trade-off between spherical and cylindrical correction. Regarding the mechanical behaviour, inserting the rings at 65% depth or above will cause the cornea to slightly bend. This abnormal stress distribution greatly distorts the corneal optics and, more importantly, could be the cause of clinical problems such as corneal extrusion. Not only that, but our model also supports that rings are acting as restraint elements which relax the stresses of the corneal stroma in the cone of the disease. However, depending on the exact spatial location of the keratoconus, the insertion of rings could promote its evolution instead of preventing it. ICRS inserted deeper will prevent keratoconus in the posterior stroma from growing (relaxation of posterior surface), but will promote its growing if they are located in the anterior surface (increment of stress). In conclusion, the methodology proposed is suitable for simulating long-term mechanical and optical effects of ICRS insertion.
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Vinciguerra R, Elsheikh A, Roberts CJ, Ambrósio R, Kang DSY, Lopes BT, Morenghi E, Azzolini C, Vinciguerra P. Influence of Pachymetry and Intraocular Pressure on Dynamic Corneal Response Parameters in Healthy Patients. J Refract Surg 2017; 32:550-61. [PMID: 27505316 DOI: 10.3928/1081597x-20160524-01] [Citation(s) in RCA: 139] [Impact Index Per Article: 19.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2016] [Accepted: 04/14/2016] [Indexed: 01/02/2023]
Abstract
PURPOSE To evaluate the influence of pachymetry, age, and intraocular pressure in normal patients and to provide normative values for all dynamic corneal response parameters (DCRs) provided by dynamic Scheimpflug analysis. METHODS Seven hundred five healthy patients were included in this multicenter retrospective study. The biomechanical response data were analyzed to obtain normative values with their dependence on corrected and clinically validated intraocular pressure estimates developed using the finite element method (bIOP), central corneal thickness (CCT), and age, and to evaluate the influence of bIOP, CCT, and age. RESULTS The results showed that all DCRs were correlated with bIOP except deflection amplitude (DefA) ratio, highest concavity (HC) radius, and inverse concave radius. The analysis of the relationship of DCRs with CCT indicated that HC radius, inverse concave radius, deformation amplitude (DA) ratio, and DefA ratio were correlated with CCT (rho values of 0.343, -0.407, -0.444, and -0.406, respectively). The age group subanalysis revealed that primarily whole eye movement followed by DA ratio and inverse concave radius were the parameters that were most influenced by age. Finally, custom software was created to compare normative values to imported examinations. CONCLUSIONS HC radius, inverse concave radius, DA ratio, and DefA ratio were shown to be suitable parameters to evaluate in vivo corneal biomechanics due to their independence from IOP and their correlation with pachymetry and age. The creation of normative values allows the interpretation of an abnormal examination without the need to match every case with another normal patient matched for CCT and IOP. [J Refract Surg. 2016;32(8):550-561.].
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Long Q, Wang JY, Xu D, Li Y. Comparison of corneal biomechanics in Sjögren's syndrome and non-Sjögren's syndrome dry eyes by Scheimpflug based device. Int J Ophthalmol 2017; 10:711-716. [PMID: 28546925 DOI: 10.18240/ijo.2017.05.08] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Accepted: 12/29/2016] [Indexed: 11/23/2022] Open
Abstract
AIM To compare the corneal biomechanics of Sjögren's syndrome (SS) and non-SS dry eyes with Corneal Visualization Scheimpflug Technology (CorVis ST). METHODS Corneal biomechanics and tear film parameters, namely the Schirmer I test value, tear film break-up time (TBUT) and corneal staining score (CSS) were detected in 34 eyes of 34 dry eye patients with SS (SSDE group) and 34 dry eye subjects without SS (NSSDE group) using CorVis ST. The differences of the above parameters between the two groups were examined, and the relationship between corneal biomechanics and tear film parameters were observed. RESULTS The differences in age, sex, intraocular pressure (IOP) and central corneal thickness (CCT) were not significant between the two groups (P>0.05). The tear film parameters had significant differences between the SSDE group and NSSDE group (all P<0.05). Patients in the SSDE group had significantly lower A1-time and HC-time, but higher DA (P=0.01, 0.02, and 0.02, respectively) compared with the NSSDE group. In the SSDE group, DA was negatively correlated with TBUT (rho=-0.38, P=0.03); HC-time was negatively correlated with CSS (rho=-0.43, P=0.02). In the NSSDE group, HC-time was again negatively correlated with CSS (rho=-0.39, P=0.02). CONCLUSION There are differences in corneal biomechanical properties between SSDE and NSSDE. The cornea of SSDE tends to show less "stiffness", as seen by a significantly shorter A1-time and HC-time, but larger DA, compared with the cornea of NSSDE. Biomechanical parameters can be influenced by different tear film parameters in both groups.
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Affiliation(s)
- Qin Long
- Department of Ophthalmology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, China
| | - Jing-Yi Wang
- Department of Ophthalmology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, China
| | - Dong Xu
- Department of Rheumatology and Clinical Immunology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, China
| | - Ying Li
- Department of Ophthalmology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, China
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Kling S, Hafezi F. Corneal biomechanics - a review. Ophthalmic Physiol Opt 2017; 37:240-252. [PMID: 28125860 DOI: 10.1111/opo.12345] [Citation(s) in RCA: 95] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Accepted: 11/15/2016] [Indexed: 12/01/2022]
Abstract
PURPOSE In recent years, the interest in corneal biomechanics has strongly increased. The material properties of the cornea determine its shape and therefore play an important role in corneal ectasia and related pathologies. This review addresses the molecular origin of biomechanical properties, models for their description, methods for their characterisation, techniques for their modification, and computational simulation approaches. RECENT FINDINGS Recent research has focused on developing non-contact techniques to measure the biomechanical properties in vivo, on determining structural and molecular abnormalities in pathological corneas, on developing and optimising techniques to reinforce the corneal tissue and on the computational simulation of surgical interventions. SUMMARY A better understanding of corneal biomechanics will help to improve current refractive surgeries, allow an earlier diagnosis of ectatic disorders and a better quantification of treatments aiming at reinforcing the corneal tissue.
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Affiliation(s)
- Sabine Kling
- CABMM, University of Zurich, Zurich, Switzerland
| | - Farhad Hafezi
- CABMM, University of Zurich, Zurich, Switzerland.,ELZA Institute AG Dietikon, Zurich, Switzerland.,USC Roski Eye Institute - Keck School of Medicine, Los Angeles, USA.,Ophthalmology, University of Geneva, Geneva, Switzerland
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Koprowski R, Kasprzak H, Wróbel Z. New automatic method for analysis and correction of image data from the Corvis tonometer. COMPUTER METHODS IN BIOMECHANICS AND BIOMEDICAL ENGINEERING: IMAGING & VISUALIZATION 2017. [DOI: 10.1080/21681163.2014.959137] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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KHAN SALMANN, SHIAKOLAS PANOSS. TO STUDY THE EFFECTS OF INTRASTROMAL CORNEAL RING GEOMETRY AND SURGICAL CONDITIONS ON THE POSTSURGICAL OUTCOMES THROUGH FINITE ELEMENT ANALYSIS. J MECH MED BIOL 2016. [DOI: 10.1142/s0219519416501013] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Intrastromal corneal ring (ICR) is a transparent circular implant inserted in the cornea to provide structural support in an attempt to alleviate preexisting refractive errors. This is a surgical procedure whose success depends on control parameters such as, ICR geometry which includes ICR thickness and diameter, and surgical conditions which includes ICR implantation depth and diameter of corneal pocket. This research utilizes finite element (FE) analysis techniques to develop a high fidelity and computationally efficient three-dimensional axisymmetric cornea model to study the relative effects of ICR implant geometry and surgical conditions on the postsurgical shape of the cornea utilizing corneal apical displacement results. The FE analysis results indicate that ICR implantation reduces myopia, and the amount of myopic rectification is dependent on the control parameters which include ICR geometry and surgical conditions. The results show that an increase in ICR thickness leads to an increase in myopic rectification, whereas an increase in ICR radius leads to a decrease in myopic rectification. ICR implantation depth analysis results suggest that corneal depth of 40–75% provides steady myopic rectification. Corneal pocket diameter analysis revealed that smaller corneal pockets lead to increase in myopic rectification. Overall, the FE model results are in qualitative agreement with published clinical studies. Finally, the combined impact of the control parameters on myopic rectification was studied by conducting a sensitivity analysis and an equation relating myopic rectification with control parameters was developed utilizing simple linear regression analysis.
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Affiliation(s)
- SALMAN N. KHAN
- Micro Manufacturing Medical Automation and Robotics Laboratory, Department of Mechanical Engineering, The University of Texas at Arlington, Arlington, TX 76010, USA
| | - PANOS S. SHIAKOLAS
- Micro Manufacturing Medical Automation and Robotics Laboratory, Department of Mechanical Engineering, The University of Texas at Arlington, Arlington, TX 76010, USA
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Khan SN, Shiakolas PS. Finite Element Analysis of Descemet's Stripping Automated Endothelial Keratoplasty (DSAEK) Surgery Allograft to Predict Endothelial Cell Loss. Curr Eye Res 2016; 42:32-40. [PMID: 27249218 DOI: 10.3109/02713683.2016.1151052] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
PURPOSE To develop high fidelity finite element (FE) models of the Descemet's stripping automated endothelial keratoplasty (DSAEK) allograft to estimate the stress distributions generated on the allograft during its deformed state in popular allograft insertion configurations and qualitatively correlate the stress distributions to postsurgical endothelial cell (EC) loss. MATERIALS AND METHODS Corneal allograft simulation was performed using ANSYS (Canonsburg, PA, USA) utilizing isotropic nonlinear hyperelastic corneal material properties to evaluate the stress distributions generated on the DSAEK allograft during popular allograft insertion configurations, namely forceps, taco, and double-coil insertion configurations. The gathered FE simulation results were qualitatively compared with published clinical studies to verify the simulation results. RESULTS The FE simulation results demonstrate that high stress regions predicted by FE model results correctly predict the areas of postsurgical EC loss as published in the studies available in open literature. The FE simulation stress magnitude results suggest that highest EC loss due to mechanical bending trauma occurs in double-coil configuration followed by forceps and then taco configuration. CONCLUSIONS The results of the presented FE simulation study highlight that allograft regions with high stress distribution demonstrate postsurgical EC loss in clinical studies. The modeling procedures presented in this research can be utilized to develop novel surgical devices/techniques that can modulate the postsurgical EC loss due to mechanical bending trauma and facilitate allograft unfolding inside the AC, thereby improving the results of the DSAEK surgical procedure.
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Affiliation(s)
- Salman N Khan
- a Micro Manufacturing Medical Automation and Robotics Laboratory, Department of Mechanical and Aerospace Engineering , The University of Texas at Arlington , Arlington , Texas , USA
| | - Panos S Shiakolas
- a Micro Manufacturing Medical Automation and Robotics Laboratory, Department of Mechanical and Aerospace Engineering , The University of Texas at Arlington , Arlington , Texas , USA
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Comparison of Corneal Biomechanical Characteristics After Surface Ablation Refractive Surgery and Novel Lamellar Refractive Surgery. Cornea 2016; 34:1441-6. [PMID: 26226471 DOI: 10.1097/ico.0000000000000556] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE To investigate and compare corneal biomechanical changes in the form of corneal hysteresis (CH) and corneal resistance factor (CRF) after small-incision lenticule extraction (SMILE) and laser-assisted subepithelial keratectomy (LASEK). METHODS In this retrospective observational study, patients who underwent either SMILE (36 eyes, 21 patients) or LASEK (35 eyes, 19 patients) were included. Data were collected preoperatively and at 1 and 3 months postoperatively, which included corneal topography and Ocular Response Analyzer values of CH, CRF, and intraocular pressure (IOP). Differences between both surgical groups and the relationships between variables were evaluated. RESULTS CH, CRF, Goldmann IOP, and corneal compensated IOP after surgery were significantly lower than the preoperative values (P < 0.05) in both surgical groups. Lenticule thickness (LT) correlated with ΔCRF (Δ = postoperative - preoperative value) in the SMILE group (r = -0.513, P = 0.001), but the ablation depth (AD) and ΔCRF showed no correlation in the LASEK group (r = -0.297, P = 0.083). In the SMILE group, ΔCRF/LT (-0.036 ± 0.01) and ΔCH/LT (-0.021 ± 0.01) values were significantly lower than ΔCRF/AD (-0.048 ± 0.02) and ΔCH/AD (-0.026 ± 0.02) values in the LASEK group (P < 0.05). CONCLUSIONS Both SMILE and LASEK alter corneal biomechanical strength. However, the changes induced by SMILE are more predictable than those induced by LASEK. In terms of per unit tissue removed, SMILE seems to have less effect on corneal biomechanics than LASEK, which may be due to preservation of the stiffer anterior stroma.
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Cheng X, Petsche SJ, Pinsky PM. A structural model for the in vivo human cornea including collagen-swelling interaction. J R Soc Interface 2016; 12:20150241. [PMID: 26156299 DOI: 10.1098/rsif.2015.0241] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A structural model of the in vivo cornea, which accounts for tissue swelling behaviour, for the three-dimensional organization of stromal fibres and for collagen-swelling interaction, is proposed. Modelled as a binary electrolyte gel in thermodynamic equilibrium, the stromal electrostatic free energy is based on the mean-field approximation. To account for active endothelial ionic transport in the in vivo cornea, which modulates osmotic pressure and hydration, stromal mobile ions are shown to satisfy a modified Boltzmann distribution. The elasticity of the stromal collagen network is modelled based on three-dimensional collagen orientation probability distributions for every point in the stroma obtained by synthesizing X-ray diffraction data for azimuthal angle distributions and second harmonic-generated image processing for inclination angle distributions. The model is implemented in a finite-element framework and employed to predict free and confined swelling of stroma in an ionic bath. For the in vivo cornea, the model is used to predict corneal swelling due to increasing intraocular pressure (IOP) and is adapted to model swelling in Fuchs' corneal dystrophy. The biomechanical response of the in vivo cornea to a typical LASIK surgery for myopia is analysed, including tissue fluid pressure and swelling responses. The model provides a new interpretation of the corneal active hydration control (pump-leak) mechanism based on osmotic pressure modulation. The results also illustrate the structural necessity of fibre inclination in stabilizing the corneal refractive surface with respect to changes in tissue hydration and IOP.
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Affiliation(s)
- Xi Cheng
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Steven J Petsche
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Peter M Pinsky
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
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Assessment of Corneal Biomechanical Properties by CorVis ST in Patients with Dry Eye and in Healthy Subjects. J Ophthalmol 2015; 2015:380624. [PMID: 26634151 PMCID: PMC4655069 DOI: 10.1155/2015/380624] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2015] [Revised: 09/05/2015] [Accepted: 09/10/2015] [Indexed: 12/18/2022] Open
Abstract
Purpose. To investigate corneal biomechanical properties in patients with dry eye and in healthy subjects using Corneal Visualization Scheimpflug Technology (CorVis ST). Methods. Biomechanical parameters were measured using CorVis ST in 28 eyes of 28 patients with dry eye (dry eye group) and 26 normal subjects (control group). The Schirmer I test value, tear film break-up time (TBUT), and corneal staining score (CSS) were recorded for each eye. Biomechanical properties were compared between the two groups and bivariate correlation analysis was used to assess the relationship between biomechanical parameters and dry eye signs. Results. Only one of the ten biomechanical parameters was significantly different between the two groups. Patients in the dry eye group had significantly lower highest concavity time (HC-time) (P = 0.02) than the control group. Correlation analysis showed a significant negative correlation between HC-time and CSS with marginal P value (ρ = −0.39, P = 0.04) in the dry eye group. Conclusions. The corneal biomechanical parameter of HC-time is reduced in dry eyes compared to normal eyes. There was also a very weak but significant negative correlation between HC-time and CSS in the dry eye group, indicating that ocular surface damage can give rise to a more compliant cornea in dry eyes.
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Koprowski R, Ambrósio R, Reisdorf S. Scheimpflug camera in the quantitative assessment of reproducibility of high-speed corneal deformation during intraocular pressure measurement. JOURNAL OF BIOPHOTONICS 2015; 8:968-978. [PMID: 25623926 DOI: 10.1002/jbio.201400137] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2014] [Revised: 12/19/2014] [Accepted: 12/28/2014] [Indexed: 06/04/2023]
Abstract
The paper presents an original analysis method of corneal deformation images from the ultra-high-speed Scheimpflug camera (Corvis ST tonometer). Particular attention was paid to deformation frequencies exceeding 100 Hz and their reproducibility in healthy subjects examined repeatedly. A total of 4200 images with a resolution of 200 × 576 pixels were recorded. The data derived from 3 consecutive measurements from 10 volunteers with normal corneas. A new image analysis algorithm, written in Matlab with the use of the Image Processing package, adaptive image filtering, morphological analysis methods and fast Fourier transform, was proposed. The following results were obtained: (1) reproducibility of the eyeball reaction in healthy subjects with precision of 10%, (2) corneal vibrations with a frequency of 369 ± 65 Hz (3) and amplitude of 7.86 ± 1.28 µm, (4) the phase shift within two parts of the cornea of the same subject of about 150°. The result of image sequence analysis for one subject and deformations with a corneal frequency response above 100 Hz.
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Affiliation(s)
- Robert Koprowski
- Department of Biomedical Computer Systems, University of Silesia, Faculty of Computer Science and Materials Science, Institute of Computer Science, ul. Będzińska 39, Sosnowiec, 41-200, Poland.
| | - Renato Ambrósio
- Department of Ophthalmology of the Federal University of São Paulo & Rio de Janeiro Corneal Tomography and Biomechanics Study Group of the Instituto de Olhos Renato Ambrósio, Rua Conde de Bonfim 211 / 712, Rio de Janeiro, RJ - CEP: 20520-050, Brasil
| | - Sven Reisdorf
- OCULUS Optikgeräte GmbH, Münchholzhäuser Straße 29, 35582, Wetzlar, Germany
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Ariza-Gracia MÁ, Zurita JF, Piñero DP, Rodriguez-Matas JF, Calvo B. Coupled biomechanical response of the cornea assessed by non-contact tonometry. A simulation study. PLoS One 2015; 10:e0121486. [PMID: 25780915 PMCID: PMC4364121 DOI: 10.1371/journal.pone.0121486] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2014] [Accepted: 02/02/2015] [Indexed: 11/25/2022] Open
Abstract
The mechanical response of the cornea subjected to a non-contact air-jet tonometry diagnostic test represents an interplay between its geometry, the corneal material behavior and the loading. The objective is to study this interplay to better understand and interpret the results obtained with a non-contact tonometry test. A patient-specific finite element model of a healthy eye, accounting for the load free configuration, was used. The corneal tissue was modeled as an anisotropic hyperelastic material with two preferential directions. Three different sets of parameters within the human experimental range obtained from inflation tests were considered. The influence of the IOP was studied by considering four pressure levels (10–28 mmHg) whereas the influence of corneal thickness was studied by inducing a uniform variation (300–600 microns). A Computer Fluid Dynamics (CFD) air-jet simulation determined pressure loading exerted on the anterior corneal surface. The maximum apex displacement showed a linear variation with IOP for all materials examined. On the contrary, the maximum apex displacement followed a cubic relation with corneal thickness. In addition, a significant sensitivity of the apical displacement to the corneal stiffness was also obtained. Explanation to this behavior was found in the fact that the cornea experiences bending when subjected to an air-puff loading, causing the anterior surface to work in compression whereas the posterior surface works in tension. Hence, collagen fibers located at the anterior surface do not contribute to load bearing. Non-contact tonometry devices give useful information that could be misleading since the corneal deformation is the result of the interaction between the mechanical properties, IOP, and geometry. Therefore, a non-contact tonometry test is not sufficient to evaluate their individual contribution and a complete in-vivo characterization would require more than one test to independently determine the membrane and bending corneal behavior.
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Affiliation(s)
- Miguel Á. Ariza-Gracia
- Aragón Institute of Engineering Research (I3A), University of Zaragoza, Zaragoza, Spain
- * E-mail:
| | - Jesús F. Zurita
- Department of Mechanical Engineering, Energetics and Materials, Public University of Navarra, Pamplona, Spain
| | - David P. Piñero
- Ophthalmology Department (OFTALMAR), Medimar International Hospital, Alicante, Spain
- Optics, Pharmacologist and Anatomy Department, University of Alicante, Alicante, Spain
| | | | - Begoña Calvo
- Aragón Institute of Engineering Research (I3A), University of Zaragoza, Zaragoza, Spain
- Bioengineering, Biomaterials and Nanomedicine Online Biomedical Research Center (CIBER-BBN), Zaragoza, Spain
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Frings A, Linke SJ, Bauer EL, Druchkiv V, Katz T, Steinberg J. Effects of laser in situ keratomileusis (LASIK) on corneal biomechanical measurements with the Corvis ST tonometer. Clin Ophthalmol 2015; 9:305-11. [PMID: 25709393 PMCID: PMC4334333 DOI: 10.2147/opth.s76491] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Purpose This study was initiated to evaluate biomechanical changes using the Corvis ST tonometer (CST) on the cornea after laser in situ keratomileusis (LASIK). Setting University Medical Center Hamburg-Eppendorf, Germany, and Care Vision Refractive Centers, Germany. Design Retrospective cohort study. Methods This retrospective study included 37 eyes of 37 refractive patients. All CST measurements were performed 1 day before surgery and at the 1-month follow-up examination. The LASIK procedure included mechanical flap preparation using a Moria SBK microkeratome and an Allegretto excimer laser platform. Results Statistically significant differences were observed for mean first applanation length, mean first and second deflection lengths, mean first and second deflection amplitudes, radius of curvature, and peak distance. Significant positive correlations were found between the change (Δ) of radius of curvature and manifest refraction spherical equivalent (MRSE), ablation depth, and Δintraocular pressure as well as between AD and ΔHC-time. Each diopter of myopic correction in MRSE resulted in an increase in Δradius of curvature of 0.2 mm. Conclusion Several CST parameters were statistically significantly altered by LASIK, thereby indicating that flap creation, ablation, or both, significantly change the ability of the cornea to absorb or dissipate energy.
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Affiliation(s)
- Andreas Frings
- Department of Ophthalmology, University Medical Center Hamburg-Eppendorf (UKE), Hamburg, Germany
| | - Stephan J Linke
- Department of Ophthalmology, University Medical Center Hamburg-Eppendorf (UKE), Hamburg, Germany ; Care Vision Refractive Center, Hamburg, Germany
| | - Eva L Bauer
- Department of Ophthalmology, University Medical Center Hamburg-Eppendorf (UKE), Hamburg, Germany
| | - Vasyl Druchkiv
- Department of Ophthalmology, University Medical Center Hamburg-Eppendorf (UKE), Hamburg, Germany
| | - Toam Katz
- Department of Ophthalmology, University Medical Center Hamburg-Eppendorf (UKE), Hamburg, Germany ; Care Vision Refractive Center, Hamburg, Germany
| | - Johannes Steinberg
- Department of Ophthalmology, University Medical Center Hamburg-Eppendorf (UKE), Hamburg, Germany ; Care Vision Refractive Center, Hamburg, Germany
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Koprowski R, Wilczyński S, Nowinska A, Lyssek-Boron A, Teper S, Wylegala E, Wróbel Z. Quantitative assessment of responses of the eyeball based on data from the Corvis tonometer. Comput Biol Med 2015; 58:91-100. [PMID: 25622180 DOI: 10.1016/j.compbiomed.2015.01.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2014] [Revised: 12/31/2014] [Accepted: 01/09/2015] [Indexed: 10/24/2022]
Abstract
BACKGROUND The "air-puff" tonometers, include the Corvis, are a type of device for measuring intraocular pressure and biomechanics parameters. The paper attempts to analyse this response and its relationship with other parameters measured in the Corvis tonometer. METHODS A number of 13,400 2D images were acquired from the Corvis device and analysed (32 healthy and 16 ill people). A new method has been proposed for the analysis of responses of the eyeball based on morphological transformations and contextual operations. RESULTS The proposed algorithm enables to determine responses of the eyeball to an air puff coming from the Corvis tonometer. Additionally, responses of the eyeball have been linked to some selected features of corneal deformation. The results include, among others: (1) distinguishability between the left and right eye with an error of 7%; (2) the correlation between the area under the curve in corneal deformation and the response of the eyeball -0.26; (3) the correlation between the highest concavity time and the maximum deformation amplitude of 0.4. All these features are obtained fully automatically and repetitively at a time of 3.8s per patient (Core i7 10GB RAM). DISCUSSION It is possible to measure additional parameters of the eye deformation which are not available in the original software of the Corvis tonometer. The use of the proposed methods of image analysis and processing provides results directly from the eye response measurement when measuring intraocular pressure.
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Affiliation(s)
- Robert Koprowski
- Department of Biomedical Computer Systems, University of Silesia, Faculty of Computer Science and Materials Science, Institute of Computer Science, ul. Będzińska 39, Sosnowiec 41-200, Poland.
| | - Sławomir Wilczyński
- Department of Basic Biomedical Science, School of Pharmacy, Medical University of Silesia in Katowice, ul, Kasztanowa 3, Sosnowiec 41-200, Poland
| | - Anna Nowinska
- Ophthalmology Clinic, Medical University of Silesia, District Railway Hospital in Katowice, Katowice, Poland
| | - Anita Lyssek-Boron
- Ophthalmology Clinic, Medical University of Silesia, District Railway Hospital in Katowice, Katowice, Poland
| | - Sławomir Teper
- Ophthalmology Clinic, Medical University of Silesia, District Railway Hospital in Katowice, Katowice, Poland
| | - Edward Wylegala
- Ophthalmology Clinic, Medical University of Silesia, District Railway Hospital in Katowice, Katowice, Poland
| | - Zygmunt Wróbel
- Department of Biomedical Computer Systems, University of Silesia, Faculty of Computer Science and Materials Science, Institute of Computer Science, ul. Będzińska 39, Sosnowiec 41-200, Poland
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Elsheikh A, Joda A, Abass A, Garway-Heath D. Assessment of the Ocular Response Analyzer as an Instrument for Measurement of Intraocular Pressure and Corneal Biomechanics. Curr Eye Res 2014; 40:1111-9. [PMID: 25495865 DOI: 10.3109/02713683.2014.978479] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
PURPOSE The purpose of this study is to provide better understanding of the Ocular Response Analyzer (ORA) and how reliable it is to produce intraocular pressure (IOP) measurements that are free of the effects of corneal stiffness parameters, and stiffness estimates that are independent of IOP. MATERIALS AND METHODS A numerical parametric study that closely represents the in-vivo conditions of the human eye and the ORA procedure was conducted to determine the correlation coefficient r(2) between ORA output and the values of true IOP and a number of stiffness parameters, namely corneal thickness, curvature and age. For the purpose of this exercise, the ORA output was put in the form k1P1+k2P2 where k1 and k2 were variables and P1 and P2 were ORA's measured applanation pressures. Two separate clinical datasets involving Moorfields Eye Hospital, London and the University of New South Wales, Sydney participants, respectively, were used to validate the numerical results. RESULTS The numerical study results show a strong association between (k1P1 + k2P2) and the true IOP over a wide range of k1 and k2 values apart from a narrow region approximately extending from (k1 = +2, k2 = -2) to (k1 = -2, k2 = +2). On the other hand, (k1· P1 + k2· P2) was found to have a strong association with CCT, R and age (the stiffness parameters) over the same narrow region, beyond which the association was weak. Similar trends were found with the two clinical datasets. CONCLUSIONS The results of this study show the potential of the ORA to provide reliable IOP measurements with weak dependence on the cornea's stiffness parameters and the considerably reduced reliability in producing stiffness estimates that are unaffected by IOP values.
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Affiliation(s)
- Ahmed Elsheikh
- a School of Engineering, University of Liverpool , Brownlow Hill , Liverpool , UK .,b National Institute for Health Research (NIHR) Biomedical Research Centre, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology , London , UK and
| | - Akram Joda
- a School of Engineering, University of Liverpool , Brownlow Hill , Liverpool , UK
| | - Ahmed Abass
- c Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University , Cardiff , UK
| | - David Garway-Heath
- b National Institute for Health Research (NIHR) Biomedical Research Centre, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology , London , UK and
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Piñero DP, Alcón N. Corneal biomechanics: a review. Clin Exp Optom 2014; 98:107-16. [PMID: 25470213 DOI: 10.1111/cxo.12230] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2014] [Revised: 08/12/2014] [Accepted: 08/19/2014] [Indexed: 01/19/2023] Open
Abstract
Biomechanics is often defined as 'mechanics applied to biology'. Due to the variety and complexity of the behaviour of biological structures and materials, biomechanics is better defined as the development, extension and application of mechanics for a better understanding of physiology and physiopathology and consequently for a better diagnosis and treatment of disease and injury. Different methods for the characterisation of corneal biomechanics are reviewed in detail, including those that are currently commercially available (Ocular Response Analyzer and CorVis ST). The clinical applicability of the parameters provided by these devices are discussed, especially in the fields of glaucoma, detection of ectatic disorders and orthokeratology. Likewise, other methods are also reviewed, such as Brillouin microscopy or dynamic optical coherence tomography and others with potential application to clinical practice but not validated for in vivo measurements, such as ultrasonic elastography. Advantages and disadvantages of all these techniques are described. Finally, the concept of biomechanical modelling is revised as well as the requirements for developing biomechanical models, with special emphasis on finite element modelling.
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Affiliation(s)
- David P Piñero
- Department of Ophthalmology (Oftalmar), Medimar International Hospital, Alicante, Spain; Foundation for the Visual Quality, Fundación para la Calidad Visual, Alicante, Spain; Departament of Optics, Pharmacology and Anatomy, University of Alicante, Spain
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Koprowski R. Automatic method of analysis and measurement of additional parameters of corneal deformation in the Corvis tonometer. Biomed Eng Online 2014; 13:150. [PMID: 25406740 PMCID: PMC4258810 DOI: 10.1186/1475-925x-13-150] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2014] [Accepted: 11/03/2014] [Indexed: 12/03/2022] Open
Abstract
INTRODUCTION The method for measuring intraocular pressure using the Corvis tonometer provides a sequence of images of corneal deformation. Deformations of the cornea are recorded using the ultra-high-speed Scheimpflug camera. This paper presents a new and reproducible method of analysis of corneal deformation images that allows for automatic measurements of new features, namely new three parameters unavailable in the original software. MATERIAL AND METHOD The images subjected to processing had a resolution of 200 × 576 × 140 pixels. They were acquired from the Corvis tonometer and simulation. In total 14,000 2D images were analysed. The image analysis method proposed by the author automatically detects the edge of the cornea and sclera fragments. For this purpose, new methods of image analysis and processing proposed by the author as well as those well-known, such as Canny filter, binarization, median filtering etc., have been used. The presented algorithms were implemented in Matlab (version 7.11.0.584-R2010b) with Image Processing toolbox (version 7.1-R2010b) using both known algorithms for image analysis and processing and those proposed by the author. RESULTS Owing to the proposed algorithm it is possible to determine three parameters: (1) the degree of the corneal reaction relative to the static position; (2) the corneal length changes; (3) the ratio of amplitude changes to the corneal deformation length. The corneal reaction is smaller by about 30.40% compared to its static position. The change in the corneal length during deformation is very small, approximately 1% of its original length. Parameter (3) enables to determine the applanation points with a correlation of 92% compared to the conventional method for calculating corneal flattening areas. The proposed algorithm provides reproducible results fully automatically within a few seconds/per patient using Core i7 processor. CONCLUSIONS Using the proposed algorithm, it is possible to measure new, additional parameters of corneal deformation, which are not available in the original software. The presented analysis method provides three new parameters of the corneal reaction. Detailed clinical studies based on this method will be presented in subsequent papers.
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Affiliation(s)
- Robert Koprowski
- Department of Biomedical Computer Systems, University of Silesia, Faculty of Computer Science and Materials Science, Institute of Computer Science, ul, Będzińska 39, Sosnowiec 41-200, Poland.
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