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Li J, Qin J, Lv X, Xu Y, Jiang D, Yuan M, Sun M, Zhang F. Study of corneal and retinal thicknesses at five years after FS-LASIK and SMILE for myopia. BMC Ophthalmol 2024; 24:396. [PMID: 39237938 PMCID: PMC11378561 DOI: 10.1186/s12886-024-03661-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2024] [Accepted: 08/27/2024] [Indexed: 09/07/2024] Open
Abstract
BACKGROUND This study aimed to observe corneal and retinal thicknesses at 5 years after femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) for myopia, investigate the effect of epithelial remodeling on refractive status and visual quality, and compare retinal thicknesses among fundus tessellation grades. METHODS Patients who received FS-LASIK or SMILE 5 years before were enrolled in this cross-sectional study. After 1:1 propensity score matching, each surgical group obtained 177 patients (177 eyes). Examinations including visual acuity, refraction, corneal and retinal thicknesses, corneal higher-order aberrations (HOAs), and fundus photography were performed in this visit at 5 years after surgery. The Quality of Vision (QoV) questionnaire was used to assess visual symptoms and overall satisfaction. Corneal and retinal thicknesses between groups were compared, contributing factors were analyzed, and correlations with postoperative refractive status, HOAs, QoV scores and overall satisfaction were evaluated. RESULTS The discrepancy of epithelial thickness between central and pericentral zones in FS-LASIK group was larger than that in SMILE group, which was negatively correlated with postoperative spherical equivalent (SE), positively correlated with spherical aberration (all P < 0.05), but not correlated with QoV scores and overall satisfaction (all P > 0.05) in both surgical groups. There was no statistical difference in stromal thickness and total corneal thickness (all P > 0.05). Most annuluses of epithelial and stromal thicknesse were linearly related to preoperative SE (all P < 0.05). The macular thickness, ganglion cell complex thickness, and retinal nerve fiber layer thickness exhibited comparable values between two surgical groups and four fundus tessellation grades, with no significant association observed with postoperative SE (all P > 0.05). CONCLUSION The tendency that epithelial thickness in central zone was thicker than peripheral zone was more obvious at 5 years after FS-LASIK compared to SMILE. This uneven distribution of epithelial thickness might play a role in myopic regression and the changes in HOAs, especially in patients with high myopia, but it had little effect on patients' subjective visual quality and satisfaction. Retinal thicknesses were not affected by these two surgical methods, and they did not appear to be the clinical indicators for myopic regression or fundus tessellation progression.
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Affiliation(s)
- Jiayu Li
- Beijing Tongren Hospital, Beijing Ophthalmology & Visual Sciences Key Laboratory, Beijing Tongren Eye Center, Capital Medical University, Beijing, China
| | - Jie Qin
- Beijing Tongren Hospital, Beijing Ophthalmology & Visual Sciences Key Laboratory, Beijing Tongren Eye Center, Capital Medical University, Beijing, China
| | - Xiaotong Lv
- Beijing Tongren Hospital, Beijing Ophthalmology & Visual Sciences Key Laboratory, Beijing Tongren Eye Center, Capital Medical University, Beijing, China
| | - Yushan Xu
- Beijing Tongren Hospital, Beijing Ophthalmology & Visual Sciences Key Laboratory, Beijing Tongren Eye Center, Capital Medical University, Beijing, China
| | - Dianjun Jiang
- Beijing Tongren Hospital, Beijing Ophthalmology & Visual Sciences Key Laboratory, Beijing Tongren Eye Center, Capital Medical University, Beijing, China
| | - Mingzhen Yuan
- Beijing Tongren Hospital, Beijing Ophthalmology & Visual Sciences Key Laboratory, Beijing Tongren Eye Center, Capital Medical University, Beijing, China
| | - Mingshen Sun
- Beijing Tongren Hospital, Beijing Ophthalmology & Visual Sciences Key Laboratory, Beijing Tongren Eye Center, Capital Medical University, Beijing, China
| | - Fengju Zhang
- Beijing Tongren Hospital, Beijing Ophthalmology & Visual Sciences Key Laboratory, Beijing Tongren Eye Center, Capital Medical University, Beijing, China.
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Mascolini MV, Toniolo I, Carniel EL, Fontanella CG. Ex vivo, in vivo and in silico studies of corneal biomechanics: a systematic review. Phys Eng Sci Med 2024; 47:403-441. [PMID: 38598066 PMCID: PMC11166853 DOI: 10.1007/s13246-024-01403-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2023] [Accepted: 02/08/2024] [Indexed: 04/11/2024]
Abstract
Healthy cornea guarantees the refractive power of the eye and the protection of the inner components, but injury, trauma or pathology may impair the tissue shape and/or structural organization and therefore its material properties, compromising its functionality in the ocular visual process. It turns out that biomechanical research assumes an essential role in analysing the morphology and biomechanical response of the cornea, preventing pathology occurrence, and improving/optimising treatments. In this review, ex vivo, in vivo and in silico methods for the corneal mechanical characterization are reported. Experimental techniques are distinct in testing mode (e.g., tensile, inflation tests), samples' species (human or animal), shape and condition (e.g., healthy, treated), preservation methods, setup and test protocol (e.g., preconditioning, strain rate). The meaningful results reported in the pertinent literature are discussed, analysing differences, key features and weaknesses of the methodologies adopted. In addition, numerical techniques based on the finite element method are reported, incorporating the essential steps for the development of corneal models, such as geometry, material characterization and boundary conditions, and their application in the research field to extend the experimental results by including further relevant aspects and in the clinical field for diagnostic procedure, treatment and planning surgery. This review aims to analyse the state-of-art of the bioengineering techniques developed over the years to study the corneal biomechanics, highlighting their potentiality to improve diagnosis, treatment and healing process of the corneal tissue, and, at the same, pointing out the current limits in the experimental equipment and numerical tools that are not able to fully characterize in vivo corneal tissues non-invasively and discourage the use of finite element models in daily clinical practice for surgical planning.
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Affiliation(s)
- Maria Vittoria Mascolini
- Department of Industrial Engineering, University of Padova, Padova, Italy
- Centre for Mechanics of Biological Materials, University of Padova, Padova, Italy
| | - Ilaria Toniolo
- Department of Industrial Engineering, University of Padova, Padova, Italy.
- Centre for Mechanics of Biological Materials, University of Padova, Padova, Italy.
| | - Emanuele Luigi Carniel
- Department of Industrial Engineering, University of Padova, Padova, Italy
- Centre for Mechanics of Biological Materials, University of Padova, Padova, Italy
| | - Chiara Giulia Fontanella
- Department of Industrial Engineering, University of Padova, Padova, Italy
- Centre for Mechanics of Biological Materials, University of Padova, Padova, Italy
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Gómez C, Piñero DP, Paredes M, Alió JL, Cavas F. Study of the Influence of Boundary Conditions on Corneal Deformation Based on the Finite Element Method of a Corneal Biomechanics Model. Biomimetics (Basel) 2024; 9:73. [PMID: 38392119 PMCID: PMC10886865 DOI: 10.3390/biomimetics9020073] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2023] [Revised: 01/15/2024] [Accepted: 01/18/2024] [Indexed: 02/24/2024] Open
Abstract
Implementing in silico corneal biomechanical models for surgery applications can be boosted by developing patient-specific finite element models adapted to clinical requirements and optimized to reduce computational times. This research proposes a novel corneal multizone-based finite element model with octants and circumferential zones of clinical interest for material definition. The proposed model was applied to four patient-specific physiological geometries of keratoconus-affected corneas. Free-stress geometries were calculated by two iterative methods, the displacements and prestress methods, and the influence of two boundary conditions: embedded and pivoting. The results showed that the displacements, stress and strain fields differed for the stress-free geometry but were similar and strongly depended on the boundary conditions for the estimated physiological geometry when considering both iterative methods. The comparison between the embedded and pivoting boundary conditions showed bigger differences in the posterior limbus zone, which remained closer in the central zone. The computational calculation times for the stress-free geometries were evaluated. The results revealed that the computational time was prolonged with disease severity, and the displacements method was faster in all the analyzed cases. Computational times can be reduced with multicore parallel calculation, which offers the possibility of applying patient-specific finite element models in clinical applications.
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Affiliation(s)
- Carmelo Gómez
- International School of Doctorate, Technical University of Cartagena, 30202 Cartagena, Spain
| | - David P Piñero
- Department of Optics, Pharmacology and Anatomy, University of Alicante, 03690 Alicante, Spain
| | - Manuel Paredes
- ICA, Université de Toulouse, UPS, INSA, ISAE-SUPAERO, MINES-ALBI, CNRS, 3 rue Caroline Aigle, 31400 Toulouse, France
| | - Jorge L Alió
- Cornea, Cataract and Refractive Surgery Department, VISSUM, 03016 Alicante, Spain
- Division of Ophthalmology, Department of Pathology and Surgery, Faculty of Medicine, Miguel Hernández University, 03202 Alicante, Spain
| | - Francisco Cavas
- Department of Structures, Construction and Graphic Expression, Technical University of Cartagena, 30202 Cartagena, Spain
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Wang C, Shen M, Song Y, Chang L, Yang Y, Li Y, Liu T, Wang Y. Biaxial hyperelastic and anisotropic behaviors of the corneal anterior central stroma along the preferential fibril orientations. Part I: Measurement and calibration of personalized stress-strain curves. Exp Eye Res 2023; 236:109677. [PMID: 37827443 DOI: 10.1016/j.exer.2023.109677] [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: 04/17/2023] [Revised: 09/09/2023] [Accepted: 10/09/2023] [Indexed: 10/14/2023]
Abstract
Lacking specimens is the biggest limitation of studying the mechanical behaviors of human corneal. Extracting stress-strain curves is the crucial step in investigating hyperelastic and anisotropic properties of human cornea. 15 human corneal specimens extracted from the small incision lenticule extraction (SMILE) surgery were applied in this study. To accurately measure the personalized true stress-strain curve using corneal lenticules, the digital image correlation (DIC) method and finite element method were used to calibrate the stress and the strain of the biaxial extension test. The hyperelastic load-displacement curves obtained from the biaxial extension test were performed in preferential fibril orientations, which are arranged along the nasal-temporal (NT) and the superior-inferior (SI) directions within the anterior central stroma. The displacement and strain fields were accurately calibrated and calculated using the digital image correlation (DIC) method. A conversion equation was given to convert the effective engineering strain to the true strain. The stress field distribution, which was simulated using the finite element method, was verified. Based on this, the effective nominal stress with personalized characteristics was calibrated. The personalized stress-strain curves containing individual characteristic, like diopter and anterior surface curvature, was accurately measured in this study. These results provide an experimental method using biaxial tensile test with corneal lenticules. It is the foundation for investigating the hyperelasticity and anisotropy of the central anterior stroma of human cornea.
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Affiliation(s)
- Congzheng Wang
- Department of Mechanics, School of Mechanical Engineering, Tianjin University, Tianjin, 300350, China
| | - Min Shen
- Department of Mechanics, School of Mechanical Engineering, Tianjin University, Tianjin, 300350, China.
| | - Yi Song
- Tianjin Key Laboratory of Ophthalmology and Visual Science, Tianjin Eye Hospital, Tianjin Eye Institute, Nankai University Affiliated Eye Hospital, Nankai University, Tianjin, 300020, China; Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, 300070, China
| | - Le Chang
- Tianjin Key Laboratory of Ophthalmology and Visual Science, Tianjin Eye Hospital, Tianjin Eye Institute, Nankai University Affiliated Eye Hospital, Nankai University, Tianjin, 300020, China; Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, 300070, China
| | - Yaqing Yang
- Department of Mechanics, School of Mechanical Engineering, Tianjin University, Tianjin, 300350, China
| | - Yikuan Li
- Department of Mechanics, School of Mechanical Engineering, Tianjin University, Tianjin, 300350, China
| | - Taiwei Liu
- Department of Mechanics, School of Mechanical Engineering, Tianjin University, Tianjin, 300350, China; Department of Engineering Mechanics, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, 800 Dong Chuan Road, Shanghai, 200240, China
| | - Yan Wang
- Tianjin Key Laboratory of Ophthalmology and Visual Science, Tianjin Eye Hospital, Tianjin Eye Institute, Nankai University Affiliated Eye Hospital, Nankai University, Tianjin, 300020, China; Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, 300070, China
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Cao H, Jhanji V, Wang Y. Relationship between postoperative residual refractive error and preoperative corneal stiffness in small-incision lenticule extraction. J Cataract Refract Surg 2023; 49:942-948. [PMID: 37379041 DOI: 10.1097/j.jcrs.0000000000001250] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Accepted: 06/21/2023] [Indexed: 06/29/2023]
Abstract
PURPOSE To explore the relationship between postoperative residual refractive error and preoperative corneal stiffness after small-incision lenticule extraction (SMILE). SETTING Hospital clinic. DESIGN Retrospective cohort study. METHODS Corneal stiffness was evaluated using the stress-strain index (SSI). Associations between postoperative spherical equivalent (SE) and corneal stiffness were determined using longitudinal regression analysis after adjustment for sex, age, preoperative SE, and other variables. The cohort was divided into halves to compare risk ratios for residual refraction in corneas with different SSI values. Low SSI values were defined as having less-stiff corneas and others as having stiffer corneas. RESULTS 287 patients (287 eyes) were included. Greater undercorrection was found in less-stiff corneas across all follow-up timepoints (less-stiff corneas: 1 day: -0.36 ± 0.45 diopters [D], 1 month: -0.22 ± 0.36 D, and 3 months: -0.13 ± 0.15 D; stiffer corneas: -0.22 ± 0.37 D, -0.14 ± 0.35 D, and -0.05 ± 0.11 D, respectively). Postoperative refraction exhibited a mean 0.05 D undercorrection for every 0.1-unit decrease in the SSI after adjustment for variables. The SSI accounted for nearly 10% of the variance in refractive outcomes. Less-stiff corneas increased the risk ratio of postoperative absolute SE >0 D and ≥0.25 D by 2.242 (95% CI, 1.334-3.768) and 3.023 (95% CI, 1.466-6.233), respectively, compared with stiffer corneas. CONCLUSIONS Postoperative residual refractive error was associated with preoperative corneal stiffness. Patients with less-stiff corneas had a 2- to 3-fold increased risk of residual refractive error after SMILE. Preoperative analysis of corneal stiffness can help modify nomogram algorithms of surgery and improve the predictability of refractive outcomes.
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Affiliation(s)
- Huazheng Cao
- From the School of Medicine, Nankai University, Tianjin, China (Cao); Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania (Jhanji); Tianjin Eye Hospital, Tianjin Key Lab of Ophthalmology and Visual Science, Tianjin Eye Institute, Nankai University Affiliated Eye Hospital, Tianjin, China (Wang); Nankai Eye Institute, Nankai University, Tianjin, China (Wang)
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Wang Y, Cao H, Chen W, Bao F, Elsheikh A. Editorial: How can corneal biomechanics help with clinical applications? Front Bioeng Biotechnol 2023; 11:1186938. [PMID: 37214299 PMCID: PMC10192889 DOI: 10.3389/fbioe.2023.1186938] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2023] [Accepted: 04/27/2023] [Indexed: 05/24/2023] Open
Affiliation(s)
- Yan Wang
- Tianjin Key Lab of Ophthalmology and Visual Science, Tianjin Eye Hospital, Tianjin Eye Institute, Nankai University Affiliated Eye Hospital, Tianjin, China
- Nankai University Eye Institute, Nankai University, Tianjin, China
| | - HuaZheng Cao
- Nankai University Eye Institute, Nankai University, Tianjin, China
- School of Medicine, Nankai University, Tianjin, China
| | - WeiYi Chen
- College of Biomedical Engineering, Taiyuan University of Technology, Taiyuan, China
| | - FangJun Bao
- Eye Hospital, Wenzhou Medical University, Wenzhou, China
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
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7
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Yang S, Zhang J, Tan Y, Wang Y. Unraveling the mechanobiology of cornea: From bench side to the clinic. Front Bioeng Biotechnol 2022; 10:953590. [PMID: 36263359 PMCID: PMC9573972 DOI: 10.3389/fbioe.2022.953590] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2022] [Accepted: 09/06/2022] [Indexed: 11/18/2022] Open
Abstract
The cornea is a transparent, dome-shaped structure on the front part of the eye that serves as a major optic element and a protector from the external environment. Recent evidence shows aberrant alterations of the corneal mechano-environment in development and progression of various corneal diseases. It is, thus, critical to understand how corneal cells sense and respond to mechanical signals in physiological and pathological conditions. In this review, we summarize the corneal mechano-environment and discuss the impact of these mechanical cues on cellular functions from the bench side (in a laboratory research setting). From a clinical perspective, we comprehensively review the mechanical changes of corneal tissue in several cornea-related diseases, including keratoconus, myopia, and keratectasia, following refractive surgery. The findings from the bench side and clinic underscore the involvement of mechanical cues in corneal disorders, which may open a new avenue for development of novel therapeutic strategies by targeting corneal mechanics.
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Affiliation(s)
- Shu Yang
- Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, China
- Tianjin Eye Institute, Tianjin Key Lab of Ophthalmology and Visual Science, Tianjin Eye Hospital, Tianjin, China
- Department of Ophthalmology, The First People’s Hospital of Huzhou, Huzhou, Zhejiang, China
| | - Jing Zhang
- Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, China
- Tianjin Eye Institute, Tianjin Key Lab of Ophthalmology and Visual Science, Tianjin Eye Hospital, Tianjin, China
- School of Optometry, Hong Kong Polytechnic University, Hong Kong SAR, China
| | - Youhua Tan
- Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen, China
- Department of Biomedical Engineering, Hong Kong Polytechnic University, Hong Kong SAR, China
- *Correspondence: Youhua Tan, ; Yan Wang,
| | - Yan Wang
- Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, China
- Tianjin Eye Institute, Tianjin Key Lab of Ophthalmology and Visual Science, Tianjin Eye Hospital, Tianjin, China
- *Correspondence: Youhua Tan, ; Yan Wang,
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Foster WJ, Berg BW, Luminais SN, Hadayer A, Schaal S. Computational Modeling of Ophthalmic Procedures: Computational Modeling of Ophthalmic Procedures. Am J Ophthalmol 2022; 241:87-107. [PMID: 35358485 PMCID: PMC9444883 DOI: 10.1016/j.ajo.2022.03.023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2021] [Revised: 01/16/2022] [Accepted: 03/17/2022] [Indexed: 11/01/2022]
Abstract
PURPOSE To explore how finite-element calculations can continue to contribute to diverse problems in ophthalmology and vision science, we describe our recent work on modeling the force on the peripheral retina in intravitreal injections and how that force increases with shorter, smaller gauge needles. We also present a calculation that determines the location and stress on a retinal pigment epithelial detachment during an intravitreal injection, the possibility that stress induced by the injection can lead to a tear of the retinal pigment epithelium. BACKGROUND Advanced computational models can provide a critical insight into the underlying physics in many surgical procedures, which may not be intuitive. METHODS The simulations were implemented using COMSOL Multiphysics. We compared the monkey retinal adhesive force of 18 Pa with the results of this study to quantify the maximum retinal stress that occurs during intravitreal injections. CONCLUSIONS Currently used 30-gauge needles produce stress on the retina during intravitreal injections that is only slightly below the limit that can create retinal tears. As retina specialists attempt to use smaller needles, the risk of complications may increase. In addition, we find that during an intravitreal injection, the stress on the retina in a pigment epithelial detachment occurs at the edge of the detachment (found clinically), and the stress is sufficient to tear the retina. These findings may guide physicians in future clinical research. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.
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Affiliation(s)
- William J Foster
- From the Department of Bioengineering (W.J.F.), Lewes Katz School of Medicine (B.W.B., S.N.L.), Temple University, Philadelphia, Pennsylvania, USA; Altasciences, Montréal, Québec, Canada (W.J.F.).
| | - Brian W Berg
- From the Department of Bioengineering (W.J.F.), Lewes Katz School of Medicine (B.W.B., S.N.L.), Temple University, Philadelphia, Pennsylvania, USA
| | - Steven N Luminais
- From the Department of Bioengineering (W.J.F.), Lewes Katz School of Medicine (B.W.B., S.N.L.), Temple University, Philadelphia, Pennsylvania, USA
| | - Amir Hadayer
- Department of Ophthalmology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel (A.H.)
| | - Shlomit Schaal
- Department of Ophthalmology, University of Massachusetts Medical School, Worcester, Massachusetts, USA (S.S.)
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Wang C, Li X, Guo Y, He R, Guo H, Chen W. Effects of Laser In Situ Keratomileusis and Small-Incision Lenticule Extraction on Corneal Biomechanical Behavior: A Finite Element Analysis. Front Bioeng Biotechnol 2022; 10:855367. [PMID: 35480973 PMCID: PMC9035518 DOI: 10.3389/fbioe.2022.855367] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2022] [Accepted: 02/21/2022] [Indexed: 11/13/2022] Open
Abstract
Myopia, which is the result of the uncoordinated development of the eyeball, has become a major public health focus worldwide. Laser in situ keratomileusis (LASIK) and small-incision lenticule extraction (SMILE) have been successfully used in modern corneal refractive surgery. However, there are still controversies about postoperative results of LASIK and SMILE. In this study, a three-dimensional finite element model of the cornea was constructed based on the elevation and pachymetry data of a female volunteer. Surgical parameters, magnitudes of myopic correction, and intraocular pressure (IOP) were varied. Furthermore, an iterative algorithm was applied to retrieve the free-stress state of the intact corneal model, LASIK model, and SMILE model. To better evaluate the differences between LASIK and SMILE procedures, the displacement and Von Mises stress on the anterior and posterior corneal surface along the x- and y-axes were analyzed. Results for the zero-pressure model showed larger displacement compared to the image-based corneal model, suggesting that the initial corneal pre-stress stiffens the response of the cornea, both in the intact cornea and under refractive surgery. In addition, the displacement on the corneal surface in LASIK (both zero-pressure and image-based model) was obviously higher than that of the SMILE model. In contrast, SMILE increased Von Mises stress in the corneal cap and reduced Von Mises stress in the residual stromal bed compared with the LASIK model. However, the maximum Von Mises stress in the SMILE model was still smaller than that of the LASIK model. Moreover, the displacement and Von Mises stress on the residual stromal bed increased linearly with IOP. Overall, LASIK and SMILE refractive surgery could change biomechanical behaviors of the cornea. Compared to LASIK refractive surgery, SMILE may present a lower risk of ectasia. Creating a corneal cap rather than a corneal flap may have an advantage in improving corneal biomechanical stability.
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Affiliation(s)
- Chenyan Wang
- College of Biomedical Engineering, Taiyuan University of Technology, Taiyuan, China
| | - Xiaona Li
- College of Biomedical Engineering, Taiyuan University of Technology, Taiyuan, China
- *Correspondence: Xiaona Li, ; Weiyi Chen,
| | - Yuan Guo
- College of Biomedical Engineering, Taiyuan University of Technology, Taiyuan, China
| | - Rui He
- Department of Excimer Laser, Shanxi Eye Hospital, Taiyuan, China
| | - Hongmei Guo
- College of Biomedical Engineering, Taiyuan University of Technology, Taiyuan, China
| | - Weiyi Chen
- College of Biomedical Engineering, Taiyuan University of Technology, Taiyuan, China
- *Correspondence: Xiaona Li, ; Weiyi Chen,
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10
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Zhang D, Qin X, Zhang H, Li L. Time-varying regularity of changes in biomechanical properties of the corneas after removal of anterior corneal tissue. Biomed Eng Online 2021; 20:113. [PMID: 34801040 PMCID: PMC8606087 DOI: 10.1186/s12938-021-00948-7] [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: 05/10/2021] [Accepted: 11/03/2021] [Indexed: 11/13/2022] Open
Abstract
Background The corneal biomechanical properties with the prolongation of time after corneal refractive surgery are important for providing a mechanical basis for the occurrence of clinical phenomena such as iatrogenic keratectasia and refractive regression. The aim of this study was to explore the changes of corneal elastic modulus, and stress relaxation properties from the 6-month follow-up observations of rabbits after a removal of anterior corneal tissue in simulation to corneal refractive surgery. Methods The anterior corneal tissue, 6 mm in diameter and 30–50% of the original corneal thickness, the left eye of the rabbit was removed, and the right eye was kept as the control. The rabbits were normally raised and nursed for 6 months, during which corneal morphology data, and both of corneal hysteresis (CH) and corneal resistance factor (CRF) were gathered. Uniaxial tensile tests of corneal strips were performed at months 1, 3, and 6 from 7 animals, and corneal collagen fibrils were observed at months 1, 3, and 6 from 1 rabbit, respectively. Results Compared with the control group, there were statistical differences in the curvature radius at week 2 and month 3, and both CH and CRF at months 1, 2, and 6 in experiment group; there were statistical differences in elastic modulus at 1, 3, and month 6, and stress relaxation degree at month 3 in experiment group. The differences in corneal elastic modulus, stress relaxation degree and the total number of collagen fibrils between experiment and control groups varied gradually with time, and showed significant changes at the 3rd month after the treatment. Conclusions Corneas after a removal of anterior corneal tissue undergo dynamic changes in corneal morphology and biomechanical properties. The first 3 months after treatment could be a critical period. The variation of corneal biomechanical properties is worth considering in predicting corneal deformation after a removal of anterior corneal tissue.
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Affiliation(s)
- Di Zhang
- School of Biomedical Engineering, Capital Medical University, Beijing, 100069, China.,Beijing Key Laboratory of Fundamental Research on Biomechanics in Clinical Application, Capital Medical University, Beijing, 100069, China
| | - Xiao Qin
- School of Biomedical Engineering, Capital Medical University, Beijing, 100069, China.,Beijing Key Laboratory of Fundamental Research on Biomechanics in Clinical Application, Capital Medical University, Beijing, 100069, China
| | - Haixia Zhang
- School of Biomedical Engineering, Capital Medical University, Beijing, 100069, China. .,Beijing Key Laboratory of Fundamental Research on Biomechanics in Clinical Application, Capital Medical University, Beijing, 100069, China.
| | - Lin Li
- School of Biomedical Engineering, Capital Medical University, Beijing, 100069, China. .,Beijing Key Laboratory of Fundamental Research on Biomechanics in Clinical Application, Capital Medical University, Beijing, 100069, China.
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11
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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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Update and Review of Diagnosis and Management of Post-Refractive Surgery Ectasia. J Cataract Refract Surg 2021; 48:487-499. [PMID: 34486581 DOI: 10.1097/j.jcrs.0000000000000808] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Accepted: 08/18/2021] [Indexed: 11/25/2022]
Abstract
ABSTRACT Post-Refractive Surgery Ectasia is a serious, sight-threatening, and highly - avoided complication seen after the following procedures: Laser in situ Keratomileusis, Photorefractive Keratectomy, Small Incision Lenticule Extraction, Radial and/or Arcuate Keratotomy. Specific risk factors may include age, corneal thickness, degree of refractive error, corneal topographic changes including irregular astigmatism, percent tissue ablation, and residual stromal bed. Biomarkers may be a new option to help indicate who is at greatest risk for ectasia. Visual aids including glasses or contacts lenses are often required to achieve optimal vision. Collagen crosslinking is the only treatment thought to stop progression of ectasia and prevent keratoplasty. Other surgical options may include topography-guided phototherapeutic keratectomy and intrastromal corneal ring segments. Ultimately an "ounce of prevention is a pound of cure" so careful preoperative screening and ultimately offering the safest and most effective treatments for patients is arguably the most important job of the refractive surgeon.
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