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Kharmyssov C, Utegulov Z. Brillouin Biosensing of Viscoelasticity across Phase Transitions in Ovine Cornea. BIOSENSORS 2024; 14:371. [PMID: 39194600 DOI: 10.3390/bios14080371] [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: 05/25/2024] [Revised: 07/25/2024] [Accepted: 07/28/2024] [Indexed: 08/29/2024]
Abstract
Noninvasive in situ monitoring of viscoelastic characteristics of corneal tissue at elevated temperatures is pivotal for mechanical property-informed refractive surgery techniques, including thermokeratoplasty and photorefractive keratectomy, requiring precise thermal modifications of the corneal structure during these surgical procedures. This study harnesses Brillouin light scattering spectroscopy as a biosensing platform to noninvasively probe the viscoelastic properties of ovine corneas across a temperature range of 25-64 °C. By submerging the tissue samples in silicone oil, consistent hydration and immiscibility are maintained, allowing for their accurate sensing of temperature-dependent mechanical behaviors. We identify significant phase transitions in the corneal tissue, particularly beyond 40 °C, likely due to collagen unfolding, marking the beginning of thermal destabilization. A subsequent transition, observed beyond 60 °C, correlates with collagen denaturation. These phase transformations highlight the cornea's sensitivity to both physiologically reversible and irreversible viscoelastic changes induced by mild to high temperatures. Our findings underscore the potential of the Brillouin biosensing technique for real-time diagnostics of corneal biomechanics during refractive surgeries to attain optimized therapeutic outcomes.
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Affiliation(s)
| | - Zhandos Utegulov
- Department of Physics, School of Sciences and Humanities, Nazarbayev University, Astana 010000, Kazakhstan
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2
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Frigelli M, Büchler P, Kling S. Dynamic evaluation of corneal cross-linking and osmotic diffusion effects using optical coherence elastography. Sci Rep 2024; 14:16614. [PMID: 39025900 PMCID: PMC11258322 DOI: 10.1038/s41598-024-67278-1] [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: 02/13/2024] [Accepted: 07/09/2024] [Indexed: 07/20/2024] Open
Abstract
Dynamic deformation events induced by osmosis or photochemical stiffening substantially influence geometrical and mechanical assessments in post-mortem corneas, therefore need to be carefully monitored in experimental settings. In this study, we employed optical coherence elastography (OCE) to quantify dynamic deformation processes at high resolution in freshly enucleated porcine corneas. Osmotic effects were studied by immerging n = 9 eyes in preservation media of three different tonicities. Dynamic processes underlying corneal cross-linking (CXL) were studied by subjecting n = 6 eyes to standard Dresden treatment, while three control groups were used. The entire procedures were performed under an OCE setup during up to 80 min, acquiring a volumetric scan every 20 s. Changes in OCE-derived axial deformations were incrementally calculated between consecutive scans. Preservation conditions had a strong influence on the observed strain patterns, which were consistent with the tonicity of the medium (swelling in hypotonic, deswelling in hypertonic environment). In the CXL group, we observed deswelling of the anterior stroma 10 min after starting the UV irradiation, which was not observed in any control group (p = 0.007). The presented results proved OCE to be a valuable technique to quantify subtle dynamic biomechanical alterations in the cornea resulting from CXL and preservation solutions.
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Affiliation(s)
- Matteo Frigelli
- ARTORG Center for Biomedical Engineering Research, University of Bern, Bern, Switzerland
| | - Philippe Büchler
- ARTORG Center for Biomedical Engineering Research, University of Bern, Bern, Switzerland
| | - Sabine Kling
- ARTORG Center for Biomedical Engineering Research, University of Bern, Bern, Switzerland.
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Francis M, Sinha Roy A. Re: Randleman et al.: Subclinical keratoconus detection and characterization using motion-tracking Brillouin microscopy (Ophthalmology. 2024;131:310-321). Ophthalmology 2024; 131:e22-e23. [PMID: 38219145 DOI: 10.1016/j.ophtha.2023.12.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2023] [Revised: 11/09/2023] [Accepted: 12/07/2023] [Indexed: 01/15/2024] Open
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Zhang S, Zhang W, Xiao S, Zhang Y, Chen D, Liu X, Wu Y. Efficacy of enzyme‑induced collagen crosslinking on porcine cornea. Exp Ther Med 2024; 27:87. [PMID: 38274339 PMCID: PMC10809311 DOI: 10.3892/etm.2024.12377] [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: 02/20/2023] [Accepted: 11/22/2023] [Indexed: 01/27/2024] Open
Abstract
The purpose of the present study was to investigate the effect of a new crosslinking (CXL) method, induced by enzymes, on porcine corneas. Corneal strip (10x3 mm) pairs obtained from 60 fresh porcine eyes were harvested and divided into four groups, Groups A-D. Each pair of corneal strips was incised from the central part of the same cornea; one was incubated in transglutaminase (Tgase) solution (microbial Tgase 2 produced by tissue engineering) and the other remained untreated as a control. CXL strips of Groups A-D were incubated with 2, 1, 0.5 and 0.25 U/ml Tgase solution, respectively at 37˚C for 30 min. After that, tensile strain measurements were performed for all strips. One cornea from each group was chosen randomly for hematoxylin and eosin, and Masson staining to identify histological morphology changes. The elastic modulus of treated corneas of Groups A-D were 6.56±2.93, 4.72±1.29, 5.24±2.13 and 3.48±1.60 MPa (mean ± SD), respectively at a strain of 20%, and had a 66, 43, 36 and -6% increase compared with those of their control strips. Compared with the control strips, the elastic modulus of the treated strips significantly increased in Groups A-C. The central corneal thickness of the treated corneas in Groups A-D were 1.54±0.14, 1.41±0.15, 1.47±0.11 and 1.43±0.13 µm, respectively; however, there was not a statistically significant difference compared with the control group. No reduction in corneal transparency was observed, and no obvious abnormalities were found in corneal morphology. CXL mediated by enzymes can lead to a notable enhancement in the biomechanical characteristics of the cornea while maintaining its structural integrity. Enzyme-induced CXL could be a new generation CXL method for strengthening the cornea.
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Affiliation(s)
- Shijie Zhang
- Department of Ophthalmology, Peking University First Hospital, Peking University, Beijing 100034, P.R. China
| | - Wenbo Zhang
- Department of Ophthalmology, Peking University First Hospital, Peking University, Beijing 100034, P.R. China
| | - Shiyu Xiao
- Department of Ophthalmology, Peking University First Hospital, Peking University, Beijing 100034, P.R. China
| | - Yanzhen Zhang
- Department of Ophthalmology, Peking University First Hospital, Peking University, Beijing 100034, P.R. China
| | - Duo Chen
- Key Laboratory for Biomechanics and Mechanobiology of Ministry of Education, School of Biological Sciences and Medical Engineering, Beihang University, Beijing 100191, P.R. China
- Beijing Advanced Innovation Centre for Biomedical Engineering, Beihang University, Beijing 100083, P.R. China
| | - Xiaoyu Liu
- Key Laboratory for Biomechanics and Mechanobiology of Ministry of Education, School of Biological Sciences and Medical Engineering, Beihang University, Beijing 100191, P.R. China
- Beijing Advanced Innovation Centre for Biomedical Engineering, Beihang University, Beijing 100083, P.R. China
| | - Yuan Wu
- Department of Ophthalmology, Peking University First Hospital, Peking University, Beijing 100034, P.R. China
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Borrego-Sanz L, Morales-Fernández L, Saénz-Francés San Baldomero F, Díaz Valle D, Pato Cour E, Méndez Fernández R, García Feijóo J, Rodríguez Rodríguez L. Corneal Biomechanics in Non-infectious Uveitis Measured by Corvis ST: A Pilot Study. Ocul Immunol Inflamm 2023; 31:1765-1771. [PMID: 35980346 DOI: 10.1080/09273948.2022.2108462] [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: 12/29/2021] [Accepted: 07/26/2022] [Indexed: 10/15/2022]
Abstract
PURPOSE To assess differences between corneal biomechanical properties in patients with non-infectious uveitis and healthy subjects using CorVis. METHODS 77 patients with non-infectious uveitis and 47 control subjects were recruited. Biomechanical parameters were measured: deformation amplitude (DA), A-1 length and A-2 length (L1, L2), A-1 velocity and A-2 velocity (V1, V2), peak distance (PD) and HC radius (highest concavity radius). AUC ROC and correlation between clinical variables and biomechanical properties were determined. RESULTS Lower HC Radius and IOPb and higher DA and V1 was found in uveitis group. Statistical differences between cases using systemic medications and those with topical treatment were found in L1. Differences were showed between those cases with active and inactive uveitis in PD, DA, V2 and L2. The biomechanical parameter with the best discriminatory capacity of uveitis disease was HC Radius. CONCLUSION Differences in corneal biomechanical properties between non-infectious uveitis and healthy eyes were found.
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Affiliation(s)
- Lara Borrego-Sanz
- Ophthalmology Department, Clínico San Carlos Hospital, Madrid, Spain
| | | | | | - David Díaz Valle
- Ophthalmology Department, Clínico San Carlos Hospital, Madrid, Spain
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Zhang H, Asroui L, Tarib I, Dupps WJ, Scarcelli G, Randleman JB. Motion-Tracking Brillouin Microscopy Evaluation of Normal, Keratoconic, and Post-Laser Vision Correction Corneas. Am J Ophthalmol 2023; 254:128-140. [PMID: 36963605 PMCID: PMC11108093 DOI: 10.1016/j.ajo.2023.03.018] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2022] [Revised: 03/06/2023] [Accepted: 03/11/2023] [Indexed: 03/26/2023]
Abstract
PURPOSE To characterize focal biomechanical differences between normal, keratoconic, and post-laser vision correction (LVC) corneas using motion-tracking Brillouin microscopy. DESIGN Prospective cross-sectional study. METHODS Thirty eyes from 30 patients (10 normal controls [Controls], 10 post-LVC, and 10 stage I or II keratoconus [KC]) had Scheimpflug and motion-tracking Brillouin microscopy imaging using a custom-built device. Mean, maximum (max) and minimum (min) Brillouin shift, spatial standard deviation, and max-min values were compared. Min values were correlated with local Brillouin values at multiple Scheimpflug imaging locations. RESULTS Mean (P < .0003), min (P < .00001), spatial standard deviation (P < .01), and max-min (P < .001) were significantly different between the groups. In post hoc pairwise comparisons, the best differentiators for group comparisons were mean (P = .0004) and min (P = .000002) for Controls vs KC, min (P = .0022) and max-min (P = .002) for Controls vs LVC, and mean (P = .0037) and min (P = .0043) for LVC vs KC. Min (area under the receiver operating characteristic = 1.0) and mean (area under the receiver operating characteristic = 0.96) performed well in differentiating Control and KC eyes. Min values correlated best with Brillouin shift values at the thinnest corneal point (r2 = 0.871, P = .001) and maximum keratometry value identified in the tangential curvature map (r2 = 0.840, P = .002). CONCLUSIONS Motion-tracking Brillouin microscopy effectively characterized focal corneal biomechanical alterations in LVC and KC and clearly differentiated these groups from Controls. Primary motion-tracking Brillouin metrics performed well in differentiating groups as compared with basic Scheimpflug metrics, in contrast to previous Brillouin studies, and identified focal changes after LVC where prior Brillouin studies did not.
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Affiliation(s)
- Hongyuan Zhang
- From The Cole Eye Institute, Cleveland Clinic (H.Z., L.A., I.T., W.J.D., J.B.R.)
| | - Lara Asroui
- From The Cole Eye Institute, Cleveland Clinic (H.Z., L.A., I.T., W.J.D., J.B.R.)
| | - Imane Tarib
- From The Cole Eye Institute, Cleveland Clinic (H.Z., L.A., I.T., W.J.D., J.B.R.)
| | - William J Dupps
- From The Cole Eye Institute, Cleveland Clinic (H.Z., L.A., I.T., W.J.D., J.B.R.); Cleveland Clinic Lerner College of Medicine of Case Western Reserve University (W.J.D., J.B.R.); Department of Biomedical Engineering, Case Western Reserve University (W.J.D.), Cleveland, Ohio
| | - Giuliano Scarcelli
- Fischell Department of Bioengineering, University of Maryland, College Park, Maryland (GS), USA
| | - J Bradley Randleman
- From The Cole Eye Institute, Cleveland Clinic (H.Z., L.A., I.T., W.J.D., J.B.R.); Cleveland Clinic Lerner College of Medicine of Case Western Reserve University (W.J.D., J.B.R.).
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Lopes BT, Elsheikh A. In Vivo Corneal Stiffness Mapping by the Stress-Strain Index Maps and Brillouin Microscopy. Curr Eye Res 2023; 48:114-120. [PMID: 35634717 DOI: 10.1080/02713683.2022.2081979] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The study of corneal stiffness in vivo has numerous clinical applications such as the measurement of intraocular pressure, the preoperative screening for iatrogenic ectasia after laser vision correction surgery and the diagnosis and treatment of corneal ectatic diseases such as keratoconus. The localised aspect of the microstructure deterioration in keratoconus leading to local biomechanical softening, corneal bulging, irregular astigmatism and ultimately loss of vision boosted the need to map the corneal stiffness to identify the regional biomechanical failure. Currently, two methods to map the corneal stiffness in vivo are integrated into devices that are either already commercially available or about to be commercialised: the stress-strain index (SSI) maps and the Brillouin Microscopy (BM). The former method produces 2D map of stiffness across the corneal surface, developed through numerical simulations using the corneal shape, its microstructure content, and the deformation behaviour under air-puff excitation. It estimates the whole stress-strain behaviour, making it possible to obtain the material tangent modulus under different intraocular pressure levels. On the other hand, BM produces a 3D map of the corneal longitudinal modulus across the corneal surface and thickness. It uses a low-power near-infrared laser beam and through a spectral analysis of the returned signal, it assesses the mechanical compressibility of the tissue as measured by the longitudinal modulus. In this paper, these two techniques are reviewed, and their advantages and limitations discussed.
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Affiliation(s)
- Bernardo T Lopes
- School of Engineering, University of Liverpool, Liverpool, UK.,Department of Ophthalmology, Federal University of São Paulo, São Paulo, Brazil
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool, UK.,Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing, China.,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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Acoustic Micro-Tapping Optical Coherence Elastography to Quantify Corneal Collagen Cross-Linking: An Ex Vivo Human Study. OPHTHALMOLOGY SCIENCE 2022; 3:100257. [PMID: 36685713 PMCID: PMC9852959 DOI: 10.1016/j.xops.2022.100257] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Revised: 10/25/2022] [Accepted: 11/08/2022] [Indexed: 11/15/2022]
Abstract
Purpose To evaluate changes in the anisotropic elastic properties of ex vivo human cornea treated with ultraviolet cross-linking (CXL) using noncontact acoustic micro-tapping optical coherence elastography (AμT-OCE). Design Acoustic micro-tapping OCE was performed on normal and CXL human donor cornea in an ex vivo laboratory study. Subjects Normal human donor cornea (n = 22) divided into 4 subgroups. All samples were stored in optisol. Methods Elastic properties (in-plane Young's, E, and out-of-plane, G, shear modulus) of normal and ultraviolet CXL-treated human corneas were quantified using noncontact AμT-OCE. A nearly incompressible transverse isotropic model was used to reconstruct moduli from AμT-OCE data. Independently, cornea elastic moduli were also measured with destructive mechanical tests (tensile extensometry and shear rheometry). Main Outcome Measures Corneal elastic moduli (in-plane Young's modulus, E, in-plane, μ, and out-of-plane, G, shear moduli) can be evaluated in both normal and CXL treated tissues, as well as monitored during the CXL procedure using noncontact AμT-OCE. Results Cross-linking induced a significant increase in both in-plane and out-of-plane elastic moduli in human cornea. The statistical mean in the paired study (presurgery and postsurgery, n = 7) of the in-plane Young's modulus, E = 3 μ , increased from 19 MPa to 43 MPa, while the out-of-plane shear modulus, G, increased from 188 kPa to 673 kPa. Mechanical tests in a separate subgroup support CXL-induced cornea moduli changes and generally agree with noncontact AμT-OCE measurements. Conclusions The human cornea is a highly anisotropic material where in-plane mechanical properties are very different from those out-of-plane. Noncontact AμT-OCE can measure changes in the anisotropic elastic properties in human cornea as a result of ultraviolet CXL.
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Vera J, Redondo B, Molina R, Jiménez R. Effects of water drinking on corneal biomechanics: The association with intraocular pressure changes. Indian J Ophthalmol 2022; 70:1222-1228. [PMID: 35326020 PMCID: PMC9240569 DOI: 10.4103/ijo.ijo_1845_21] [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] [Indexed: 11/23/2022] Open
Abstract
Purpose: We aimed to assess the impact of drinking water (500 and 1000 mL) on corneal biomechanics and determine the level of association between changes in intraocular pressure and variations in the different biomechanical properties of the cornea. Methods: A total of 39 healthy young adults ingested either 1000 mL (n = 21) or 500 mL (n = 18) of tap water in 5 min. The CorVis ST system was used to assess corneal biomechanics at baseline and at 15, 30, and 45 min after water ingestion. Results: Water drinking induced statistically significant changes in the deformation amplitude (P < 0.001, η² = 0.166), highest concavity time (P = 0.012, η² = 0.093), peak distance (P < 0.001, η² = 0.171), time and velocity of the first applanation (P < 0.001, η² = 0.288 and P = 0.016, η² = 0.087, respectively), and time and velocity of the second applanation (P = 0.030, η² = 0.074 and P = 0.001, η² = 0.132, respectively), being independent of the amount of water ingested (P > 0.05 in all cases). There were significant associations between changes in intraocular pressure and some parameters of corneal biomechanics Conclusion: Small variations in whole-body hydration status alter different biomechanical properties of the cornea, with these changes being associated with intraocular pressure levels. These findings indicate that whole-body hydration status can be considered for the diagnosis and management of different ocular conditions.
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Affiliation(s)
- Jesús Vera
- Department of Optics, Faculty of Sciences, University of Granada, Spain
| | - Beatríz Redondo
- Department of Optics, Faculty of Sciences, University of Granada, Spain
| | - Rubén Molina
- Department of Optics, Faculty of Sciences, University of Granada, Spain
| | - Raimundo Jiménez
- Department of Optics, Faculty of Sciences, University of Granada, Spain
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Intraocular pressure measurement: A Review. Surv Ophthalmol 2022; 67:1319-1331. [DOI: 10.1016/j.survophthal.2022.03.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Revised: 02/16/2022] [Accepted: 03/01/2022] [Indexed: 11/21/2022]
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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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Zhao L, Lin H, Hu Y, Chen X, Chen S, Zhang X. Corneal Lamb wave imaging for quantitative assessment of collagen cross-linking treatment based on comb-push ultrasound shear elastography. ULTRASONICS 2021; 116:106478. [PMID: 34174743 DOI: 10.1016/j.ultras.2021.106478] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Revised: 05/03/2021] [Accepted: 05/24/2021] [Indexed: 06/13/2023]
Abstract
Keratoconus, a serious corneal disorder, often causes highly irregular astigmatism and different degrees of visual impairment. Riboflavin/UVA corneal collagen cross-linking(CXL) is currently approved for effective treatment of keratoconus by enhancing the mechanical strength of collagen fibers in the cornea. However, few methods are capable of quantitatively and non-destructively assessing the mechanical properties of the cornea before and after CXL treatments. This study developed a corneal viscoelasticity imaging method based on comb-push ultrasound shear elastography (CUSE) and implemented this method on a Verasonics™ Vantage 256 ultrasound open system with a high-frequency linear array ultrasound transducer. Push beams were generated by three teeth each consisting of 10 elements (working frequency = 10.41 MHz) for inducing Lamb wave propagation in the cornea, and then the system immediately switched to the plane wave imaging mode using 60 elements in the middle (working frequency = 18 MHz). This method can provide a high-resolution 2D Lamb wave velocity image overlapping with a B-mode image as well as quantitative viscoelasticity estimation according to experimentally obtained phase velocity dispersion of Lamb waves. The validation experiments were performed on ex vivo porcine corneas, and the accuracy of elasticity estimation was verified by a tensile test. The results showed that the shear elasticity increased and the viscosity decreased after CXL treatment. The shear elasticity results (reported as mean ± standard deviation) of one control group with no CXL treatment and three CXL-treated groups named as 10 min, 30 min, and 60 min groups according to UV irradiation time were 14.62 ± 3.38 kPa, 49.47 ± 3.63 kPa, 116.54 ± 23.99 kPa, and 197.89 ± 39.64 kPa, respectively, which was in agreement with the results of tensile tests. The ultrasound safety measurement indicated that this method could have acceptable safety, but further to ocular tissue and vision function. The study demonstrated the possibility of using a commercial ultrasound system to obtain high-resolution images of corneal mechanical properties as well as the ability to quantify changes induced by CXL treatment. Therefore, the proposed method could serve as a helpful tool in the studies related in corneal biomechanics.
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Affiliation(s)
- Linfeng Zhao
- School of Biomedical Engineering, Health Science Center, Shenzhen University, Shenzhen, China; National-Regional Key Technology Engineering Laboratory for Medical Ultrasound, Shenzhen, China; Guangdong Key Laboratory for Biomedical Measurements and Ultrasound Imaging, Shenzhen, China
| | - Haoming Lin
- School of Biomedical Engineering, Health Science Center, Shenzhen University, Shenzhen, China; National-Regional Key Technology Engineering Laboratory for Medical Ultrasound, Shenzhen, China; Guangdong Key Laboratory for Biomedical Measurements and Ultrasound Imaging, Shenzhen, China
| | - Yaxin Hu
- School of Biomedical Engineering, Health Science Center, Shenzhen University, Shenzhen, China; National-Regional Key Technology Engineering Laboratory for Medical Ultrasound, Shenzhen, China; Guangdong Key Laboratory for Biomedical Measurements and Ultrasound Imaging, Shenzhen, China
| | - Xin Chen
- School of Biomedical Engineering, Health Science Center, Shenzhen University, Shenzhen, China; National-Regional Key Technology Engineering Laboratory for Medical Ultrasound, Shenzhen, China; Guangdong Key Laboratory for Biomedical Measurements and Ultrasound Imaging, Shenzhen, China
| | - Siping Chen
- School of Biomedical Engineering, Health Science Center, Shenzhen University, Shenzhen, China; National-Regional Key Technology Engineering Laboratory for Medical Ultrasound, Shenzhen, China; Guangdong Key Laboratory for Biomedical Measurements and Ultrasound Imaging, Shenzhen, China
| | - Xinyu Zhang
- School of Biomedical Engineering, Health Science Center, Shenzhen University, Shenzhen, China; National-Regional Key Technology Engineering Laboratory for Medical Ultrasound, Shenzhen, China; Guangdong Key Laboratory for Biomedical Measurements and Ultrasound Imaging, Shenzhen, China.
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Contribution of Bowman layer to corneal biomechanics. J Cataract Refract Surg 2021; 47:927-932. [PMID: 33315734 DOI: 10.1097/j.jcrs.0000000000000543] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Accepted: 11/23/2020] [Indexed: 11/26/2022]
Abstract
PURPOSE To compare the elastic modulus of thin corneal lamellas using 2D stress-strain extensometry in healthy ex vivo human corneal lamellas with or without the presence of Bowman layer. SETTING Center for Applied Biotechnology and Molecular Medicine, University of Zurich, Switzerland; ELZA Institute, Dietikon, Switzerland; Department of Ophthalmology, Philipps University of Marburg, Germany. DESIGN Prospective experimental laboratory study. METHODS Healthy human corneas were stripped of Descemet membrane and the endothelium for Descemet membrane endothelial keratoplasty. After epithelium removal, corneas were divided into 2 groups. In Group 1, Bowman layer was ablated with an excimer laser (20 μm thick, 10 mm). In Group 2, Bowman layer was left intact. Then, a lamella was cut from the anterior cornea with an automated microkeratome. Elastic and viscoelastic material properties were analyzed by 2D stress-strain extensometry between 0.03 and 0.70 N. RESULTS Twenty-six human corneas were analyzed. The mean lamella thickness was 160 ± 37 μm in corneas with Bowman layer and 155 ± 22 μm in corneas without. No statistically significant differences between flaps with and without Bowman layer were observed in the tangential elastic modulus between 5% and 20% strain (11.5 ± 2.9 kPa vs 10.8 ± 3.7 kPa, P > .278). CONCLUSIONS The presence or absence of Bowman layer did not reveal a measurable difference in corneal stiffness. This may indicate that the removal of Bowman layer during photorefractive keratectomy does not represent a disadvantage to corneal biomechanics.
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Chen A, Virk A, Harris Z, Abazari A, Honkanen R, Arbab MH. Non-contact terahertz spectroscopic measurement of the intraocular pressure through corneal hydration mapping. BIOMEDICAL OPTICS EXPRESS 2021; 12:3438-3449. [PMID: 34221670 PMCID: PMC8221940 DOI: 10.1364/boe.423741] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Revised: 05/03/2021] [Accepted: 05/04/2021] [Indexed: 05/03/2023]
Abstract
Elevated intraocular pressure (IOP) results in endothelial layer damage that can induce corneal hydration perturbations. We investigated the potential of terahertz spectroscopy in measuring the IOP levels through mapping corneal water content. We controlled the IOP levels in ex vivo rabbit and porcine eye samples while monitoring the change in corneal hydration using a terahertz time-domain spectroscopy (THz-TDS) scanner. Our results showed a statistically significant increase in the THz reflectivity between 0.4 and 0.6 THz corresponding to the increase in the IOP. Endothelial layer damage was confirmed using scanning electron microscopy (SEM) of the corneal biopsy samples. Our empirical results indicate that the THz-TDS can be used to track IOP levels through the changes in corneal hydration.
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Affiliation(s)
- Andrew Chen
- Department of Biomedical Engineering, Stony Brook University, 100 Nicolls Rd, Stony Brook, NY 11794, USA
| | - Arjun Virk
- Department of Biomedical Engineering, Stony Brook University, 100 Nicolls Rd, Stony Brook, NY 11794, USA
| | - Zachery Harris
- Department of Biomedical Engineering, Stony Brook University, 100 Nicolls Rd, Stony Brook, NY 11794, USA
| | - Azin Abazari
- Department of Ophthalmology, Renaissance School of Medicine, 101 Nicolls Rd, Stony Brook, NY 11794, USA
| | - Robert Honkanen
- Department of Ophthalmology, Renaissance School of Medicine, 101 Nicolls Rd, Stony Brook, NY 11794, USA
| | - M. Hassan Arbab
- Department of Biomedical Engineering, Stony Brook University, 100 Nicolls Rd, Stony Brook, NY 11794, USA
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Chong J, Dupps WJ. Corneal biomechanics: Measurement and structural correlations. Exp Eye Res 2021; 205:108508. [PMID: 33609511 DOI: 10.1016/j.exer.2021.108508] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Revised: 02/09/2021] [Accepted: 02/12/2021] [Indexed: 02/02/2023]
Abstract
The characterization of corneal biomechanical properties has important implications for the management of ocular disease and prediction of surgical responses. Corneal refractive surgery outcomes, progression or stabilization of ectatic disease, and intraocular pressure determination are just examples of the many key clinical problems that depend highly upon corneal biomechanical characteristics. However, to date there is no gold standard measurement technique. Since the advent of a 1-dimensional (1D) air-puff based technique for measuring the corneal surface response in 2005, advances in clinical imaging technology have yielded increasingly sophisticated approaches to characterizing the biomechanical properties of the cornea. Novel analyses of 1D responses are expanding the clinical utility of commercially-available air-puff-based instruments, and other imaging modalities-including optical coherence elastography (OCE), Brillouin microscopy and phase-decorrelation ocular coherence tomography (PhD-OCT)-offer new opportunities for probing local biomechanical behavior in 3-dimensional space and drawing new inferences about the relationships between corneal structure, mechanical behavior, and corneal refractive function. These advances are likely to drive greater clinical adoption of in vivo biomechanical analysis and to support more personalized medical and surgical decision-making.
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Affiliation(s)
- Jillian Chong
- Cleveland Clinic Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA
| | - William J Dupps
- Cleveland Clinic Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA; Dept. of Ophthalmology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve Univ, Cleveland, OH, USA; Dept. of Biomedical Engineering, Lerner Research Institute and Case Western Reserve Univ, Cleveland, OH, USA.
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16
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Effects of caffeine intake on the biomechanical properties of the cornea: a placebo-controlled, double-blind, crossover pilot study in low caffeine consumers. Graefes Arch Clin Exp Ophthalmol 2020; 258:2449-2458. [DOI: 10.1007/s00417-020-04835-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2020] [Revised: 07/01/2020] [Accepted: 07/07/2020] [Indexed: 10/23/2022] Open
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17
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Clayson K, Sandwisch T, Ma Y, Pavlatos E, Pan X, Liu J. Corneal Hydration Control during Ex Vivo Experimentation Using Poloxamers. Curr Eye Res 2019; 45:111-117. [PMID: 31474157 DOI: 10.1080/02713683.2019.1663387] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Purpose: The purpose of this study was to develop an effective treatment method using poloxamers to restore and maintain physiological hydration in postmortem porcine and human corneas during ex vivo experimentation, and to compare corneal inflation response with or without treatment.Materials and Methods: Corneal buttons obtained from whole globes (n = 30 porcine, n = 8 human) were treated with various concentrations of poloxamer 188 (P188, a synthetic macromolecule surfactant) for 24 hrs to identify the concentration that would return the cornea to near-physiological hydration (i.e. H = 3.2). Whole globes (n = 12 porcine, n = 16 human) were also used to monitor central corneal thickness (CCT) during deswelling treatment. Inflation testing from 5 to 30 mmHg was performed in the porcine globes and a subset of human globes to characterize the mechanical response of the cornea after treatment.Results: Physiological hydration was obtained after 24 hrs immersion in 3.25% P188 for porcine corneas and 4.25% P188 treatment for human corneas. CCT was stabilized and returned to physiological levels after 24 hrs of treatment in 3.25% P188 in porcine (891 ± 66 µm) and 4.25% P188 in human (574 ± 34 µm) whole globes. Corneal axial strains at 30 mmHg were significantly larger at physiological hydration than in swollen cornea in both porcine (-6.42%±1.50% vs. -3.64%±1.05%, p = .004) and human (-2.85%±0.09% in vs. -1.53%±0.27%, p = .031) eyes.Conclusions: Our results suggest that P188 treatment was effective in restoring and maintaining near physiological corneal hydration during ex vivo testing, and hydration appeared to significantly impact corneal inflation response in both porcine and human eyes.
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Affiliation(s)
- Keyton Clayson
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, USA.,Biophysics Graduate Program, The Ohio State University, Columbus, Ohio, USA
| | - Thomas Sandwisch
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, USA
| | - Yanhui Ma
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, USA
| | - Elias Pavlatos
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, USA
| | - Xueliang Pan
- Department of Biomedical Informatics, The Ohio State University, Columbus, Ohio, USA
| | - Jun Liu
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, USA.,Biophysics Graduate Program, The Ohio State University, Columbus, Ohio, USA.,Department of Ophthalmology and Visual Science, The Ohio State University, Columbus, Ohio, USA
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Seiler TG, Shao P, Eltony A, Seiler T, Yun SH. Brillouin Spectroscopy of Normal and Keratoconus Corneas. Am J Ophthalmol 2019; 202:118-125. [PMID: 30772345 DOI: 10.1016/j.ajo.2019.02.010] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Revised: 01/28/2019] [Accepted: 02/05/2019] [Indexed: 11/17/2022]
Abstract
PURPOSE To investigate the age dependence of Brillouin spectroscopy of the cornea and to compare normal and keratoconus corneas. DESIGN Retrospective case-control study. METHODS Study Population: Healthy patients and patients suffering from keratoconus seen at the Institut für Refraktive und Ophthalmo-Chirurgie (IROC) between December 2016 and March 2017. Brillouin frequency shifts of patients of 2 different groups were examined with Brillouin spectroscopy perpendicular to the corneal surface. Group 1 consisted of 47 healthy eyes, whereas Group 2 included 36 eyes with keratoconus of unclear progression. Besides Brillouin examinations, corneal tomographies were acquired so that correlations and comparisons between geometric parameters and Brillouin frequency shifts could be evaluated. MAIN OUTCOME MEASURES Corneal Brillouin frequency shifts averaged over full corneal thickness. RESULTS A significant correlation between age and central Brillouin frequency shift was identified (P = .011) with an increase in Brillouin frequency shift of 4 MHz per decade in normal corneas. Keratoconus corneas have a significantly reduced Brillouin frequency shift at the thinnest point compared to normal corneas (5.7072 ± 0.0214 vs 5.7236 ± 0.0146 GHz, P < .001). The Brillouin frequency shift at the point of maximum posterior elevation showed best correlation with geometry-derived keratoconus indices. The receiver operating characteristic curve analysis of Brillouin frequency shift showed substantially worse sensitivity and specificity compared to Kmax and thinnest pachymetry for keratoconus detection. CONCLUSION Noninvasive Brillouin spectroscopy adds clinical information about the biomechanical state of the cornea perpendicular to the surface. An age-dependent stiffening of the cornea has been found and keratoconus corneas are statistically significantly different from normal corneas, but for precise differentiating of keratoconus stages (including normal corneas) the method is currently neither specific nor sensitive enough. Further development including standardized mapping and establishment of new indices may increase the potential of Brillouin spectroscopy substantially.
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Affiliation(s)
- Theo G Seiler
- Institut für Refraktive und Ophthalmo-Chirurgie (IROC), Zürich, Switzerland; Wellman Center for Photomedicine - Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA; Universitätsklinik für Augenheilkunde, Inselspital, Bern, Switzerland.
| | - Peng Shao
- Wellman Center for Photomedicine - Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Amira Eltony
- Wellman Center for Photomedicine - Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Theo Seiler
- Institut für Refraktive und Ophthalmo-Chirurgie (IROC), Zürich, Switzerland
| | - Seok-Hyun Yun
- Wellman Center for Photomedicine - Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA
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Seiler TG, Batista A, Frueh BE, Koenig K. Riboflavin Concentrations at the Endothelium During Corneal Cross-Linking in Humans. ACTA ACUST UNITED AC 2019; 60:2140-2145. [DOI: 10.1167/iovs.19-26686] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Affiliation(s)
- Theo G. Seiler
- Universitätsklinik für Augenheilkunde, Inselspital, Universität Bern, Bern, Switzerland
- Institut für Refraktive und Ophthalmo-Chirurgie (IROC), Zürich, Switzerland
- Wellman Center for Photomedicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States
| | - Ana Batista
- JenLab GmbH, Berlin, Germany
- Lehrstuhl für Biophotonik und Lasertechnologie, Universität des Saarlandes, Saarbrücken, Germany
| | - Beatrice E. Frueh
- Universitätsklinik für Augenheilkunde, Inselspital, Universität Bern, Bern, Switzerland
| | - Karsten Koenig
- JenLab GmbH, Berlin, Germany
- Lehrstuhl für Biophotonik und Lasertechnologie, Universität des Saarlandes, Saarbrücken, Germany
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Effect of freezing and thawing on the biomechanical characteristics of porcine ocular tissues. J Biomech 2019; 87:93-99. [PMID: 30876736 DOI: 10.1016/j.jbiomech.2019.02.024] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2018] [Revised: 12/25/2018] [Accepted: 02/23/2019] [Indexed: 12/13/2022]
Abstract
PURPOSE To evaluate the effect of freezing and thawing on the biomechanical properties of ex-vivo porcine ocular tissue. METHODS Thirty-six porcine eyes (18 pairs) were obtained fresh from a local abattoir and split into two groups of nine pairs to study the effect of storage at -20 °C and -80 °C. A randomly-selected eye from each pair (Control Group, CG) was tested fresh while the fellow eyes were frozen for 14 days, either at -20 °C and -80 °C (Frozen Group, FG) before thawing and testing. Seventy-two strips were extracted from the corneas and scleras of eye globes and subjected to uniaxial tension tests under loads up to 1.0 N. Following five preconditioning cycles, the load and elongation data obtained experimentally were analysed to derive the tissue's stress-strain and tangent modulus-strain behaviour. RESULTS Corneal tissue subjected to freezing at -20 °C exhibited significant increases in tangent modulus (mechanical stiffness) by 13 ± 17% (p = 0.003) at 1% strain and 14 ± 12% (p < 0.001) at 2% strain. In contrast, the increases in corneal stiffness at -80 °C were insignificant (6 ± 14%, p = 0.099 at 1% strain, 6 ± 15%, p = 0.091 at 2% strain). The corresponding increases in tangent modulus in the sclera were all insignificant (for -20 °C: 4 ± 14%, p = 0.265 at 1% strain, 3 ± 9%, p = 0.186 at 2% strain; for -80 °C: 3 ± 18%, p = 0.537 at 1% strain and 3 ± 18%, p = 0.491 at 2% strain). CONCLUSIONS The study provided evidence that freezing and thawing led to insignificant changes in ocular tissue stiffness except in corneal tissue that was frozen at -20 °C.
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