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      Individualized Characterization of the Distribution of Collagen Fibril Dispersion Using Optical Aberrations of the Cornea for Biomechanical Models

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          Abstract

          Purpose

          The spatial distribution of collagen fibril dispersion has a significant impact on both corneal biomechanical and optical behaviors. The goal of this study was to demonstrate a novel method to characterize collagen fibril dispersion using intraocular pressure (IOP)-induced changes in corneal optical aberrations for individualized finite-element (FE) modeling.

          Methods

          The method was tested through both numerical simulations and ex vivo experiments. Inflation tests were simulated in FE models with three assumed patterns of collagen fibril dispersion and experimentally on three rhesus monkey corneas. Geometry, matrix stiffness, and the IOP-induced changes in wavefront aberrations were measured, and the collagen fibril dispersion was characterized. An individualized corneal model with customized collagen fibril dispersion was developed, and the estimated optical aberrations were compared with the measured data.

          Results

          For the theoretical investigations, three assumed distributions of fibril dispersion were all successfully characterized. The estimated optical aberrations closely matched the measured data, with average root-mean-square (RMS) differences of 0.29, 0.24, and 0.10 µm for the three patterns, respectively. The overall features of the IOP-induced changes in optical aberrations were estimated for two ex vivo monkey corneas, with average RMS differences of 0.57 and 0.43 µm. Characterization of the fibril dispersion in the third cornea might have been affected by corneal hydration, resulting in an increased RMS difference, 0.8 µm.

          Conclusions

          A more advanced corneal model with individualized distribution of collagen fibril dispersion can be developed and used to improve our ability to understand both biomechanical and optical behaviors of the cornea.

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          Most cited references63

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          Changes in collagen orientation and distribution in keratoconus corneas.

          To map the collagen orientation and relative distribution of collagen fibrillar mass in keratoconus corneal buttons. Structural analysis was performed by obtaining synchrotron x-ray scattering patterns across the samples at 0.25-mm intervals. The patterns were analyzed to produce two-dimensional maps of the orientation of the lamellae and of the distribution of total and preferentially aligned lamellae. Compared with normal corneas, in keratoconus the gross organization of the stromal lamellae was dramatically changed, and the collagen fibrillar mass was unevenly distributed, particularly around the presumed apex of the cone. The development of keratoconus involves a high degree of inter- and probably intralamellar displacement and slippage that leads to thinning of the central cornea and associated changes in corneal curvature. This slippage may be promoted by a loss of cohesive forces and mechanical failure in regions where lamellae bifurcate.
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            Biomechanical properties of keratoconus and normal corneas.

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              The three-dimensional organization of collagen fibrils in the human cornea and sclera.

              The organization of collagen fibrils in the human cornea and sclera was studied by scanning electron microscopy, after digestion of cellular elements by sodium hydroxide, and by conventional transmission electron microscopy. The collagen fibrils in the cornea had a uniform diameter of about 25 nm. In Bowman's layer, individual collagen fibrils were interwoven densely to form a felt-like sheet. In the stroma, most of the collagen fibrils ran abreast in lamellae, with varying widths and thickness. These lamellae were arranged basically parallel to the corneal surface but often communicated with those of adjacent layers by interchanging their fibrils. In the innermost stromal region adjacent to Descemet's membrane, collagen fibrils were oriented in various directions and interlaced, forming loose fibrillar networks. The sclera, however, was composed of collagen fibrils with various diameters ranging from 25-230 nm. Although these collagen fibrils formed bundles, they were not parallel but were entangled in individual bundles. These collagen bundles varied in width and thickness, often gave off branches, and intertwined with each other.
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                Author and article information

                Journal
                Invest Ophthalmol Vis Sci
                Invest. Ophthalmol. Vis. Sci
                iovs
                IOVS
                Investigative Ophthalmology & Visual Science
                The Association for Research in Vision and Ophthalmology
                0146-0404
                1552-5783
                31 August 2020
                August 2020
                : 61
                : 10
                : 54
                Affiliations
                [1 ]Department of Mechanical Engineering, University of Rochester, Rochester, New York, United States
                [2 ]Department of Biomedical Engineering, University of Rochester, Rochester, New York, United States
                [3 ]Flaum Eye Institute, The Institute of Optics, Center for Visual Science, Department of Biomedical Engineering, University of Rochester, Rochester, New York, United States
                Author notes
                [* ]Correspondence: Geunyoung Yoon, Flaum Eye Institute, University of Rochester, 601 Elmwood Avenue, Rochester, NY 14642, USA; gyoon@ 123456ur.rochester.edu .
                Article
                IOVS-20-29573
                10.1167/iovs.61.10.54
                7463181
                32866268
                cc982e65-70db-40ea-9f05-1f73a244f22a
                Copyright 2020 The Authors

                This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

                History
                : 22 July 2020
                : 27 February 2020
                Page count
                Pages: 14
                Categories
                Cornea
                Cornea

                collagen fibrils,corneal biomechanics,optical aberrations,biomechanical models

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