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      Dynamic OCT measurement of corneal deformation by an air puff in normal and cross-linked corneas

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          Abstract

          A new technique is presented for the non-invasive imaging of the dynamic response of the cornea to an air puff inducing a deformation. A spectral OCT instrument combined with an air tonometer in a non-collinear configuration was used to image the corneal deformation over full corneal cross-sections, as well as to obtain high speed measurements of the temporal evolution of the corneal apex. The entire deformation process can be dynamically visualized. A quantitative analysis allows direct extraction of several deformation parameters, such as amplitude, diameter and volume of the maximum deformation, as well as duration and speed of the increasing deformation period and the recovery period. The potential of the technique is demonstrated on porcine corneas in vitro under constant IOP for several conditions (untreated, after riboflavin instillation and under cross-linking with ultraviolet light), as well as on human corneas in vivo. The new technique has proved very sensitive to detect differences in the deformation parameters across conditions. We have confirmed non-invasively that Riboflavin and UV-cross-linking induce changes in the corneal biomechanical properties. Those differences appear to be the result of changes in constituent properties of the cornea, and not a consequence of changes in corneal thickness, geometry or IOP. These measurements are a first step for the estimation of the biomechanical properties of corneal tissue, at an individual level and in vivo, to improve diagnosis and prognosis of diseases and treatments involving changes in the biomechanical properties of the cornea.

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          Most cited references37

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          Determining in vivo biomechanical properties of the cornea with an ocular response analyzer.

          David Luce (2005)
          To study the results of an ocular response analyzer (ORA) to determine the biomechanical properties of the cornea and their relationship to intraocular pressure (IOP). Reichert Inc., Depew, New York, USA. The ORA (Reichert) makes 2 essentially instantaneous applanation measurements that permit determination of corneal and IOP effects. Measurements of several populations indicate that corneal hysteresis, a biomechanical measure, varied over a dynamic range of 1.8 to 14.6 mm Hg and was only weakly correlated with corneal thickness (r(2)=0.12); this is related to the observation that some subjects with relatively thick corneas have less-than-average corneal hysteresis. Corneal hysteresis changes diurnally, presumably as a result of hydration changes. Keratoconus, Fuchs' dystrophy, and post-LASIK patients demonstrated low corneal hysteresis. The corneal hysteresis biomechanical measure may prove valuable for qualification and predictions of outcomes of refractive surgery and in other cases in which corneal biomechanics are important.
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            Riboflavin/ultraviolet-a–induced collagen crosslinking for the treatment of keratoconus

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              Stress-strain measurements of human and porcine corneas after riboflavin-ultraviolet-A-induced cross-linking.

              To evaluate the biomechanical effect of combined riboflavin-ultraviolet A (UVA) treatment on porcine and human corneas. Department of Ophthalmology, Technical University of Dresden, Dresden, Germany. Corneal strips from 5 human enucleated eyes and 20 porcine cadaver corneas were treated with the photosensitizer riboflavin and irradiated with 2 double UVA diodes (370 nm, irradiance = 3 mW/cm2) for 30 minutes. After cross-linking, static stress-strain measurements of the treated and untreated corneas were performed using a microcomputer-controlled biomaterial tester with a prestress of 5 x 10(3) Pa. There was a significant increase in corneal rigidity after cross-linking, indicated by a rise in stress in treated porcine corneas (by 71.9%) and human corneas (by 328.9%) and in Young's modulus by the factor 1.8 in porcine corneas and 4.5 in human corneas. The mean central corneal thickness was 850 microm +/- 70 (SD) in porcine corneas and 550 +/- 40 microm in human corneas. Riboflavin-UVA-induced collagen cross-linking led to an increase in mechanical rigidity in porcine corneas and an even greater increase in human corneas. As collagen cross-linking is maximal in the anterior 300 microm of the cornea, the greater stiffening effect in human corneas can be explained by the relatively larger portion of the cornea being cross-linked in the overall thinner human cornea.
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                Author and article information

                Journal
                Biomed Opt Express
                BOE
                Biomedical Optics Express
                Optical Society of America
                2156-7085
                09 February 2012
                01 March 2012
                09 February 2012
                : 3
                : 3
                : 473-487
                Affiliations
                [1]Instituto de Optica, Consejo Superior de Investigaciones Científicas (CSIC), Serrano 121, 28006 Madrid, Spain
                Author notes
                Article
                159961
                10.1364/BOE.3.000473
                3296536
                22435096
                802b7480-01c9-4a50-9f27-b19ed26703ad
                ©2012 Optical Society of America

                This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 Unported License, which permits download and redistribution, provided that the original work is properly cited. This license restricts the article from being modified or used commercially.

                History
                : 13 December 2011
                : 17 January 2012
                : 17 January 2012
                Funding
                Funded by: Spanish Ministry of Science and Innovation
                Award ID: FIS2008-02065
                Award ID: FIS2011-25637
                Funded by: EURHORCs-ESF EURYI
                Award ID: 05-102-ES
                Award ID: ERC-2011-AdG294099
                Categories
                Ophthalmology Applications
                Custom metadata
                True
                0

                Vision sciences
                (170.3880) medical and biological imaging,(170.4500) optical coherence tomography,(330.5370) physiological optics,(330.4460) ophthalmic optics and devices,(170.4470) ophthalmology

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