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Bola Ayoub Gawargious, Alan Le, Michael Lesgart, Shoaib Ugardar, Joseph L Demer; Differential Regional Stiffening of Sclera by Collagen Cross-linking. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4359.
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Corneal collagen cross-linking by activating riboflavin with UV-A light is been used clinically to enhance corneal stiffness. In mammals, sclera contains approximately 50% collagen by weight and therefore can be stiffened similarly. While previous studies investigated the effects of scleral cross-linking in animals and humans irrespective of specific scleral location, we sought to determine if cross-linking has regionally differential effects.
Scleral strips were excised from 12 unfixed human cadaver eyes. Parallel adjacent strips of sclera measuring 2x8mm were trimmed by scalpel from 4 quadrants (superlateral, supermedial, inferolateral, inferomedial) in the posterior and equatorial sclera. One strip of each pair was used as a control while the other was submerged in 0.1% riboflavin for 30 minutes then exposed to 365 nm UV-A at 6mW/cm2 for 30 minutes to achieve cross-linking. Strips were mechanically characterized using a horizontally mounted microtensile load cell with in-line strain gauge attached to a linear motor. Optical coherence tomography was used to measure specimen cross-sectional area before and after crosslinking.
Young’s modulus (YM), a measure of deformation in response to tension, was calculated at 8% strain for all specimens. After cross-linking, mean (±SEM) YM in each of the four posterior quadrants (superlateral, supermedial, inferolateral, inferomedial) increased significantly by 46±15%, 32±11%, 67±20%, and 53±11%, respectively (P<0.001). There was also a significant increase in YM in each of the respective the four equatorial quadrants at 139± 43%, 68±27%, 143±92%, and 68±14%, respectively. Pooling all quadrants, scleral volume after cross linking was reduced 17±1% in the equatorial and 13±1% in posterior sclera (P<0.001). Correlation analysis indicated that ~90% of the volume reduction was due to thickness reduction, with little change in length.
Collagen cross-linking has a topographically differential effect on YM of human sclera. In general, cross linking increases YM more in the equatorial than posterior sclera, and most in the superolateral equatorial region. The particularly great effect of crosslinking in this region might potentially be useful as a treatment, since staphylomata are prone to form superotemporally in progressive myopia.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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