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Effect of hydration state and storage media on corneal biomechanical response from in vitro inflation tests.

PURPOSE
To evaluate corneal deformation with varying intraocular pressure and the dependency of the biomechanical response on the corneal hydration state, modulated by the storage solutions or postmortem period.


METHODS
Thirty fresh enucleated porcine eyes were used for in vitro whole eye globe inflation experiments. The eyes were separated into five groups and treated with different solutions: 20% dextran, 8% dextran, 0.125% riboflavin-20% dextran, Optisol-GS (Bausch & Lomb, Rochester, NY), and one control group of virgin (untreated) eyes. Intraocular pressure was increased (from 15 to 55 mm Hg) and decreased (to 15 mm Hg) in 5-mm Hg steps and Scheimpflug images were taken at each step. Measurements were repeated after 24 hours. Thickness and curvature changes were analyzed as a function of intraocular pressure.


RESULTS
Corneal deformation differed across conditions and hydration states. Dehydration by any dextran solution increased the hysteresis after the inflation/deflation cycle (14.29 vs 22.07 to 41.75 μm), whereas overnight hydration did not lead to a significant difference. Compared to control corneas, corneas treated with Optisol-GS showed the most similar behavior. Corneas treated with 0.125% riboflavin-20% dextran deformed most (Δthickness(max) = 38.27 μm), indicating a softening of the corneal tissue compared to control corneas (23.18 μm) and corneas treated with 8% dextran (21.01 μm) and 20% dextran (29.07 μm). Dextran instillation decreased corneal thickness on average to 56.5% at 0 hours and 72.7% at 24 hours.


CONCLUSIONS
Corneal hydration and tissue preservation changed corneal biomechanics, in particular its relaxation over a period of 24 hours.