Corneal Curvature and Thickness Ater Treatment Wth UVA and Riboflavin Assessed by Optical Coherence Tomography

Abstract

Purpose: : To quantify changes in curvature, asphericity and thickness induced in Eye-Bank corneas after cross-linking treatment with ultraviolet light and riboflavin.

Methods: : Two human cadaver eyes (one pair, 79 years old, 2 days postmortem) were used. The corneal thickness was restored to normal values by placing the whole globe, cornea side down, in 25% Dextran for 24 hours. The eyes were re-inflated to normal pressures by injecting 25% Dextran in the posterior chamber. Re-inflation does not significantly alter the corneal shape between 2mmHg and 140mmHg (Brenman et al, 2000). The epithelium was removed from both the eyes using alcohol and a cotton swap. The whole globes were imaged with a custom-built laboratory optical coherence tomography system. After images were acquired, one drop of 0.1% riboflavin solution (10mg riboflavin-5-phosphate in 10mL Dextran 20% solution) was placed on the cornea every 5 minutes for 30 minutes. The cornea was then irradiated for 30 minutes using UVA radiation at 378nm with an irradiance of 3mW/cm². To maintain hydration of the cornea during irradiation, one drop of riboflavin solution was placed on the cornea every 5 minutes. The whole globes were imaged after treatment with the optical coherence tomography system. The anterior corneal surface profile was extracted from the images and the central 5mm was fit with a conic section to calculate curvature and asphericity. The central corneal thickness was calculated by dividing the optical distance between the signal peaks of the central A-line by 1.38.

Results: : Treatment with ultraviolet light and riboflavin results in a decrease in corneal curvature (6.98mm before versus 5.74mm after treatment; 6.20mm before versus 5.23mm after treatment), an increase in asphericity magnitude (-1.76 before versus -8.34 after treatment; -8.87 before versus -16.46 after treatment), and a decrease in thickness (476µm before versus 402µm after treatment; 431µm before versus 394µm treated).

Conclusions: : These results suggest that corneal crosslinking produces a steepening and thinning of the cornea.Support: IMSD (JD); Florida Lions Eye Bank; NIH center grant P30-EY014801; Research to Prevent Blindness; Henri and Flore Lesieur Foundation (JMP).

Keywords: keratoconus • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)