Abstract
Purpose :
To examine corneal thinning and refractive index change in ex vivo bovine eyes during Corneal Collagen Cross-Linking (CXL) using 365-nm UVA irradiation and riboflavin as a photosensitizer – a newly emerging treatment paradigm for corneal ectatic disorders.
Methods :
Eyes were prepared for the CXL procedure based on the standard protocol that includes removal of the corneal epithelium to facilitate diffusion of riboflavin into the stroma. Corneal stromal thickness and group refractive index (GRI) were monitored during CXL by a 1310-nm optical coherence tomography (OCT) imaging system integrated with an optical path length method. Measurements were performed at three critical points: immediately after removal of corneal epithelium; after 30-minute riboflavin instillation; and after 30-minute UVA irradiation with continuing riboflavin instillation.
Results :
Group refractive index (GRI) of the bovine cornea changed significantly from epithelial removal to riboflavin instillation and UVA irradiation, increasing from 1.377±0.005 (mean ± standard deviation) after de-epithelization to 1.387±0.003 after 30-min instillation and 1.388±0.008 after subsequent irradiation. The de-epithelized bovine corneas also underwent considerable decrease (10-20%) in corneal stromal thickness with thinning of 95±29 µm (mean ± standard deviation) after riboflavin instillation and further decrease (~5%) with thinning of 42±19 µm after UVA irradiation.
Conclusions :
It is important to monitor corneal thickness change during CXL especially after riboflavin instillation when the decrease is largest, to avoid delivering endothelial cytotoxic doses especially for patients with thin corneas. Increase in refractive index heightens the concern about corneal thinning and the need for careful monitoring as a safety precaution.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.