Rose bengal and green light versus riboflavin–UVA cross-linking: Corneal wound repair response

Abstract

Purpose: To study corneal wound healing after two cross-linking techniques using either rose bengal and green light (RGX) or the conventional treatment using riboflavin and UVA radiation (UVX). Methods: Corneas of New Zealand rabbits were monolaterally treated with UVX (21 eyes) or RGX (25 eyes). Treatments involved corneal de-epithelialization (8-mm diameter), soaking with photosensitizer (0.1% riboflavin in 20% dextran for 30 minutes for UVX; 0.1% rose bengal for 2 minutes for RGX), and light irradiation (370 nm, 3 mW/cm2, 30 minutes for UVX; 532 nm, 0.25 W/cm2, 7 minutes for RGX). Contralateral eyes were used as controls. Clinical follow-up included fluorescein staining, haze measurement, and pachymetry. Healing events analyzed after euthanasia at 2, 30, and 60 days included cell death (TUNEL assay), cell proliferation (BrdU [bromodeoxyuridine] immunofluorescence), and differentiation to myofibroblasts (α-SMA [alpha smooth muscle actin] immunohistochemistry). Results: Re-epithelialization and pachymetries were similar after RGX and UVX. The haze from day 1 to 15 was greater after UVX. Cell death was deeper after UVX, being localized in the anterior and middle stroma, and was superficial (anterior third) after RGX. Cell proliferation appeared after 2 days and was localized in the middle and posterior stroma in the UVX group but was superficial in the RGX group. After 60 days the number of stromal cells had not returned to the control number in either group. Conclusions: The deeper and longer-lasting cell damage caused by UVX compared to RGX may underlie the slower cell repopulation after UVX and other differences in healing. Shallower damage and a shorter treatment time suggest that RGX may be appropriate for stiffening thin corneas.