Corneal Crosslinking With Rose Bengal and Green Light: Efficacy and Safety Evaluation

Purpose: To evaluate crosslinking of cornea in vivo using green light activation of Rose Bengal (RGX) and assess potential damaging effects of the green light on retina and iris. Methods: Corneas of Dutch belted rabbits were de-epithelialized, then stained with Rose Bengal and exposed to green light, or not further treated. Corneal stiffness was measured by uniaxial tensiometry. Re-epithelialization was assessed by fluorescein fluorescence. Keratocytes were counted on hematoxylin and eosin (H&E)-stained sections, and iris cell damage was assessed by lactate dehydrogenase staining. Thermal effects on the blood-retinal barrier (BRB) were assessed by fluorescein angiography and those on photoreceptors, retinal pigment epithelium (RPE), and choriocapillaris by light microscopy and transmission electron microscopy. Results: RGX (10-min irradiation; 150 J/cm(2)) increased corneal stiffness 1.9-fold on day 1 (1.25 +/- 0.21 vs. 2.38 +/- 0.59 N/mm; P = 0.036) and 2.8-fold compared with controls on day 28 (1.70 +/- 0.74 vs. 4.95 +/- 1.86 N/mm; P = 0.003). Keratocytes decreased only in the anterior stroma on day 1 (24.0 +/- 3.0 vs. 3.67 +/- 4.73, P = 0.003) and recovered by day 28 (37.7 +/- 8.9 vs. 34.5 +/- 2.4, P = 0.51). Iris cells were not thermally damaged. No evidence of BRB breakdown was detected on days 1 or 28. Retina from RGX-treated eyes seemed normal with RPE cells showing intact nuclei shielded apically by melanosomes, morphologically intact photoreceptor outer segments, normal outer nuclear layer thickness, and choriocapillaris containing intact erythrocytes. Conclusions: The substantial corneal stiffening produced by RGX together with the lack of significant effects on keratocytes and no evidence for retina or iris damage suggest that RGX-initiated corneal crosslinking may be a safe, rapid, and effective treatment.