Efficacy of Rose Bengal as a Light Activated Cross-Linker in Guinea Pig Sclera

Abstract

Purpose : High myopia is a severe form of myopia that currently affects 400 million people, and is predicted to affect 938 million by 2050. High myopia can cause staphyloma and blindness. It arises from scleral remodelling, in which there is a reduction in collagen bonds, weakened cross-links, thinning and abnormal scleral elasticity. A possible treatment involves light-activated cross-linking to strengthen the sclera. We compared the efficacy of two different photosensitisers: Riboflavin (R) activated by ultraviolet light (UVA) and Rose Bengal (RB), activated by green light (RGX).

Methods : Scleral punches (diameter 4 mm, 140 µm thick, n=52) were made in the posterior pole region in freshly dissected guinea pig eyes. Punches were soaked in: R (0.1% Sigma, R 4500), RB (0.1, 0.01 or .001%) or control solution (Phosphate Buffered Saline, PBS) at pH 7.4 for times between 2 mins and 24 hrs. After soaking, tissues were irradiated for 2x15 mins under UVA light for R (365 nm, 2.4 mW/cm²), green light for RG (532 nm, 1.8 mW/cm²), or no irradiation. A modified heat sensitive assay was used to determine tissue denaturation and shrinkage properties between 40-80°C.

Results : R/UVA produced a 1.7⁰C protective temperature shift for 24 hr soak times relative to both UVA and PBS alone. RGX produced a greater protective shift for soak times as short as 2 mins relative to PBS (3.3⁰C). The degree of induced RGX was not enhanced with longer soak times. For 2 min soaks, there was no difference between 0.01% and 0.1% concentrations in RGX efficacy. In general the protection of the sclera from temperature denaturation was independent of the concentration of RB unless greater than 1% where efficacy reduced.

Conclusions : RGX showed greater efficacy at lower concentrations with shorter exposure times than R/UVA, mirroring biomechanics found in treated cornea.¹ The insensitivity of RB to dose may reflect complexes forming between RB and scleral collagen components, as proposed for epithelialized cornea.² The diffusion profile of RB may also avoid the phototoxic loss of keratocytes observed with R/UVA arising from insufficient riboflavin accumulation. Local application of RB is unlikely to penetrate into adjacent tissues, and its effacacy suggests RGX will strengthen the sclera, and may protect very high myopia subjects from developing staphyloma and blindness.
1. Bekesi N, et al. IOVS 2016;57:992-1001.
2. Cherfan D, et al. IOVS 2013;54:3426–3433.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.