Rose Bengal-Green Light for Collagen Cross-linking.

Wollensak et al reported the first application of corneal cross-linking (CXL) for the treatment of keratoconus in 2003.[1] Thereafter, many articles were published regarding the efficacy of CXL to halt the progression of keratoconus. Long-term studies have shown its success rate ranging from 78% to 100%.[23] Two studies evaluated the effect of CXL on decreasing the number for keratoplasty procedures in patients with keratoconus. Dutch Transplant Registry showed a significant decrease in the need for keratoplasty after implementation of CXL.[4] Another study showed that the need of keratoplasty for keratoconus is halved mostly due to the effect of CXL.[5]

Although many modifications in CXL have been introduced over a decade from epithelium-on to accelerated CXL to improve its outcomes, CXL has its own complications and limitations. One of the most daunting complications of CXL is endothelial decompensation that has been reported in some cases.[6] Patients with thin cornea are more susceptible to this complication due to the reduced barrier effect of riboflavin-saturated stroma against penetrance of ultraviolet (UV) light. Some techniques, such as hypoosmolar riboflavin and contact lens-assisted CXL, have been introduced to circumvent this problem.[78] Moreover, Hafezi reported CXL failure in corneas with stromal thickness less than 330 μm.[9]

Cherfan et al developed corneal CXL using rose bengal with green light (RGX) instead of UV light.[10] In their study, they showed that application of RGX for 12 min increased corneal stiffness by 3.8-fold. Cross-linked stroma was limited to anterior 100–120 μm of the cornea without any toxicity to stromal keratocytes. There is no photo-sensitized toxicity of endothelial cells in this technique because rose bengal penetrates only the anterior stroma. Recently, corneal biomechanical changes after UV-CXL and RGX were evaluated in rabbit eyes by using Corvis ST (Oculus, Wetzlar, Germany).[11] The study showed that stiffness of the treated stroma increased by 11-fold and 6.25-fold after RGX and UV-CXL, respectively. Therefore, although RGX treats only 100-μm of the anterior stroma, it has a stronger effect than UV-CXL. However, another study reported a non-significant change in Young's modulus of the cornea after RGX treatment.[12]

Infectious keratitis may be considered as another possible application of RGX. RGX-treated corneas are more resistant to collagenase digestion.[13] Further, in contrast to UV-CXL, RGX not only arrests the growth of methicillin-resistant Staphylococcus aureus (MRSA) strain cultures, similar to riboflavin plus UV, but also inhibits the growth of fungal cultures.[1415] Although the primary results of these in-vitro studies are promising, further studies are needed to evaluate the efficacy and safety of RGX. This technique may be added to our armamentarium for the treatment of corneal diseases, especially keratoconic thin cornea and infectious keratitis.

Financial Support and Sponsorship

Nil.

Conflicts of Interest

There are no conflicts of interest.