Effects of ultraviolet corneal cross-linking upon the limbus. Literature review

Today, corneal ultraviolet (UV) collagen cross-linking (CXL) appears to be the most effective and preferable technology for treating keratectasia. CXL is a simple, minimally invasive procedure, therefore, it has become the most reliable treatment for corneal degeneration, compared to other surgical modalities. In the vast majority of cases, CXL provides good clinical and functional outcomes and remains the safest technique for the treatment of corneal degenerations. The data from experimental studies and clinical observations indicate the potential of developing CXL-induced damage to the limbal niche structures. This process contributes to the development of cytotoxicity, stimulates apoptosis, reduces cell proliferation and can result in delayed cellular mutations. It is necessary to protect corneal limbus from undesired UV exposure during CXL. This can be achieved by forming the required diameter of the UV spot (8–9 mm), and by using filters or protective rings that prevent UV rays from reaching the corneal periphery. There is still a need for long-term experimental and clinical studies on the effect of UVA radiation on sensitive limbal structures in order to adjust CXL protocols and minimize the risk of possible complications.