Use of Ultraviolet Cross-Linking for the Treatment of Thin Corneas in Keratoconus

Ultraviolet cross-linking of corneal collagen is an innovative technique designed to increase corneal strength in keratoconus by creating additional cross-links within the macromolecules of the extracellular matrix. The method is based on exposing the cornea to ultraviolet A radiation (370 nm) after saturation of the stroma with a photosensitizer (riboflavin). In the standard (Dresden) protocol—the conventional method of ultraviolet cross-linking—the minimum thickness of the de-epithelialized cornea must be at least 400 μm to prevent potential endothelial cell damage from a cytotoxic dose of ultraviolet radiation. However, in some patients with keratoconus, corneal thickness falls below this threshold, which limits the applicability of the standard clinical protocol. As a result, modified cross-linking techniques have been proposed for patients with thin corneas. This review presents various approaches developed to address this issue. In general, the safety and efficacy of modified techniques, including transepithelial, accelerated, intraoperative hypoosmotic swelling ones, or techniques involving contact lenses or donor corneal lens, have shown satisfactory outcomes: in most cases, corneal ectasia progression can be halted without serious postoperative complications. Nevertheless, each technique has its own advantages and limitations. The choice of technique depends on the resources of the clinic, the individual characteristics of the patient’s cornea, and the surgeon’s expertise. It should be noted that in practice modified cross-linking protocols for thin corneas are used much less frequently than the standard procedure, underscoring the need for further research to evaluate their clinical efficacy and safety.