Corneal Collagen Crosslinking Techniques: Updates

Corneal collagen crosslinking (CXL) is usually practiced on keratoconic corneas to strengthen the corneal biomechanical structure. The conventional CXL procedure, with riboflavin and ultraviolet A (UVA), initially involves corneal de-epithelialization to allow riboflavin penetration into the stroma. Discomfort and complications are related to this corneal debridement. Thus, transepithelial CXL has emerged to substitute for the conventional method. This technique preserves the epithelium and tends to ensure the same efficiency of corneal stiffening. To allow riboflavin penetration through the epithelial barrier, several chemical modifications to riboflavin, such as addition of enhancers (EDTA, benzalkonium chloride or 20% alcohol), and osmolar modifications have been applied. The most studied transepithelial riboflavin is Ricrolin TE®, which combines two enhancers: amino alcohol and EDTA. The results of clinical studies have not demonstrated effectiveness yet. Moreover, the iontophoresis technique, a noninvasive procedure during which a low-intensity electric current is applied to enhance the penetration of riboflavin into the stroma, stands out as being as efficient as conventional application of riboflavin, based on a pre-clinical study. Another area of improvement of CXL is modification of the UVA irradiation profile or shortening of the UVA irradiation time while increasing the irradiation power. A longer follow-up and more investigations are still necessary to define the future of transepithelial CXL, but it is an exciting and rapidly evolving area.