Purpose: To evaluate the importance of complete epithelial removal before riboflavin-ultraviolet-A (UVA) corneal collagen crosslinking therapy.
Setting: School of Optometry and Vision Sciences, Cardiff University, Wales, United Kingdom.
Methods: Riboflavin eyedrops were applied at 5-minute intervals for 35 minutes to the anterior corneal surface of 36 porcine eyes (12 with no epithelial trauma but treated with tetracaine eyedrops, 12 with superficial epithelial trauma but with an intact basal epithelium, and 12 with a fully removed epithelium). The corneal surface of 6 tetracaine-treated eyes, 6 eyes with superficial epithelial trauma, and 6 eyes with a fully removed epithelium was exposed to UVA light for 30 minutes during riboflavin administration. The light transmission spectra of the enucleated corneas were analyzed with a spectrophotometer and compared with those of 9 untreated porcine corneas.
Results: Corneas with a fully removed epithelium treated with riboflavin showed an abnormal dip in the transmission spectrum between 400 nm and 510 nm (P<.01). This was attributed to the presence of riboflavin in the corneal stroma. The spectra of riboflavin-treated corneas with no epithelial trauma but tetracaine administration and those with superficial epithelial trauma did not differ from those of the non-riboflavin-treated controls. Exposure to UVA following riboflavin administration did not alter corneal light transmission.
Conclusions: Complete removal of the corneal epithelium is an essential component of riboflavin-UVA crosslinking therapy as superficial epithelial trauma and tetracaine administration alone are not sufficient to permit the penetration of riboflavin into the corneal stroma. Failure to achieve adequate stromal absorption of riboflavin may impair the efficacy of the crosslinking process.