Effect of epithelial retention and removal on riboflavin absorption in porcine corneas.

PURPOSE To compare stromal riboflavin absorption after 20% alcohol application and partial or complete epithelial removal by analyzing light transmission properties of porcine corneas after riboflavin/ultraviolet A (UVA) corneal collagen cross-linking. METHODS Riboflavin 0.13% eye drops were applied to 18 porcine eyes (6 in which 20% alcohol solution had been applied for 40 seconds, 6 eyes with a grid pattern of full-thickness epithelial trauma, and 6 with the central epithelium fully removed) at 5-minute intervals for 35 minutes. In all eyes, the corneal surface was exposed to UVA light for 30 minutes during riboflavin administration. The light transmission spectra of the corneas were analyzed with a spectrophotometer and compared to those of 9 untreated controls (4 corneas with epithelium and 5 without) and to the spectra of riboflavin 0.13% solution. RESULTS The spectra of riboflavin-treated corneas in the alcohol group were similar to controls. Those with grid-pattern epithelial trauma showed a dip in light transmission between 400 and 490 nm, but this was significantly less than that in eyes for which epithelial removal was complete, where the spectrum was similar to that of riboflavin 0.13% solution. CONCLUSIONS Complete removal of the corneal epithelium appears to be necessary to allow sufficient riboflavin absorption into the stroma to alter the normal light transmission properties of the porcine cornea. Although partial grid-pattern epithelial removal allows some riboflavin penetration, uptake is limited and non-homogeneous, which may affect the efficacy of the cross-linking process.