Interaction of ultraviolet light with the cornea: clinical implications for corneal crosslinking
Understanding ultraviolet (UV) interaction with the human corneal tissue is of interest among corneal specialists given the widespread application of corneal crosslinking. We review the current knowledge of light interaction with the cornea in the UV wavelength range and use a novel experimental study to illustrate the role of 2 important corneal properties that have not yet been clarified: the epithelial contribution to overall UVA corneal absorbance and the regional anisotropy of UVA light transmittance. Finally, we present the most recent insights into how different methods of UVA light irradiation and corneal soaking with riboflavin influence the outcome of corneal crosslinking.
M. Lombardo, G. Pucci, R. Barberi, G. Lombardo. Interaction of ultraviolet light with the cornea: Clinical implications for corneal crosslinking. J. Cataract Refract. Surg. 41(2):446-459 (2015). full text
M. Lombardo, N. Micali, V. Villari, S. Serrao, G. Pucci, R. Barberi, G. Lombardo. Ultraviolet A: Visible spectral absorbance of the human cornea after transepithelial soaking with dextran-enriched and dextran-free riboflavin 0.1% ophthalmic solutions. J. Cataract Refract. Surg. 41(10):2283-2290 (2015). full text
Ultraviolet A: Visible spectral absorbance of the human cornea after transepithelial soaking with dextran-enriched and dextran-free riboflavin 0.1% ophthalmic solutions
To evaluate the stromal concentration of 2 commercially available transepithelial riboflavin 0.1% solutions in human donor corneas with the use of spectrophotometry.
The absorbance spectra of 12 corneal tissues were measured in the 330 to 700 nm wavelength range using a purpose-designed spectrophotometry setup before and after transepithelial corneal soaking with a 15% dextran-enriched riboflavin 0.1% solution (n = 6) or a hypotonic dextran-free riboflavin 0.1% solution (n = 6). Both ophthalmic solutions contained ethylenediaminetetraacetic acid and trometamol as enhancers. In addition, 4 deepithelialized corneal tissues underwent stromal soaking with a 20% dextran-enriched riboflavin 0.1% solution and were used as controls. All the riboflavin solutions were applied topically for 30 minutes. The stromal concentration of riboflavin was quantified by analysis of absorbance spectra of the cornea collected before and after application of each solution.
The mean stromal riboflavin concentration was 0.012% ± 0.003% (SD), 0.0005% ± 0.0003% (P < .001), and 0.004% ± 0.001% (P < .01) in tissues soaked with 20% dextran-enriched, 15% dextran-enriched, and hypotonic dextran-free solutions, respectively. The difference of stromal riboflavin concentration between the 2 transepithelial solutions was statistically significant (P < .01).
Dextran-enriched solutions required complete corneal deepithelialization to permit effective stromal soaking with riboflavin. Nevertheless, riboflavin in hypotonic dextran-free solution with enhancers permeates across stroma through an intact epithelium.