Ciro Caruso1, Robert L Epstein, Carmine Ostacolo, Luigi Pacente, Salvatore Troisi, Gaetano Barbaro. 1. *Corneal Transplant Center, Pellegrini Hospital, Naples, Italy; †Mercy Center for Corrective Eye Surgery, McHenry, IL; ‡Department of Pharmacy, University of Naples Federico II, Naples, Italy; §Department of Ophthalmology, Pellegrini Hospital, Naples, Italy; ¶Department of Ophthalmology, Salerno University Hospital, Salerno, Italy; and ‖Institute of Refractive and Ophthalmic Surgery (IROS), Naples, Italy.
Abstract
PURPOSE: To improve the safety, reproducibility, and depth of effect of corneal cross-linking with the ultraviolet A (UV-A) exposure time and fluence customized according to the corneal thickness. METHODS: Twelve human corneas were used for the experimental protocol. They were soaked using a transepithelial (EPI-ON) technique using riboflavin with the permeation enhancer vitamin E-tocopheryl polyethylene glycol succinate. The corneas were then placed on microscope slides and irradiated at 3 mW/cm for 30 minutes. The UV-A output parameters were measured to build a new equation describing the time-dependent loss of endothelial protection induced by riboflavin during cross-linking, as well as a pachymetry-dependent and exposure time-dependent prescription for input UV-A fluence. The proposed equation was used to establish graphs prescribing the maximum UV-A fluence input versus exposure time that always maintains corneal endothelium exposure below toxicity limits. RESULTS: Analysis modifying the Lambert-Beer law for riboflavin oxidation leads to graphs of the maximum safe level of UV-A radiation fluence versus the time applied and thickness of the treated cornea. These graphs prescribe UV-A fluence levels below 1.8 mW/cm for corneas of thickness 540 μm down to 1.2 mW/cm for corneas of thickness 350 μm. Irradiation times are typically below 15 minutes. CONCLUSIONS: The experimental and mathematical analyses establish the basis for graphs that prescribe maximum safe fluence and UV-A exposure time for corneas of different thicknesses. Because this clinically tested protocol specifies a corneal surface clear of shielding riboflavin on the corneal surface during UV-A irradiation, it allows for shorter UV-A irradiation time and lower fluence than in the Dresden protocol.
PURPOSE: To improve the safety, reproducibility, and depth of effect of corneal cross-linking with the ultraviolet A (UV-A) exposure time and fluence customized according to the corneal thickness. METHODS: Twelve human corneas were used for the experimental protocol. They were soaked using a transepithelial (EPI-ON) technique using riboflavin with the permeation enhancer vitamin E-tocopheryl polyethylene glycol succinate. The corneas were then placed on microscope slides and irradiated at 3 mW/cm for 30 minutes. The UV-A output parameters were measured to build a new equation describing the time-dependent loss of endothelial protection induced by riboflavin during cross-linking, as well as a pachymetry-dependent and exposure time-dependent prescription for input UV-A fluence. The proposed equation was used to establish graphs prescribing the maximum UV-A fluence input versus exposure time that always maintains corneal endothelium exposure below toxicity limits. RESULTS: Analysis modifying the Lambert-Beer law for riboflavin oxidation leads to graphs of the maximum safe level of UV-A radiation fluence versus the time applied and thickness of the treated cornea. These graphs prescribe UV-A fluence levels below 1.8 mW/cm for corneas of thickness 540 μm down to 1.2 mW/cm for corneas of thickness 350 μm. Irradiation times are typically below 15 minutes. CONCLUSIONS: The experimental and mathematical analyses establish the basis for graphs that prescribe maximum safe fluence and UV-A exposure time for corneas of different thicknesses. Because this clinically tested protocol specifies a corneal surface clear of shielding riboflavin on the corneal surface during UV-A irradiation, it allows for shorter UV-A irradiation time and lower fluence than in the Dresden protocol.
Authors: Evan K Dackowski; Juan Batlle Logroño; Cristina Rivera; Najwa Taylor; Patrick D Lopath; Roy S Chuck Journal: Transl Vis Sci Technol Date: 2021-04-29 Impact factor: 3.283