Joshua N Webb1, Johnny P Su1, Giuliano Scarcelli2. 1. From the Fischell Department of Bioengineering, University of Maryland, College Park, Maryland, USA. 2. From the Fischell Department of Bioengineering, University of Maryland, College Park, Maryland, USA. Electronic address: scarc@umd.edu.
Abstract
PURPOSE: To quantify corneal mechanical changes induced by corneal crosslinking (CXL) procedures of different ultraviolet-A (UVA) intensity and exposure time using Brillouin microscopy. SETTINGS: University of Maryland, College Park, Maryland, USA. DESIGN: Experimental study. METHODS: Porcine cornea samples were debrided of epithelia and soaked with riboflavin 0.1% solution. Samples were exposed to a standard 5.4 J/cm2 of UVA radiation with varying intensity and exposure time as follows: 3 mW/cm2 for 30.0 minutes, 9 mW/cm2 for 10.0 minutes, 34 mW/cm2 for 2.65 minutes, and 50 mW/cm2 for 1.80 minutes. Using Brillouin microscopy, the Brillouin modulus for each sample was computed as a function of radiation intensity/exposure time. For validation, the Young's modulus was found with the stress-strain test and compared at each irradiation condition. RESULTS: The standard 3 mW/cm2 irradiance condition produced a significantly larger increase in corneal Brillouin modulus than the 9 mW/cm2 (P ≤ .05), 34 mW/cm2 (P ≤ .01), and 50 mW/cm2 (P ≤ .01) conditions. Depth analysis showed similar anterior sections of the standard and 9 mW/cm2 conditions but significantly less stiffening in the central and posterior of the 9 mW/cm2 condition. The stiffening of the standard protocol was significantly larger in all sections of the 34 mW/cm2 and 50 mW/cm2 conditions (P ≤ .01). The overall change in Brillouin-derived Brillouin modulus correlated with the increase in Young's modulus (R2 = 0.98). CONCLUSIONS: At a constant UVA light dose, accelerating the irradiation process decreased CXL stiffening. Brillouin analysis showed that accelerated protocols were especially ineffective in the deeper portions of the cornea.
PURPOSE: To quantify corneal mechanical changes induced by corneal crosslinking (CXL) procedures of different ultraviolet-A (UVA) intensity and exposure time using Brillouin microscopy. SETTINGS: University of Maryland, College Park, Maryland, USA. DESIGN: Experimental study. METHODS: Porcine cornea samples were debrided of epithelia and soaked with riboflavin 0.1% solution. Samples were exposed to a standard 5.4 J/cm2 of UVA radiation with varying intensity and exposure time as follows: 3 mW/cm2 for 30.0 minutes, 9 mW/cm2 for 10.0 minutes, 34 mW/cm2 for 2.65 minutes, and 50 mW/cm2 for 1.80 minutes. Using Brillouin microscopy, the Brillouin modulus for each sample was computed as a function of radiation intensity/exposure time. For validation, the Young's modulus was found with the stress-strain test and compared at each irradiation condition. RESULTS: The standard 3 mW/cm2 irradiance condition produced a significantly larger increase in corneal Brillouin modulus than the 9 mW/cm2 (P ≤ .05), 34 mW/cm2 (P ≤ .01), and 50 mW/cm2 (P ≤ .01) conditions. Depth analysis showed similar anterior sections of the standard and 9 mW/cm2 conditions but significantly less stiffening in the central and posterior of the 9 mW/cm2 condition. The stiffening of the standard protocol was significantly larger in all sections of the 34 mW/cm2 and 50 mW/cm2 conditions (P ≤ .01). The overall change in Brillouin-derived Brillouin modulus correlated with the increase in Young's modulus (R2 = 0.98). CONCLUSIONS: At a constant UVA light dose, accelerating the irradiation process decreased CXL stiffening. Brillouin analysis showed that accelerated protocols were especially ineffective in the deeper portions of the cornea.
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