Mechanical outcome of accelerated corneal crosslinking evaluated by Brillouin microscopy

Abstract

To quantify corneal mechanical changes induced by corneal crosslinking (CXL) procedures of different ultraviolet-A (UVA) intensity and exposure time using Brillouin microscopy. University of Maryland, College Park, Maryland, USA. Experimental study. Porcine cornea samples were debrided of epithelia and soaked with riboflavin 0.1% solution. Samples were exposed to a standard 5.4J/cm2 of UVA radiation with varying intensity and exposure time as follows: 3mW/cm2 for 30.0minutes, 9mW/cm2 for 10.0minutes, 34mW/cm2 for 2.65minutes, and 50mW/cm2 for 1.80minutes. 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. The standard 3mW/cm2 irradiance condition produced a significantly larger increase in corneal Brillouin modulus than the 9mW/cm2 (P≤.05), 34mW/cm2 (P≤.01), and 50mW/cm2 (P≤.01) conditions. Depth analysis showed similar anterior sectionsof the standard and 9mW/cm2 conditions but significantly less stiffening in the central and posterior of the 9mW/cm2 condition. The stiffening of the standard protocol was significantly largerin all sections of the 34mW/cm2 and 50mW/cm2 conditions (P≤.01). The overall change in Brillouin-derived Brillouin modulus correlated with the increase in Young's modulus (R2=0.98). At a constant UVA light dose, accelerating the irradiationprocess decreased CXL stiffening. Brillouin analysis showed that accelerated protocols were especially ineffective in the deeper portions of the cornea.