Characterizing temperature-dependent photo-oxidation to explain the abrupt transition from thermal to non-thermal laser damage mechanisms at 413 nm

Abstract

Laser exposure duration dictates whether tissues subjected to short visible wavelengths ( ≤ 514 nm) are damaged by thermal (e.g. 0.1 s) or non-thermal ( ≥ 100 s) mechanisms. Somewhere between these extremes, an abrupt transition between the two damage mechanisms has been found for both in vitro and animal retinal models (J. Biomed. Opt. 15, 030512, 2010). Non-thermal (photochemical) damage is characterized by an inverse relationship between damage threshold irradiance and exposure duration (irradiance reciprocity). We have found that exposures of 40 - 60 s in an in vitro retinal model require radiant exposures well above the expected requirement for nonthermal damage, introducing the concept that damage was forced to be thermal in mechanism. Here we quantify and compare photo-oxidative processes at ambient temperatures between 35 - 50 °C.