Corneal epithelial injury thresholds for exposures to 1.54 μM radiation-dependence on beam diameter

Corneal epithelial injury thresholds have been determined for exposures to 1.54 μm infrared radiation from an Erbium fiber laser. Thresholds were determined for beam diameters from 0.05 to 0.7 cm for exposures having durations from ∼1 to 100 s and for a fixed beam diameter of 0.1 cm for exposures with durations between 0.036 and 0.26 s. Near-threshold damage appeared within 30 min post-exposure. There was no evidence of latent damage from lesser exposures appearing up to 24-48 h post-exposure. The dependence of the threshold radiant exposures on laser beam diameter for exposures >1 s provides strong evidence supporting a critical temperature damage model. However, the shorter exposures are not in accord with a critical temperature damage model. Thresholds for exposures longer than 1 s are greater than 10 times the maximum permissible exposure (MPE) in ANSI Z-136.5-2000; however, the safety factor decreases to less than 10 for exposures less than 0.1 s with a 0.1-cm-diameter beam.