Bioeffects of near-infrared lasers

Retinal damage thresholds (ED50s) were determined in Rhesus monkey eyes for 100 ms exposures to collimated radiation from a tunable Ti:sapphire laser at several wavelengths from 690 to 900 nm. Prior research using 15 ns duration laser pulses showed a strong variability of ED50 with wavelength for retinal exposure in Rhesus monkeys to laser radiation in the near-infrared spectrum. Current studies with the Ti:sapphire laser show similar variability of ED50 with wavelength for 100 ms retinal exposures. Previously measured light transmission and absorption properties of ocular tissues do not provide a complete or obvious explanation for the significant variations of threshold with small changes in wavelength. Similar wavelength dependencies of ED50 for the two exposure durations in the wavelength range of 750–830 nm suggest that linear absorption is a cause of the variability. However, differences in the ED50 curves at other wavelengths show that nonlinear mechanisms also contribute.