Review of experimental and computer model retinal injury thresholds in the wavelength regime of 1300 nm to 1400 nm

Abstract

Experimental and computer-model retinal injury thresholds in the regime of 1300 nm to 1400 nm indicate a need to revise the wavelength dependence of the laser safety exposure limits (MPEs) of ANSI Z136.1-2014, ICNIRP and IEC 60825-1:2014. The wavelength dependence of the MPE is expressed by the factor CC in ANSI laser safety standard and the ICNIRP laser exposure limit guideline, and C7 in the IEC laser safety standard; all in the same way. Additionally to the retinal thermal limit, there are limitations provided by dual limits, such as to protect the cornea, that indirectly also limit the energy that passes through the pupil. Experimental injury thresholds in the pulsed regime are available by Vincelette et al. (2009) for a wavelength of 1318 nm in the pulsed regime, as well as by Lund et al. (1981) for 1338 nm mixed with 1318 nm emission. For a relaxed eye of the non-human primate, the exposures in these experiments do not represent small sources but are extended sources (extended retinal images). When the retinal image extent is determined for an actual laser source, a respective CE factor (C6 in the IEC standard) is applicable to increase the MPEs. The experimental data show that injury thresholds are very close or are below the MPE when the MPE is calculated for the respective retinal image diameter. Computer model thresholds fit well with the experimental data points. Computer model thresholds are presented in terms of wavelength dependence, pulse duration dependence and retinal image diameter. These can be used to provide input for a discussion to improve the respective MPEs.