Effects of Lasers on the Human Eye

In dealing with the relationship between human vision and lasers, this largely theoretical paper places particular emphasis upon the use of lasers within the normal operating range of the visual system, and upon the mechanisms by which laser radiation can cause threshold damage to the eye. Parallel but subordinate sections present some fundamentals of laser radiation, of the relevant aspects of the visual system, and of unit systems for the specification of laser output. A new approach to understanding laser radiation damage to the eye is developed by means of a model limited to conditions existing only at the threshold of damage. It is shown that such threshold damage to the visual system is primarily due to the effects of heat alone, but that photochemical effects and acoustic shockwaves can potentially be a cause of the threshold damage that cannot be entirely rejected under all conditions. A theoretical estimate of retinal irradiance for threshold damage is made and shown to be consistent with empirical findings. A survey of empirically determined damage thresholds is presented. A valid method of computing retinal irradiance from a laser is given, and the direction and magnitude of errors in earlier formulations are pointed out.