We describe a new model for laser-induced retinal damage. Our treatment is prompted by the failure of the traditional approach to accurately describe the image size dependence of laser-induced retinal injuries and by a recently reported study which demonstrated that laser injuries to the retina might not appear for up to 48 h post exposure. We propose that at threshold a short-duration, laser-induced, temperature rise melts the membrane of the melanosomes found in the pigmented retinal epithelial cells. This results in the generation of free radicals which initiate a slow chain reaction. If more than a critical number of radicals are generated then cell death may occur at a time much later than the return of the retina to body temperature. We show that the equations consequent upon this mechanism result in a good fit to the recent image size data although more detailed experimental data for rate constants of elementary reactions is still required. This paper contributes to the current understanding of damage mechanisms in the retina and may facilitate the development of new treatments to mitigate laser injuries to the eye. The work will also help minimize the need for further animal experimentation to set laser eye safety standards.

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In this report we examine how the fluid host influences the nonlinear optical response of carbon black suspensions on both the nanosecond and microsecond timescales. It is shown that there is a strong fluid dependence on the microsecond timescale and a smaller but still significant dependence on the nanosecond timescale. The temporal dynamics are studied and it is proposed that bubble formation is responsible for the enhanced microsecond response observed in the more volatile fluids. A beam propagation scheme is introduced and it is demonstrated that by making simple assumptions about the microscopic nonlinear loss mechanism the experimental data can be simulated.

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For the dark-adapted human eye the diffraction limited retinal image is approximately 2.8 microm in diameter for green light, although the estimation of the size of the retinal image resulting from the incidence of a collimated beam on the cornea is problematical and has been estimated to be anywhere from 10 to 30 microm. The resolution of this difference is important for the accurate determination of the retinal hazards of optical sources and for setting safety limits for laser-retinal exposure. Using literature results for the aberrations measured in a population of healthy young adults, beam propagation calculations of retinal images are presented for different pupil diameters. Using the concept of a generalized Strehl ratio, retinal damage thresholds, EDx, are derived for exposures in the thermal confinement regime (exposure times approximately less than 10 micros). The most vulnerable eyes are predicted to be those with pupil sizes 2-3 mm such as would be found under daylight illumination. The results also suggest that populations with particularly small ocular aberrations and correspondingly high visual acuity may be significantly more vulnerable than a "normal" population.