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The International Commission on Non-Ionizing Radiation Protection (ICNIRP) established eye-safe exposure limits for laser light based on estimates of the 50% exposure dose (ED50) for retinal damage in animals. The ED50 has not been determined for continuous-wave near-infrared (NIR) light, as may be used in instruments for spectroscopic analysis of the eye. The purpose of this study is to determine the ED50 of 785-nm light delivered by a Raman spectroscopy instrument on the retinas of pigmented rabbits, and to compare that ED50 to the ICNIRP estimates. Light of varying power was focused into the anterior chambers of rabbits for 4, 20, or 300 s. Estimates of spot size on the retina were determined by modifying the schematic rabbit eye with actual axial length and refractive error measurements. Masked examiners determined retinal burns from fundus photographs and fluorescein angiograms made immediately after exposure and again 48-72 h later. Thirty-five of 86 exposed eyes had retinal burns. In 12 of these the burn was not visible until 48-72 h. In 6 the burn was visible on color photographs, but not on fluorescein angiography. The ED50 retinal power density from probit analysis was 14,513 mW cm(-2), 10,369 mW cm(-2), and 5,237 mW cm(-2) for 4-s, 20-s, and 300-s exposures, respectively. Thus, the ED50 for retinal burns from 785-nm light is approximately 7 and 7.5 times the ICNIRP permitted limits for 4- and 20-s exposures, and 5.6 times the limit for 300-s exposures. This is consistent with the ICNIRP intention to set power limits several times less than ED50.

With the easy attainability of hand-held laser devices and the burgeoning light emitting diode (LED) technology, safety standards for long-term viewing of continuous light sources are being scrutinized. One concern is with quantifying the effect of head and eye movements on the distribution of energy over the retina. This experiment describes target motion over the retina as a result of head and eye movements during a deliberate fixation task. Volunteers deliberately fixated, with (fettered) and without (unfettered) head and chin rest support, on LEDs that subtended a 0.1 min of arc visual angle. A Dual Purkinje Image Eyetracker measured eye position during each 100-s fixation trial. The data showed an elliptical retinal energy distribution, oriented on the temporal/ nasal retinal axis, with a major axis 1.5 times greater than the minor. The average half-maximum diameter for the major axis was 40 microm for the fettered and 107 microm for the unfettered condition. The retinal area illuminated from head and eye movements showed a positive linear relationship with time. Peak retinal radiant exposure at 100 s was reduced by a factor of 10 as a result of eye movements and by a factor of 30 as a result of head and eye movements. Although the net result was a reduction in radiant exposure from a "no-movement" baseline, the distribution of energy over the retina was well within the 200 microm foveal boundary. The data suggest that the laser permissible exposure limits for long term viewing of a small continuous wave source include a factor that adjusts for this reduction in retinal radiant exposure with time.

The application of occupational limits (ELs) in the outdoor laser environment requires an understanding of the radiometric methods required to evaluate field exposures with respect to the ELs. The limiting aperture required to adequately specify the EL must always be kept in mind. Since all exposure limits are defined as a function of time, electro-optical detectors and instrumentation must have an adequate temporal response and have an absence of saturation effects. As a field-expedient method thermally sensitive paper can also be employed to estimate the output radiant exposure of pulsed lasers. For evaluating potential ocular hazards in the retinal hazard spectral region (400 to 1400 nm), one should employ a 7-mm aperture. For evaluating potential hazards to the skin and the cornea, a 1-mm limiting aperture is justified. Although the impact of the 1-mm limiting aperture is to reduce the limiting power which is considered safe--the accessible emission limit for Class 1 laser products, it nevertheless is justified for field exposure of the eye, as has been shown in recent experimental studies of corneal injury.