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The garter snake provides a unique model for in-vivo imaging of photoreceptor damage induced by laser retinal exposure. Laser thermal/mechanical retinal injury induced alterations in photoreceptor structure and leukocyte cellular behavior. Photoreceptors turned white, lost mode structure, and swelled; leukocyte activity was observed in the vicinity of photoreceptor cells. Non-thermal alterations were identified with a bio-tag for oxidative stress. Mechanisms of photoreceptor recovery and replacement were observed and evaluated for active cytoskeletal systems by using an anti-actin tag that could detect the presence of active cytoskeletal systems resident in photoreceptors as well as other retinal systems.

Purpose: To evaluate choroidal perfusion following creation of a laser-induced macular hole in a nonhuman primate model., Methods: Six rhesus monkeys underwent macular exposures delivered by a Q-switched Nd:YAG laser. The lesions were evaluated with fluorescein angiography and indocyanine green angiography using scanning laser ophthalmoscopy., Results: Each lesion produced vitreous hemorrhage and progressed to a full-thickness macular hole. Indocyanine green angiography revealed no perfusion of the choriocapillaris beneath the lesion centers. Fluorescein angiography demonstrated mild enlargement of the foveal avascular zone due to loss of perifoveal capillaries. Histopathologic evaluation showed replacement of the choriocapillaris with fibroblasts and connective tissue., Conclusions: Nd:YAG laser-induced macular holes result in long-term impairment of choroidal perfusion at the base of the hole due to choroidal scarring and obliteration of the choriocapillaris. Evaluation of choroidal perfusion may be useful in assessment of laser-injured patients. Impairment in choroidal perfusion may have functional implications for surviving photoreceptors.

During long-term viewing of a continuous light source, head and eye movements affect the distribution of energy deposited in the retina. Previous studies of eye movements during a fixation task provided data used for revising the safety limits for long-term viewing of such sources. These studies have been continued to determine the effect of source brightness on the nature of fixational eye movements. Volunteers fixated for 50 s on a HeNe laser (lambda = 632.8 nm) masked by a small aperture to produce a target subtending approximately 0.03 mrad in the visual field. The source was attenuated to yield corneal irradiance values in the range 0.6 pW cm(-2) to 6 microW cm(-2). Eye movements were recorded using a Dual Purkinje Image Eyetracker. The data were characterized by fixation ellipses that represent areas of the retina in which the image of the spot was located 68% of the time of each trial. Significant variation across subjects in the tightness of fixation was observed. Over the eight orders of magnitude of source brightness used in this experiment (10(-13) to 10(-6) W cm(-2)), no subject showed more than roughly a factor of two variation in the area of the fixation ellipse. No statistically significant trend in tightness of fixation as a function of source brightness was observed. There was no loss of ability to fixate, nor any drive to aversion, at the higher source intensities.

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.

Changes in rhesus spectral sensitivity were induced at low-level (2.1 log td) repetitive exposure to a visible (514 nm) coherent source. Irradiation involved the entire retina. Long-term suppression of intermediate cones was evident in spectral sensitivity functions measured for a very fine photopic (1.85 min-1) acuity criterion. At slightly coarser acuity criteria (1.42 min-1) but still photopic, evidence of rod intrusion was obtained. Recovery from these effects was not obtainable 14 months post-exposure. Possible morphological correlates at photoreceptor ultrastructural levels are discussed. Optical coherency is implicated in these effects.