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Patients whose eyes require enucleation for medical reasons were exposed to focused argon laser beams in a regular pattern of locations in the eye, especially in the macula, including the fovea. The power levels were suprathreshold to just produce instantaneous lesions. The ophthalmoscopic appearance of the resultant lesions was correlated with loss of function and with subsequent histological examination. An argon laser lesion in the macula may have greater functional impairment than a comparable ruby laser lesion. In lesions outside the macula the damage is confined to the retinal pigment epithelium and adjacent structures. In markedly suprathreshold lesions the outer segments of the rods were less disturbed than the inner nuclear and plexiform layers. Within the macula there are usually two damage locations separated by unchanged layers of the retina. In the pigment epithelium in which the damage was the same or less than in lesions outside the macula, there was a larger area of damage in the outer plexiform layer. Foveal lesions had greater damage to the fiber layer of Henle (outer plexiform layer) than in adjacent areas of the macula at comparable power levels.

Patients whose eyes require enucleation for medical reasons have been exposed to focused laser beams in a regular pattern of locations in the eye, including the macula in both the parafoveal and foveal regions. A variety of power levels have been used from ruby, continuous wave helium-neon, and continuous wave argon lasers. The ophthalmoscopic appearance of the resulting lesions has been correlated with any loss of function and with the subsequent histological examination. Other diagnostic tests such as fluorescein angiography have been used. The following effects of laser exposures in the macula were consistently seen: Minimum lesions outside the fovea could not be detected functionally; Suprathreshold lesions large enough to be useful as marker lesions parafoveal produced small scotomas; Exposure to approximately 1/3 (50%) level for macular burns did not produce a visible lesion of the fovea, nor did it appear to have any effect on function; Exposures which do not produce an alteration to the fovea visible by fundoscopy do not alter function; Minimum visual lesions in the fovea may degrade vision to approximately 20/40. (Author Modified Abstract)

In studies of retinal damage by the Q-switched ruby laser, threshold values were determined for both 'minimal' and large retinal spot sizes. In addition to using the conventional ophthalmoscopic methods for detecting injury in the living animal, histopathological examinations were performed on a number of irradiated eyes following enucleation. The microscopic evaluation of irradiated tissue was considered to be particularly important in the minimal retinal spot size experiments in order to support the ophthalmoscopic observations of very small retinal lesions. In analyzing the data the macular and extramacular exposure sites have been considered separately because of conflicting reports concerning the relative sensitivity f these two retinal areas to laser damage. (Author), Joint AMRDC-AMC Laser Safety Team.