The effect upon the retina of exposure to large fields of bright visible light has been evaluated. The thresholds for permanent retinal damage for four hour exposures in rhesus monkeys have been established for white light, and laser lines of 514.5 nm, 488 nm, 457.9 nm, and 590 nm. The damage has been evaluated by ophthalmoscopy, electroretinography and light and electron microscopy. The shortest wavelength light (457.9 nm) is more effective in causing damage, particularly histological damage, which is spread throughout the fundus and throughout the retinal layers. Functional damage shown by the electroretinogram follows a different action spectrum without the increased effect in the blue. There appears to be more than one mechanism for retinal damage in chronic light exposure, and at least one mechanism is not dependent solely upon the visual pigment and the pigment epithelium. Thresholds of permanent damage appear to be within one or two log units of light levels encountered in the normal visual environment. Newer data suggest that this damage is additive. Daily one hour exposures for four days produce damage equivalent to a single four hour exposure at the same retinal irradiance.

Light damages the cultured bovine retinal epithelium at about the same intensities as those effective in the primate retina, in vivo. Also as in vivo, blue light (457.9 nm) is substantially more damaging than longer wavelengths of the visible spectrum. Experiments were performed to test whether this damage by light is mediated by a photodynamic reaction. Primary confluent monolayer cultures of the bovine retinal epithelium were exposed to 435 nm light for 120 minutes, during which time the oxygen content in the gas phase of the exposure chamber was maintained at a predetermined value. Prior to and after light exposure the cultures were aerated by 20% oxygen. The normal growth medium (Eagle's MEM + 10% fetal calf serum) was used during exposure. Light microscopic and EM examination 24 hours after exposure showed that changes indicating cell death were enhanced by a factor of 10 when exposures were conducted in an atmosphere of 95% oxygen instead of 20% oxygen. No damage at intensities up to 50 mw/sq.cm. was observed with a 0% oxygen atmosphere. These effects were the same when a saline, bicarbonate buffered medium was used during exposure. It is concluded that short wavelength light damage to the retinal epithelium is caused by a photodynamic reaction, i.e. a photosensitized aerobic oxidation. This is the first time that the mechanism of blue light damage on a retinal tissue has been established.(ABSTRACT TRUNCATED AT 250 WORDS)

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