Effect of body temperature on retinal damage by 488 nm light in rat.

Retinal light damage is influenced by the body temperature during exposure, but previous studies do not agree on the magnitude of the effect. A study in rats with broadband green light reported a much larger effect than a study with 380 nm light. The present study set out to clarify whether the spectral composition of the damaging light is responsible for this discrepancy by using 488 nm instead of 380 nm light. Wavelengths in the range of 470-550 nm are known to produce a different damage type than 380 nm. Small patches of retina of anesthetized rats were exposed to 488 nm radiation of an argon ion laser. Body temperature was varied between 30 and 40.5 degrees C. Three days after irradiation, the retina was inspected by funduscopy and prepared for light microscopy. The dose of radiation needed for a just visible change in fundo decreased by 6% per degree increase in body temperature. Damage was mainly found in the retinal pigment epithelium. Temperature had no effect on damage morphology. The temperature effect at 488 nm is much smaller than reported for broadband green light. We conclude that the spectral composition of the damaging light is not responsible for the discrepancy on the magnitude of the temperature effect. Other differences between the studies must be responsible, such as difference in retinal irradiance levels.