Additivity and repair of actinic retinal lesions.

Extensive exposures to light of intensities insufficient to produce thermal damage can still result in retinal damage via nonthermal mechanisms. In this work, the additivity and the repair rate for this actinic damage were measured. Rhesus monkey retinas were exposed to 458 nm light from an argon-ion laser at a dose equivalent to half the threshold retinal irradiance. After prescribed time intervals, the retinal sites were re-exposed to determine the split-dose threshold. This threshold is related to the single-dose threshold through the additivity, which in turn is dependent on the time between exposures. The observed recovery of tissue could be fitted by a single exponential with a time constant of 4 days. This result is incorporated in an analytic expression for the cumulative effect of repeated doses.