Abstract
Abstract: :
Purpose: We have recently demonstrated that in addition to spectral irradiance, age and exposure time are important variables for cataract development after exposure to ultraviolet radiation (UVR). The purpose of the present paper was to develop a strategy for estimation of risk for cataract development, considering age and exposure time. Methods: Experimental data from UVR induced cataract in the Sprague Dawley rat was used. The spectral relative biological efficiency was estimated based on an action spectrum experiment. The relative age dependence of UVR toxicity was estimated based on an experiment in which it was found that the dose required to cause cataract increases with an exponential decline with age. The biologically efficient spectral irradiance at a certain age was calculated as the biologically efficient spectral irradiance multiplied with the relative sensitivity for the age. The relative exposure time dependence of UVR toxicity was estimated based on an experiment in which it was found that the dose required to cause cataract has a minimum for exposure times around 15 min. The biologically efficient spectral irradiance at a certain exposure time was calculated as the biologically efficient spectral irradiance multiplied with the relative sensitivity for the exposure time. For estimation of safe exposure duration (SED), a library reference of spectral irradiance of the sun at the Canary Islands was used. Results: The spectral biological efficiency has a maximum at 300 nm and drops for shorter and longer wavelengths. The biologically efficient spectral irradiance for the Canary Islands reference sun peaked at 305 nm and dropped for longer and shorter wavelengths. The biologically efficient spectral irradiance was on the order of 4.3 times higher for 3 than for 18 week-old rats, corresponding to an SED of 30 and 130 min., respectively, for the Canary Islands reference sun. The biologically efficient spectral irradiance was on the order of 1.4 times higher for exposure times (constant dose) around 15 min. than for shorter and longer exposures, corresponding to an SED of 70 and 100 min, respectively, for the current Canary Islands reference sun. Conclusion: For estimation of risk for cataract development after exposure to UVR, the biologically efficient spectral radiation should be multiplied with a factor for age and a factor for exposure time.
Keywords: 338 cataract • 537 radiation damage: light/UV • 504 oxidation/oxidative or free radical damage