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The effects of repeated exposures to UV-A (335 nm) and UV-B (305 nm) radiation on the crystalline lens were studied by treating cultured bovine lenses daily or weekly. The effects of irradiation on lens optical quality were monitored using an automated scanning laser system that records both relative transmittance and focal length across the lens. Relatively low radiant exposures of UV-B were used (0.06, 0.03, 0.01 J/cm2) compared to UV-A (1.44 J/cm2). In total, 38 treated lenses and 32 controls were cultured for times ranging from 400-1000 hours. Results indicate that this range of UV-B exposure may represent the threshold for in vitro UV-B induced opacification. Lenses treated weekly with 0.06 J/cm2 UV-B showed a significant decrease in transmittance compared to controls 69 hours after the first treatment and an increase in focal length variability. The ability of the lens to repair itself, as found in a previous single dose study, was absent after repeated doses. Lenses exposed daily to 0.03 and 0.01 J/cm2 UV-B showed no significant change in transmittance or focal length variability compared to controls. Daily exposure to 1.44 J/cm2 UV-A resulted in no significant change in transmittance or focal length variability compared to controls.

The effect of UV-B radiation on the crystalline lens was examined by subjecting bovine lenses in culture to varying low exposures at 300 nm. Lens optical quality was monitored on a long-term basis (to 1000 hrs.) with an automated scanning laser system that recorded both change in relative scatter and focal length across each lens. Data were collected for 20 lens positions at each scan. Radiant exposure levels consisted of 0.5, 0.25, 0.125, 0.06 and 0.03 Jcm-2. Twenty irradiated lenses were compared to twelve untreated controls. All of the irradiated lenses showed changes in scatter and focal length relative to the controls. Most (about 75%) of the treated lenses showed significant increases in scatter (200-400%) and focal length (10-20%) at 40 to 60 hours after exposure. A similar time frame for lens damage was noted by visual inspection. Exposure to UV-B at the above doses did not affect culture longevity.