In situ measurements of lens fluorescence and its interference with visual function

Irradiation of the primate lens by near-ultraviolet wavelengths results in a blue fluorescence, which can be an intraocular source of veiling glare. This study quantitated the fluorescence intensity as a function of exciting intensity and wavelength. As the exciting wavelength was increased from 360 to 430 nm, the decreasing fluorescence intensity (for equal radiant exposures) was partially offset by a shift in the fluorescence spectrum to wavelengths of greater luminous efficiency so the luminance of the lens fluorescence remained approximately constant. The measured luminance of the lens fluorescence was high enough to imply degradation of visual function as a result of reduced contrast of the retinal image. To obtain an objective measure of visual deficit associated with the fluorescent glare, the visual evoked potential (VEP) elicited by counterphased sine-wave gratings was recorded while the subject eye was continuously exposed to the 413 nm emission from a krypton laser. The VEP amplitude was reduced in the presence of the exciting laser even at levels defined as "safe" (ie, where exposure levels are insufficient to induce an acute ocular lesion). Because the direct glare effect of the exciting radiation was negligible in this experiment, the VEP response loss is attributed to the effect of the lens fluorescent glare.