Veiling glare: the visual consequences of near-UV/blue light induced fluorescence in the human lens

Abstract

Irradiation of the ocular lens of numerous species by near-UV or short-visible wavelengths induces a blue-green fluorescence, which can be a source of intraocular veiling glare. Wavelengths longer than the ~365-nm lens absorption peak induce progressively weaker but also progressively more red-shifted fluorescence emission. The more red-shifted emission has a higher luminous efficiency and, in fact, earlier studies in this laboratory have demonstrated that the lens fluorescence in the non-human primate yields an approximately constant luminous efficiency when excited by equal radiant exposures over the wavelength range from 350 to 430 nm. Now, with the recent development and projected widespread use of blue and near-UV diode lasers, a further study extending the measurements of the induced fluorescence efficiency and of the consequent veiling glare to the human lens seemed timely. The current study quantifies the fluorescence intensity induced in the human lens, both in terms of radiance and luminance, as a function of exciting light intensity, excitation wavelength and subject age. The spatial distribution of the emitted fluorescence is also examined. These data are shown to imply that exposure to near-UV/blue wavelength sources at safe exposure levels (reference existing laser safety standards) can induce a veiling glare intense enough to degrade visual performance, and that the fluorescence intensity and consequent glare disruption show little dependence on subject age.