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 approximately 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 nonhuman 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" 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 (according to 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.

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SIGNIFICANCE Optical distortion is the image degradation of a visual target induced by a transparent material. Current Air Force evaluation of distortion is an entirely qualitative assessment of the acceptability of image distortion. The novel, quantitative technique described here is capable of identifying 0.1% distortion across an array of optical samples. PURPOSE Optical distortion is the effect by which a transparent object spatially warps the perception of a visual target. All U.S. Air Force visors are required to pass military standards outlined in MIL-DTL-43511D (2006). Although specifications for the optical distortion setup and critical areas of vision are outlined, the evaluation technique is entirely qualitative, with a panel of several human evaluators assessing the distortion acceptability. The evaluation is not explicitly tied to a visual acceptability rating and has variable levels of consistency over time or across evaluators and a fabrication tolerance limit of 3% distortion. METHODS The technique proposed in this article is a modification to the recommended optical tester used to analyze distortion patterns. An image-processing algorithm was developed to analyze patterns of Ronchi grid distortion mathematically to provide a quantitative approach that can subsequently be tied to visual metrics. RESULTS This effort developed and refined an algorithm that allowed for a standardized assessment creation of high-resolution distortion maps from digital images. A 1-inch-diameter region imaged through ophthalmic material allowed for two-dimensional median filtering down to 15-pixel areas with enhanced contrast between grid lines leading to possible resolution capabilities of 0.10% distortion. CONCLUSIONS Quantification of the standard for measuring optical distortion is the initial step toward determining the effects of distortions on human visual performance metrics. The future goal for this effort will focus on obtaining empirical results from human experimental efforts and relating the distortion location and magnitude to effects on visual performance activities.

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