Detection of ultraviolet light by humans as a function of age
Fletcher, Laura Michelle
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It has long been thought that the yellow color of the crystalline lens is what prevents us from being able to see light in the ultraviolet; it has been hypothesized that young children, whose lenses have not yet yellowed, may be able to detect these wavelengths. Studies on ex vivo anterior media transmission characteristics which have included the eyes of infants and young children have noted a small transmission “window” in the lens centered at approximately 320 nm. Additionally, aphakics have been shown to be able to respond to ultraviolet light. Therefore, it seems that when this light reaches the retina, we can indeed detect and respond to it. This study is the first to assess detection of ultraviolet light (315 nm) in phakic children and adults. As the S-cones are the most likely to mediate this ability, S-cone sensitivity was also assessed. There was a very clear relationship between the ability to detect the ultraviolet stimulus and the age of the subject. All subjects under the age of 30 could reliably detect the stimulus. Between the ages of 30 and 40, 38 percent of subjects could detect it; for the remainder, detection was essentially nonexistent. Detection ability was not related to S-cone sensitivity, as assessed by threshold for a 405 nm stimulus. It seems definitive that a visually significant amount of ultraviolet radiation does reach the retina of children and young adults, at least under present testing conditions. Further characterization of the true visual range of humans is needed.