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R.J. Truscott, S. Vazquez, N. Parker, M. Davies; If You Are Over 50, is it Safe to Go Out in the Sun ? . Invest. Ophthalmol. Vis. Sci. 2003;44(13):306.
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Purpose: Primates have evolved an efficient mechanism to protect the lens and retina from UV damage, and at the same time, to aid in visual acuity. This is the UV filter pathway, which is located in the lens and is based on the production of kynurenine metabolites that absorb light in the 300-400nm band. We are investigating the effects of age on this system. Methods: The content of free UV filters in human lenses of various ages was measured by HPLC. Protein-bound UV filters were quantified after hydrolysis of the proteins Results: Marked changes in the lens UV filter system occur with age. These have important consequences. In young lenses, UV absorption is accomplished by free UV filters. The concentration of these free UV filters decreases linearly with age. Kynurenine, 3-hydroxykynurenine and 3-hydroxykynurenine glucoside each decrease at 12% per decade. If this were the only change, then the human eye would be significantly more susceptible to UV-induced damage as we get older. After middle age, however, the concentration of protein-bound UV filters increases. It had been thought that this may partly compensate for the loss of free UV filters, but unfortunately new data indicates that the properties of free and bound UV filters are different.While free UV filters absorb light and do not act as photosensitisers, irradiation of UV filters that are bound to proteins results in the production of protein peroxides. Since oxidation is the hallmark of age-related nuclear cataract, this finding suggests that the progressive accumulation of UV filters on the proteins in the center of the lens that takes place after middle age, may in fact facilitate the oxidation of these proteins on exposure of the eye to UV light. Conclusion: Since the levels of free UV filters are decreased, while protein-bound UV filters are increased, relative to young lenses, exposure to light after middle age may predispose lens proteins to oxidation and therefore to nuclear cataract.
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