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In this chapter, the photochemical processes that can affect the eye lens as the result of the passage of the incident light required for vision are described, with special emphasis on those that involve sensitizers that are endogenous or that are age dependent. Riboflavin and the kynurenines are two of these endogenous photosensitizers present in the mammalian eye lens. Upon aging, the lens also accumulates brown fluorophores, derived mainly from the Maillard reaction between vitamin C oxidation products and lysine residues of the crystallins, which exhibit photochemical activity as sensitizers in the UVA and visible region. Although the riboflavin concentration in the lens is very low, the occurrence of in vivo riboflavin-mediated photoprocesses has been demonstrated. The present study quantifies the photosensitizing activity of advanced glycation end products (AGEs) at various oxygen pressures and compares this activity to that of lenticular riboflavin (RF), employing ascorbate and tryptophan (Trp) as the targets of the photochemical modifications. The comparison of the real effect of these two sensitizers in the eye lens takes into account (i) the solar irradiance spectrum; (ii) the absorption properties of AGEs and RF at the concentrations found in the eye lens; and (iii) the quantum yields for the AGEs- and RF-sensitized modification of Trp.

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