Ultraviolet radiation and cataract.

While solar radiation falling on earth comprises light in the infrared, visible, UVA, UVB, and even UVC ranges, the light incident on, and thus important to the biology of, the eye lens is essentially in the visible and UVA regions. Thus, direct photochemical damage to the lens from UVB radiation is minor, though long-term UVA (and even visible range) irradiation is seen to lead to lens malfunction. Short-term exposure of the lens in vivo to UVA light leads to compromised optical and biochemical properties which are repaired in time, while higher doses affect permanent damage. Such longer wavelength light-mediated changes in the lens occur through photodynamic means, affected by some of the compounds that accumulate in the lens over a period of time, which act as sensitizers. Isolation and chemical identification of over a dozen such compounds has been done, and their photoactive properties have been studied. While several of these are photodynamic and generate reactive oxygen species when UVA light is shone on them, other compounds that accumulate in the lens act as antioxidants.