The cornea absorbs wavelengths below 300 nm, the lens absorbs wavelengths between 300 and 400 nm,and wavelengths greater than 400 nm are transmitted to the retina. The lens absorb almost all UVR to which it is exposed, and any resulting unstable free radicals cause molecular changes. The first active tissue of the lens that encounters UVR is the lens epithelium, which is susceptible to damage apparent in the epithelial layer may lead to irreversible changes throughout the lens, although the machanism by which this progresses has not been defined.
UVR absorbs by lens fiber causes oxidative damage, leading to degradation and modification of lens proteins. An association exists between ocular exposure and increased risk of lens opacity. UVR absorption also increases chromophore concentration; yellow pigments accumulate in the center of the lens. The yellowing may progress to a dark-brown hue, which is called lens brunescence.