Ocular phototoxicity and psoralen plus ultraviolet radiation (320-400 nm) therapy: an experimental and clinical evaluation.
The increase in fluorescent chromophores within the human ocular lens is age related, leading to an increasingly yellow core (nucleus) that presumably results from UV radiation exposure. In approximately 10% of our population this process progresses more rapidly, resulting in the formation of the brown (nuclear) cataract. Some lenticular discoloration may be beneficial, since it enables the mature lens to filter UV and short-wavelength visible radiation, thus protecting the retina from potential photodamage. Aphakic primate retinas can be irreversibly damaged by exposure to approximately 5 mW.cm-2 long-wavelength UV (greater than 325 nm) radiation. Photosensitized damage to the lens and retina with psoralen plus UV radiation (320-400 nm) (PUVA) has been demonstrated in experimental animals, and cataracts have recently been reported in patients given PUVA therapy. A new method to screen patients for lens damage is by enhanced fluorescence measurements. This method, UV slit-lamp densitography, permits detection of lenticular photodamage at a molecular level, years before visible opacities become manifest by conventional slit-lamp examination. This procedure has also demonstrated a significantly lower level of lens fluorescence (hence decreased filtering capacity) in patients with retinal degenerative diseases, suggesting UV photodamage as a factor in the progression and perhaps pathogenesis of these conditions.