The use of intraocular lenses (IOLs) to replace cataractous lenses has raised question of possible retinal damage due to exposure to ultraviolet (UV) radiation. Three groups of cynomolgus monkeys underwent cataract operations and either received normal UV-transparent IOLS or UV-opaque IOLs, or were left aphakic. All eyes were later exposed to UV light for varying periods of time. Exposure to UV light produced severe retinal lesions. In aphakic eyes and those with normal IOLs lengthy exposure to low levels of UV light produced lesions similar to those seen after brief, very intense UV radiation. Eyes with UV-opaque IOLs displayed no such lesions. Our results indicate that clinicians should consider the use of UV-opaque IOLs.