It has long been recognized that optical radiation may be harmful to the eye; however, the precise exposure conditions, wavelengths and irradiation levels required to injure the cornea, lens and retina have not always been well understood. Ultraviolet (UV) radiation levels that elicit UV photokeratoconjunctivitis are dramatically dependent on wavelength. The damage is the result of a photochemical effect. Lenticular opacities produced in laboratory animals appear to be produced only within a narrow waveband near 300 nm by UV radiation or by extremely high-exposure doses of infrared radiation. Wavelengths between 400 and 1,400 nm may reach the retina in the normal eye, and at sufficient irradiance levels can cause a retinal "burn." Short-wavelength light (blue-violet) can cause a retinal photochemical burn, whereas longer wavelengths and short pulses of light appear to be capable of injuring the retina by a thermal damage mechanism. It has only recently been appreciated that the geometry of the light source and the direction of exposure (e.g., overhead v direct) play important roles in determining the likelihood of ocular injury.