The eye
As with effects on the skin, the various incoming sun rays penetrate the eye to different depths. While UVB is fully absorbed by the cornea, UVA passes through these surface layers to the lens. Among adults only 1 per cent or less of incoming UV radiation reaches the retina because of the filter function of cornea and lens. In contrast visible light easily penetrates through to the retina, where it activates photoreceptors and starts the chain reaction of biochemical processes to produce a visible image.