Additive effects of ultraviolet radiation.

A 5000 W xenon-mercury high pressure lamp and a double monochromator were used to produce a 3.3-nm half-bandpass ultraviolet (UV) radiation at 295 nm. Pigmented rabbit eyes were irradiated with radiant exposures given in joules per cm2 and ranging from 0.014 to 1.0 J.cm-2 and evaluated by slitlamp biomicroscopy. Corneal threshold (Hc) was 0.05 J.cm-2 and lens threshold (hL) was 0.75 J.cm-2. Other eyes were irradiated with 2 Hc and evaluated from 4 to 24 hr at 4-hr intervals. After a latent period of 4 hr, the corneal response was observed to increase to a maximum by 12 hr. Addition eyes were subjected to repeated Hc and 0.5 Hc followed by Hc exposures with varying intervals between exposures. Corneal damage was only greater than that expected from a single Hc exposure if the separation between the two Hc exposures did not exceed 8 hr. The subthreshold exposures did not sensitize the cornea to later Hc irradiations. The most repeatable and reliable corneal response to these levels of UV was the development of corneal epithelial granules.