Lens lactate dehydrogenase inactivation after UV-B irradiation: an in vivo measure of UVR-B penetration.

PURPOSE To elucidate the spatial distribution of inactivation of lactate dehydrogenase (LDH) in ultraviolet-B radiation (UVR-B)-exposed eyes. To determine the in vivo penetration depth of UVR-B in the lens. METHODS LDH activity in cornea and lens was investigated with an enzyme histochemical technique. Thirty rats were exposed in vivo to UVR-B of approximately 300 nm, and the eyes were enucleated and frozen at 0, 2, and 6 hours after exposure. LDH activity in frozen sections was determined quantitatively in the corneal epithelium and four different regions in the lens. UVR-B penetration depth was estimated by using a calculated Lambertian absorption coefficient. RESULTS The LDH activity was decreased in the cornea and the outer anterior lens cortex at all three time points. The average decrease in enzyme activity in the time range was 35% in the cornea and 20% in the outer anterior lens cortex. UVR-B inhibition of LDH was immediate and not dependent on an inflammatory reaction within the eye. Penetration depth, corresponding to 1/e(2) ( approximately 14%) residual UVR-B intensity, was 0.45 mm. CONCLUSIONS UVR-B does not exhibit any significant effect on LDH activity in the major part of the lens, and this is attributed to the shallow penetration (0.45 mm) of UVR-B into the anterior parts of the lens.