IRRITATION OF THE ANTERIOR SEGMENT OF THE EYE BY ULTRAVIOLET-RADIATION - INFLUENCE OF NERVE BLOCKADE AND CALCIUM-ANTAGONISTS

The aim of this investigation was to determine the influence on anteri or segment inflammation elicited by UV radiation, of ocular denervatio n and pharmacological blockade of sensory nerve fibers with capsaicin, tetrodotoxin and calcium antagonists. Both eyes of pigmented rabbits were exposed for 5 min to UV radiation (254 nm); 24 h later, inflammat ory signs were evaluated by biomicroscopy of the corneal epithelium, t he stroma and the endothelium and scored from 0 to 4. Conjunctival vas odilation and miosis were also assessed. Two weeks before UV exposure, a group of rabbits received a retrobulbar injection of ethanol or of 1% capsaicin. Intact, capsaicin-treated and alcohol-denervated animals were treated topically, prior to UV exposure, with tetrodotoxin (0.78 mM) and the calcium antagonists diltiazem (1-28 mM) and nifedipine (1 0 mM). UV radiation produced at 24 h signs of corneal irritation, conj unctival hyperemia, miosis and elevated protein content of the aqueous humor. Retrobulbar injection of 99% alcohol or 1% capsaicin did not d iminish significantly the inflammation of tissues directly exposed to UV radiation, although extension of inflammatory signs to unaffected a reas was prevented. Pre-treatment of normal and denervated eyes with d iltiazem attenuated UV-induced eye irritation signs at concentrations of 10 mM or over. The effect was less pronounced with tetrodotoxin and was not obtained with nifedipine. These findings suggest that the con tribution of a neurogenic mechanism to anterior segment inflammation i nduced by UV exposure is modest. They also show that high concentratio ns of diltiazem, but not of nifedipine, effectively reduced inflammati on of the anterior segment of the eye evoked by UV radiation. This eff ect appears to be largely independent of the blocking action of this d rug on chemical excitation of nociceptive sensory afferents.