The effect of autonomic receptor blockers on the ocular response to topical chemical irritation.

Abstract

Topical chemical irritants induce an acute reaction in the eye, consisting of an increased intraocular pressure (IOP), breakdown of the blood-aqueous barrier, anterior uveal vasodilation and miosis. In the present study these effects were studied in the rabbit eye after topical application of neutral formaldehyde by measuring IOP continuously using electromanometrical equipment. The protein content of the aqueous humour was measured and miosis as well as anterior hyperemia were analyzed. Intravenously injected sodium fluorescein was used to visualize the site of the disruption of the blood-aqueous barrier in freeze-dried specimens. Iridectomies were performed to study the mechanisms of hypertension and disruption of the blood-aqueous barrier. In iridectomized rabbits the acute irritative response was very similar to that of normal eyes. Breakdown of the blood-aqueous barrier, miosis and anterior hyperemia occurred. However, the increase in IOP was only partially reduced. This indicates that a pupillary block due to the intense miosis plays a minor role in the hypertensive reaction or in the breakdown of the barrier. The effect of three autonomic receptor blocking agents: phentolamine (alpha-adrenergic antagonist), timolol (beta-adrenergic antagonist) and biperiden (cholinergic antagonist) on the irritative ocular response caused by formaldehyde was studied. Phentolamine proved to be an efficient inhibitor of the hypertensive reaction. It also effectively prevented the breakdown of the blood-aqueous barrier. Biperiden inhibited only slightly the increase in IOP caused by formaldehyde. Timolol had no significant effect. None of these three antagonists was able to prevent the miosis or hyperemia. The present findings indicate that a part of the irritative response is mediated by a phentolamine-sensitive neuronal pathway.(ABSTRACT TRUNCATED AT 250 WORDS)