Morphological Changes in the Ciliary Epithelium of Pigmented Rabbits by Intravitreal Injection of Apraclonidine

Rho, Sae Heun; Yoo, Ki Su

Abstract

The effects of clonidine that is an alpha2-adrenergic agonist are complex in that the intraocular responses are biphasic and dose dependent. The mechanisms of the ocular hypotensive responses to clonidine in the treated and the contralateral untreated eyes seemed to be dependent on the central activity of clonidine and the intact peripheral adrenergic system. Apraclonidine is a clonidine derivative which penetrates into the blood-brain barrier minimally and lowers the intraocular pressure significantly not accompanied by systemic side effects such as change in blood pressure and pulse rate. The main purpose of the present study is to use apraclonidine to elucidate the influence of the central and peripheral sympathetic activity in the change of the morphology of the ciliary nonpigmented epithelium in the pigmented rabbits 0.1 cc of 1% apraclonidine was injected into the vitreous cavity of pigmented rabbits after removal of 0.1 cc of aqueous humor from the anterior chamber and the eyes were enucleated on 1, 3, 5, 7 days after injection. The eyes were observed with light microscopic examination. 1. In the 1st day's specimen, swollen nonpigmented epithelium and increased pigments were noted in the treated eye. 2. In the treated eye on the 5th day, vacuole like appearances under the nucleus of the nonpigmented epithelium were noted. 3. Except for the appearance of slightly increased pigmented granules in the 3rd and 5th day's specimen, there were no significant changes in any of the nontreated eyes. 4. The mechanism of the hypotensive response of apraclonidine seemed to be dependent on the alpha2-adrenergic receptors which are located in the eye, not on the central nor on the peripheral adrenergic system.