Ultrastructural effects of topical beta-adrenergics antagonists and an alpha-adrenergic agonist on the rabbit cornea

In the present study the effects of P-adrenergic antagonist and a-adrenergi c agonist drugs on rabbit corneas were evaluated in vivo by using transmiss ion electron microscopy. Twenty-four New Zealand albino rabbits were divide d into six groups according to the drug applied. The rabbits to which only balanced salt solution (BSS) or BSS and benzalkonium chloride (BAC) were ap plied were taken as the control groups. The other four groups consisted of the rabbits to which Timoptic 0.5%, Betagan 0.5%, Betoptic 0.5% and lopidin e 1% were applied, respectively. All of drugs were instilled topically twic e dal ly for 6 weeks. In the BSS group, a II layers of the cornea were ultr astructurally normal. In the BSS and BAC group slight epithelial and endoth elial changes were found. However, in the other groups, loss of microvilli, increase in glycogen particles, nuclear indentation, widening of the inter cellular spaces and cytoplasmic vacuolization in epithelium were observed. No significant abnormality was found in the basal lamina, stroma and Descem et's membrane. Slight ultrastructural changes were noted in the endothelium such as vacuolization due to dilatation of the endoplasmic reticulum ciste rnae and focal cytoplasmic lytic areas. The results of this study indicate that various ultrastructural changes occur in groups treated with antiglauc omatous drug and that topical treatment with timolol and apraclonidine for 6 weeks is more toxic to the rabbit cornea than levobunolol and betaxolol.