Short-term effect of ß-adrenoreceptor blocking agents on ocular blood flow

Abstract

Purpose. In this study the acute effect of the topically-delivered non-selective ß-blockers timolol and carteolol, and the selective ß-blocker betaxolol, were evaluated with respect to ocular blood flow, intraocular pressure (IOP) and vessel resistance in rabbits’ eyes. Methods. In a double masked randomized design, one eye of each subject (n = 9) received two drops of 0.5 % timolol or 2 % cartelol or 0.5 % betaxolol ophthalmic solution and a separate group of nine rabbits received two drops of placebo consisting of physiological saline in both eyes to serve as control. Using hydrogen clearance method, ciliary body blood flow (CiBF), choroidal blood flow (CBF), and retinal blood flow (RBF) were measured. IOP and systemic mean arterial pressure (MAP) of each subject were measured under same condition before and after the administration of respective drugs to calculate the ocular perfusion pressure (OPP) and vessel resistance. Results. In timolol- and carteolol-treated eyes significant reduction was observed in IOP (p < 0.01), CiBF (p < 0.01), CBF (p < 0.01) and RBF (p < 0.01) compared to control eyes. However, in betaxolol-treated eyes a marginal reduction in IOP was observed accompanied by significant increase in CiBF (p < 0.01) and RBF (p < 0.05). The non-selective ß-blocker-treated eyes tended to have increased vessel resistance, whereas, selective ß-blocker-treated eyes tended to have decreased vessel resistance. Conclusions. Our current results comparing non-selective and selective ß-blockers suggest that the selective ß-blocker betaxolol may be more appropriate for maintenance of retinal blood flow in situations with low perfusion. Currently the mechanism for regulation of IOP is unclear; however, the findings from this study indicate that decreased CiBF may contribute to reduction in IOP.