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  • Title: Resistance to blood flow in the rabbit ophthalmic artery after topical treatment with timolol.
    Author: Liu JH, Li R, Nelson TR, Weinreb RN.
    Journal: J Ocul Pharmacol Ther; 2007 Apr; 23(2):103-9. PubMed ID: 17444797.
    Abstract:
    PURPOSE: The aim of this study was to investigate the resistance to blood flow in the ophthalmic artery of rabbits receiving topical treatment with timolol. METHODS: Eight (8) New Zealand albino rabbits received 20 mul of timolol treatment (vehicle, 0.1%, 0.33%, 1%, and 3.3%) on the right eye. Blood-flow velocity in the ophthalmic artery was determined in the treated eye using color Doppler imaging (CDI) with a 12-MHz linear ultrasound transducer prior to the treatment and at 0.5, 1, 1.5, 2, and 3 h after the treatment. Intraocular pressure (IOP) was measured in both eyes, using a pneumatonometer at the same time points. Pourcelot's resistive index of blood flow was calculated, using the peak systolic velocity and the end diastolic velocity. A control experiment was performed with CDI obtained from the right eye when the left eye was treated with 1% timolol. RESULTS: In the eye treated with 1% and 3.3% timolol, a dose-dependent increase in the resistive index of blood flow occurred in the ophthalmic artery. No change in the resistive index occurred when the contralateral eye was treated with 1% timolol. Changes of IOP were not different between the two eyes under all the experimental conditions. Timolol, at all concentrations, caused a significant reduction of heart rate. A similar reduction of heart rate occurred when either eye was treated with 1% timolol. CONCLUSIONS: Topical treatment with timolol in rabbits can increase the resistance to blood flow in the ophthalmic artery. This effect is caused by a mechanism local to the eye and is not dependent on an IOP change.
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