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G. Weigert, H. Resch, G. Garhofer, A. Luksch, L. Schmetterer; Effects of Topical Clonidine vs. Brimonidine on Choroidal Blood Flow and Intraocular Pressure During Isometric Exercise . Invest. Ophthalmol. Vis. Sci. 2006;47(13):481.
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Clonidine and brimonidine, two alpha 2 agonists, have been shown to reduce intraocular pressure in glaucoma patients. Little is, however, known about the exact role of alpha receptors in the control of ocular blood flow in the posterior pole of the eye. Hence, we set out to investigate the effects of topical clonidine vs. topical brimonidine on choroidal blood flow and intraocular pressure during isometric exercise.
We performed a randomized double masked, controlled two way cross over study. 12 healthy male non–smoking volunteers, aged between 19 and 35 years were included in the study. 2 drops of clonidine or brimonidine were administered in the subjects` study eyes. Continuous measurement using the compact laser Doppler Flowmeter was done during a 6 minutes squatting period to assess choroidal blood flow regulation during an increase in ocular perfusion pressure. Blood pressure was measured in 1 minute intervals during the squatting period and in 10 minute intervals throughout the study period.
IOP decreased from 13±2mm Hg at baseline to 10±2 and 9±2mm Hg in the clonidine group and to 9±2 and 8±2mm Hg in the brimonidine group after 100 and 170 minutes, respectively (p=0.8 between groups). Choroidal blood flow was significantly reduced by both drugs at baseline (p<0.01 each) as well as during isometric exercise (p<0.01 each). The increase in vascular resistance with clonidine and brimonidine during the present experiments was between 30 and 50%.
Alpha 2 agonists may induce changes in choroidal blood flow even after single topical administration. Long–term studies are required to study potential long–term effects of brimonidine and clonidine.
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