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B. Bogner, B. Tockner, C. Runge, G. Grabner, J. W. Kiel, H. A. Reitsamer; Dorzolamide and Brimonidine: Two Oppositional Mechanisms of Reducing Aqueous Humour Formation in Acute Rabbit Experiments. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3931.
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To investigate the effect of topical dorzolamide on ciliaryblood flow (CilBF) and aqueous flow (AqF) in relation to theeffect of brimonidine on the two variables.
In anesthetized rabbits mean arterial pressure (MAP), intraocularpressure (IOP) and orbital venous pressure (OVP) were measuredby direct cannulation of the central ear artery, the vitreous,and the orbital venous sinus, respectively. Laser Doppler flowmetrywas used to record CilBF continuously. Aqueous flow (AqF) wasmeasured simultaneously by flourophotometry. After baselinemeasurements either dorzolamide or brimonidine was applied topically.
The effect of dorzolamideon CilBF is caused by a significant reduction of ciliary bodyvascular resistance (CilR) while the effect of brimonidine iscaused by a significant increase in CilR. Topical dorzolamidehad no significant effect on MAP and heart rate, brimonidinealso had no effect on MAP but decreased heart rate significantly
We conclude that dorzolamide increases CilBF by reducing vascularresistance, an effect that is independent of the decrease inIOP. The reduction in AqF is primarily caused by dorzolaminde’sdirect inhibition of aqueous secretion and is not due to ciliaryvasoconstriction. However, on the other hand, vasoconstrictionseems to be the predominant mechanism by which brimonidine lowersaqueous production in the acute anesthetized rabbit preparation(see figure).
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