Background: The aim of the present study was to evaluate the effect of intravenously administered clonidine on ocular blood flow in healthy volunteers.
Methods: A randomized, double-masked, placebo controlled, two-way cross-over study was performed in 12 healthy young volunteers. Clonidine (0.2μg/kg) or placebo was administered intravenously over 10 minutes. The effects of clonidine were studied at baseline and up to 150 minutes after infusion. Ocular hemodynamics were measured using laser Doppler flowmetry, laser Doppler velocimetry, and a retinal vessel analyzer. Clonidine significantly decreased mean arterial pressure (MAP) and intraocular pressure (IOP).
Results: Calculated ocular perfusion pressure decreased significantly by -8.7±8.7% after infusion of Clonidine (p<0.01 versus placebo). Retinal arterial diameters increased by +4.4±2.7% (p=0.012 versus placebo), whereas no significant change was observed in retinal veins. Red blood cell velocity decreased by -16 ±14% (p<0.01 versus placebo) after infusion of clonidine. Hence, calculated retinal blood flow decreased by -14±12% (p=0.033 versus placebo). Choroidal blood flow increased by +18±19% (p<0.01 versus placebo) and optic nerve head blood flow by +16±23% (p=0.046 versus placebo) 30 minutes after administration of clonidine but both returned to baseline thereafter.
Conclusion: The short-time increase in choroidal and optic nerve head blood flow indicates a transient vasodilatory effect of clonidine due to an unknown mechanism. The decrease in retinal blood flow indicates clonidine-induced vasoconstriction in the retinal microvasculature.
- alpha 2 agonist
- ocular blood flow