Ocular effects of clonidine in cats and monkeys ( Macaca irus)

Abstract

In monkeys administration of about 0·01 μg clonidine into the anterior chamber caused no significant change in the facility of outflow. At 10 μg/kg body weight given intravenously the facility decreased by 0·09±0·01 μl · min −1 · mmHg −1 from a level of 0·51±0·05 μl · min −1 · mmHg −1. The same dose had no significant effect on the rate of aqueous humor formation determined with an indicator dilution technique. Before the administration of the drug the formation of aqueous humor was 1·43±0·13 μl/min, and 30 min later it was 1·32±0·15 μl/min. The fall in eye pressure was 1·0±0·3 mmHg. In cats 2–10 μg/kg body weight clonidine given intravenously reduced the intrascleral venous pressure and the eye pressure in a way which indicated marked vasoconstriction in the eye. Unilateral carotid injection of the drug at a dose reducing the homolateral eye pressure by 4–5 mmHg caused a 19% reduction in the choroidal blood flow, a 34% reduction in the blood flow through the iris and a 42% reduction in the blood flow in the ciliary body when the injected side was compared to the other.