Effects of Dopamine on Ciliary Blood Flow, Aqueous Production, and Intraocular Pressure in Rabbits

Dopamine is a known modulator of cardiovascular function and intraocular pressure (IOP). In this study, the authors investigate the dose-dependent effects of dopamine on IOP, ciliary hemodynamics, and aqueous production in anesthetized rabbits to test the hypothesis that aqueous production becomes blood-flow-dependent if ciliary perfusion declines below some unknown critical level. Two protocols were performed. In the first protocol, mean arterial pressure (MAP) and IOP were measured by direct cannulation, and ciliary blood flow was measured transsclerally by laser Doppler flowmetry, while MAP was varied mechanically over a wide range before and during intravenous dopamine infusion (40 microg/min, n = 8; 80 microg/min, n = 10; 600 microg/min, n = 7; 1800 microg/min, n = 5). In the second protocol, MAP and IOP were measured by direct cannulation, and aqueous flow was measured by fluorophotometry, before and during intravenous dopamine infusion (40 microg/min, n = 8; 600 microg/min, n = 11). The low infusion rate shifted the ciliary pressure flow curves upward and increased aqueous production (40 microg/min), whereas the higher infusion rates shifted the pressure flow curves downward (600 and 1800 microg/min) and decreased aqueous production (600 microg/min). All infusion rates decreased IOP. Dopamine causes dose-dependent, parallel changes in ciliary blood flow and aqueous production, with ciliary vasodilation and secretory stimulation at the lowest infusion rate and vasoconstriction and secretory inhibition at higher infusion rates. Dopamine also significantly lowers IOP.