Short-term hemodynamic changes in episcleral arteriovenous anastomoses correlate with venous pressure and IOP changes in the albino rabbit.

In the present study we have determined the effects of acute diameter changes in the recently discovered episcleral arteriovenous anastomoses (AVA) on episcleral venous pressure and intraocular pressure (IOP) in the rabbit eye. The pressure was measured in episcleral arterioles, AVA and veins (vascular pressure) with a pressure chamber mounted on the tip of a microendoscope. After constriction of the AVA following topical administration (100 micrograms) of epinephrine we observed a decrease in the episcleral vascular pressure as well as in the IOP. Acute widening of the AVA after topical administration of 5mg nitroprusside led to a significant increase in the pressure of arterioles, AVA, veins and IOP which lasted several min. After 0.5mg topical nitroprusside the blood flow in the AVA increased. No significant effects were seen in the intravascular pressures; the IOP had a tendency to decrease. Experimental lowering of the IOP to 10mmHg caused an increase of vascular diameters and of blood flow in the AVA. It is assumed that-at least in drastic hemodynamic disorders-the degree of the AVA-perfusion might influence aqueous humor outflow and IOP due to changes of the episcleral venous pressure.