PURPOSE

To measure orbital venous pressure (OVP) and determine the effects of changes in mean arterial pressure (MAP) on OVP, intraocular pressure (IOP), episcleral venous pressure (EVP), and ciliary and choroidal blood flows.

METHODS

The experiments were performed in anesthetized rabbits. In all animals, MAP, IOP, and OVP were measured by direct cannulation of the central ear artery, the vitreous, and the orbital venous sinus, respectively. Laser Doppler flowmetry was used to measure choroidal blood flow in one group, and ciliary blood flow in a second group. A servonull micropressure system was used to measure EVP in a third group. The protocol for all three groups entailed varying MAP mechanically with occluders on the aorta and vena cava.

RESULTS

The OVP and IOP relationship correlated linearly (r = 0.99) during mechanical manipulation of MAP. EVP also correlated well with OVP (r = 0.9). Resistance calculations based on choroidal and ciliary blood flows and the pressure gradients indicate active adjustment of arterial resistance and passive changes in venous resistance in response to changing MAP in both circulations.

CONCLUSIONS

The rabbit orbital venous sinus permits continuous measurements of OVP. The present findings show that OVP is not static and suggest that OVP may play an important role in IOP homeostasis and ocular hemodynamics.