Intracranial Pressure and Ocular Hemodynamics

In owl monkeys, controlled elevation of subarachnoid pressure was produced either intracranially, in the optic nerve sheath, or in both. When intracranial pressure was elevated, orbital venous pressure became elevated, but it did not keep pace with intracranial pressure elevation, because orbital veins have anastomoses to facial veins and need not depend entirely on cavernous sinus for drainage. The central retinal vein pressure is additionally affected by pressure in optic nerve sheaths, and keeps pace with vaginal sheath pressure elevation, because anastomotic connections at the optic disc between central retinal vein and vortex vein were not sufficient to relieve fully pressure in the central retinal vein. Intraocular blood flow was slowed in regions drained by central retinal vein (retina and disc). The choroidal flow, which drains via vortex veins into orbital veins, was affected less.