Effects of raised intraocular pressure on retinal, prelaminar, laminar, and retrolaminar optic nerve blood flow in monkeys.

Effects of increments in intraocular pressure on the blood flow in the retina and. the distal part oj the optic nerve were investigated in monkeys with the use of untabeled microspheres. Moderate elevations in intraocular pressure which reduced the perfusion pressure (mean arterial blood, pressure — intraocular pressure) to levels above 40 cm H2O had only small effects in the retina and. the preliminar part oj the optic nerve. In the laminar and retrolaminar parts, there was normal flow. At perfusion pressures less than 40 cm H2O, retinal and prelaminar flow was proportional to the perfusion pressure. Retrolaminar flow tended, to increase with decreasing perfusion pressure. At very high intraocular pressures which stopped, blood flow in the retina and the prelaminar part of the optic nerve, there was a marked redistribution oj the blood flow in the laminar region, the anterior portion being underperfused. and the posterior overperfused. Close retrolaminar flow was increased; farther posteriorly flow was normal. After a period of ocular ischemia, there was marked reactive hyperemia in the retina and prelaminar and laminar parts of the optic nerve. No simple vascular explanation was found, in monkeys for the degeneration of the optic nerve in glaucoma and the blockage of axoplasmic flow within the posterior part of lamina cribrosa in experimental ocular hypertension.