Optic nerve circulation and ocular pressure

Rapid, short-lasting elevation of ocular pressure level produces simultaneous reduction in blood-flow rate in the distal 6 mm. of the extraocular portion of the optic nerve of the rhesus monkey as monitored by the heated thermocouple technique. The magnitude of this reduction was very small until intraocular pressure (IOP) exceeded 50 mm. Hg following which markedly and progressively greater reduction in blood-flow rate occurred at higher IOP levels; maximum reduction was reached at IOP of 105 mm. Hg. The magnitude of reduction in blood-flow rate for each ocular pressure level was significantly greater when systemic arterial pressure was reduced. These effects were monitored 2 to 4 mm. behind the globe and became reduced at a more proximal location, disappearing at locations further than 6 mm. from the globe. The results suggested a reduction in nutrient blood flow to the optic nerve at the monitored site with elevation of IOP.