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.

Effect of ocular pressure on choroidal circulation in the cat and Rhesus monkey

Using the heated thermocouple principle to monitor blood flow-rate in the choroid of the anesthetized cat and Rhesus monkey revealed that elevation of ocular pressure reduces blood flow-rate in the choroidal circulation. The magnitude of this effect at varying levels of ocular pressure led to the conclusion that the vascular bed of the choroid in these experimental animals is a passive one without evidence of active regulation.

Optic nerve circulation and ocular pressure: contribution of central retinal artery and short posterior ciliary arteries and the effect on oxygen tension

Blood-flow rate in the optic nerve of the rhesus monkey 4 mm. behind the globe monitored by the heated thermocouple and tissue p02 measurement is found to be influenced by ocular pressure level. Ligation of central retinal artery reduced flow rate to 79 per cent of normal but did not influence the effect of IOP on blood-flow rate. Ligation of short posterior ciliary arteries reduced blood-flow rate to 21 per cent of normal and virtually eliminated the IOP effect. Raising IOP to above systolic arterial pressure level reduced blood-flow rate to 17 per cent of normal. At IOP levels greater than 50 mm. Hg, the reduction in blood-flow rate and in Po becomes marked and may be sufficient to produce primary lesions at this site.