Control Mechanisms of Retinal Vein Pressure: Evaluation in the Cat Using an In Situ Infusion Micropipette

Abstract

Vein pressure in the cat retina is maintained above intraocular pressure by mechanisms other than active control. A passive high-resistance segment resides somewhere within the optic nerve possibly within the lamina cribosa or prelaminar region.

A pilot study of in vivo venous pressures in the pig retinal circulation

“…It has been suggested that as IOP rises the accompanying mechanical responses of the tissues around the lamina cribrosa compress the vein, and outflow resistance is increased 1,5,9 . This theory is supported by the observations that variation in IOP causes movement of the optic disc 11 and lamina cribrosa, 12 and that reversal of cupping is seen following trabeculectomy 13,14 …”

“…Increased IOP is accompanied by a reduction in ocular blood flow, 10 so outflow resistance must increase as IOP increases to allow retinal venous pressure to follow changes in IOP. Attariwala et al found no evidence for active venous responses to account for this relationship and concluded that outflow resistance changes passively in response to IOP changes 1 …”

“…The underlying mechanism for the control of venous outflow has been the subject of controversy, 1 and there is marked variation in the measured values for transmural venous pressure obtained in animal experiments 2,3 . Our aim was to study intravascular pressure within the pig retinal venous system using a balanced servo‐nulling micropuncture technique, as described by Weiderhielm 4 .…”