Investigating brood flow autoregulation in the optic nerve is important to
understand the physiopathology of Various ocular diseases such as glaucoma.
This investigation requires that one establishes the relationship between
optic nerve blood now and perfusion pressure. Previous work has documented
the effect of lowering the perfusion pressure on optic nerve blood flow. Th
e purpose of the present study was to investigate the effect of elevated pe
rfusion pressure on blood flow in this tissue.
Laser Doppler flowmetry was applied to measure relative mean velocity, volu
me and flux of red blood cells in the tissue of the optic nerve head. These
parameters were measured in 13 subjects during isometric exercise consisti
ng of squatting.
In the range of perfusion pressures from 56 +/- 4 to 80 +/- 5 mmHg (30 +/-
8%), there was no significant variation of mean velocity, Volume and flux o
f red blood cells, but vascular resistance increased by about 50%. Intraocu
lar pressure was increased significantly above baseline at the end of squat
ting and decreased during recovery.
The results suggest that the maintenance of constant blood flow is achieved
by an increase in Vascular resistance taking place either at the arteriole
s feeding or at the veins draining the blood from the ONH or at the ophthal
mic artery and/or vessels between this artery and the site of LDE measureme
nts. Combining the results of this study with those of a previous one where
perfusion pressure was decreased by increasing the intraocular pressure, w
e show the entire relationship between perfusion pressure and optic nerve b
lood now in man. (C) 1998 Academic Press.