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D. R. Anderson, R. W. Knighton; Recovery From Abruptly Decreased and Abruptly Increased Blood Flow in the Human Optic Nerve Head Induced by Changes in Intraocular Pressure. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3443.
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Regulation of blood flow in the optic nerve has been shown in animals. In a previous study in humans, 8 of 10 normal eyes maintained blood flow with gradual incremental increase of intraocular pressure (IOP) until arterial pressure was reached. In the present study, blood flow was studied after abrupt elevation and later abrupt lowering of IOP.
In the eye of the 10 subjects studied before, capillary blood flow of the optic nerve head was measured with laser Doppler flowmetry. After a baseline reading, a suction cup was placed on the temporal sclera. With the patient positioned comfortably, the IOP was raised 38 mm Hg above baseline. Blood flow was measured for 5 min, every 30 sec for 2 min and then every 60 sec. The suction was released. Starting at 400 sec, blood flow was measured every 60 sec for 5 min.
In all subjects abrupt elevation of IOP caused abrupt reduction in flow. In 8 of 10 subjects flow returned to baseline over 5 minutes, but remained depressed in the other two, the same two that had shown failure to maintain flow with slow elevation of IOP. With release of the elevated IOP, rebound overperfusion occurred with gradual decline to baseline over 5 minutes in all 10 subjects. The figure shows the average blood flow (of all 10 subjects) normalized to baseline.
Two of 8 subjects failed to restore flow to normal levels with elevation of IOP, the approximate proportion of individuals who develop glaucoma rather than remain undamaged with ocular hypertension. However, all subjects showed rebound hyperperfusion, so stimuli to increase blood flow were present, and failure to restore flow fully is unexplained. The time for recovery from hypoperfusion or hyperperfusion is about 5 minutes.
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