Pressure and Optic Nerve Damage:

How does pressure damage the optic nerve? The importance of ocular blood flow:

There are two theories as to how pressure damages the optic nerve.

The first is the structural theory. According to this theory, high pressure impinges on the optic nerve and its surrounding support structure (laminose cribosa). The high pressure causes a breakdown in axoplasmic flow or has other unknown biomechanical affects that lead to death of axons (there are 1.2 million axons per nerve).

The second theory is the vascular theory. We know that when eye pressure rises this can reduce the blood flow to the optic nerve and compromise oxygen flow. In a normal patient the small blood vessels will enlarge (dilate), and this will supply more oxygen into the nerve (vasodilation). In patients with glaucoma, the normal (vascular) response does NOT occur, and the tissue is deprived of the oxygen it needs to maintain itself. According to the vascular theory, glaucoma may be a vascular disease that initially reduces the size and number of choroidal blood vessels.

To help determine which patients might have vascular (circulatory) impairment of the blood flow to their eyes, we employ a Blood Flow Analyzer (BFA). The BFA records retinal and choroidal blood flow by measuring eye pressure variations over time at a rate of 200 samples per second. It measures differences in blood flow to the eye during different phases of the heart’s rhythm; recording the increase in systole and the decrease in diastole. Patients with low blood readings are considered at higher risk for glaucoma.

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