Blood flow autoregulation may be deficient in patients with glaucoma, making the optic nerve circulation susceptible to the challenge of intraocular pressure (IOP). Adequacy or inadequacy of autoregulation may be a factor that decides whether a patient with elevated IOP develops glaucomatous optic nerve damage. Hypothetically, capillaries may assist arteries and veins in the regulation of blood flow. Our attention has become focused on the pericytes, particularly abundant in the optic nerve and retina, which are a contractile component of capillaries and may therefore be the cells responsible for the capillary’s role in autoregulation.