The 1994 Von Sallman Lecture. The optic nerve head circulation in health and disease

This is a brief overview of multifaceted anatomical, experimental and clinical studies conducted by the author since 1955 on the optic nerve head circulation in health and disease. Conclusions, based on the accumulated information provided by these studies, are summarized. The studies on the pattern of blood supply of the optic nerve head have shown that: (a) its main source of blood supply is the posterior ciliary artery circulation, with retinal circulation supplying only the surface nerve fiber layer, (b) there is marked interindividual variation in the blood supply pattern, and (c) the blood supply in the optic nerve head has a sectorial distribution. The various factors which produce interindividual variation in the blood supply of the optic nerve head are discussed, particularly those in the posterior ciliary artery circulation; this is because all available evidence indicates that it is derangement in the posterior ciliary circulation in the optic nerve head that is primarily responsible for the common ischemic disorders of the optic nerve head, e.g. anterior ischemic optic neuropathy and glaucomatous optic neuropathy. Factors that may derange the blood flow in the optic nerve head include defective autoregulation of blood flow in it, vascular changes in its feeding arteries, hematologic abnormalities, systemic arterial hypertension and hypotension, and intraocular pressure; their roles are discussed. For better understanding and management of optic nerve head ischemic disorders, there is an urgent need for an accurate clinical method of assessment of blood flow in the posterior ciliary circulation in optic nerve head, since no satisfactory method is currently available. Redness or pallor of the optic disk on ophthalmoscopy is not a true guide to the optic nerve head vascularity as it gives no information about the state of the posterior ciliary circulation. Fluorescein fundus angiography, though far superior to the optic disk color for evaluation of optic nerve head vascularity, has a number of limitations. All these topics and various controversies about them are discussed briefly.