Occlusion of the posterior ciliary artery. 3. Effects on the optic nerve head.

The two or three posterior ciliary arteries (medial and lateral posterior ciliary arteries), which are the source of blood supply to the posterior choroid, are also the major souice of blood supply to the optic nerve head (Hayreh, i969, I970) and have a segmental distribution (Hayreh, I970, I97ib). The ciliary circulation is the only source of blood supply to the lamina cribrosa and prelaminar regions, and it is an important if not the only source of supply to the retrolaminar part of the optic nerve. Hayreh (i 969, I 97 I a) put forward the view based on these studies that ischaemic optic neuropathy is produced by acute occlusion of the posterior ciliary arteries (PCAs). The effects ofacute occlusion of the PCAs on the optic nerve head have been investigated experimentally in rhesus monkeys. These produced a clinical and histopathological picture of ischaemic optic neuropathy. Intravenous fluorescence fundus angiography (IVFA) studies of patients with ischaemic optic neuropathy have further confirmed the presence of occlusion of the PCAs.