Figure 27: Vascular Supply of the Optic Nerve Head, Choroid and Retina

The ophthalmic artery is a branch of the internal carotid artery, which in turn, supplies the posterior ciliary (to choroid and outer retina) and central retinal (to inner retina) arteries. The central retinal artery (CRA) enters the optic nerve about 1 cm posterior to the globe, and an embolus may become lodged as the CRA pierces the dural sheath of the nerve, or posterior to the lamina cribosa, resulting in a CRA occlusion (CRAO, involvement of inner retinal layers, sparing of optic nerve head, outer retina and choroid). The arterial circle of Zinn-Haller supplies the optic nerve head, which is made up of anastomoses from branches of short posterior ciliary arteries (from posterior ciliary artery, PCA), the adjacent pial network, and choroidal vessels. Hypoperfusion of the PCA is the likely cause for non-arteritic anterior ischemic optic neuropathy. Ophthalmic artery pathology (e.g., thromboembolic, giant cell arteritis) results in ischemia of the retina, choroid, and optic nerve. (Redrawn and modified with permission from: Digre KB, Corbett JJ Practical Viewing of the optic Disc. Boston: Butterworth-Heineman 2003)