Microvasculature of the raf optic nerve head

Purpose. Describe the arterial blood supply, capillary bed and venous drainage of the rat optic nerve head. Methods. Ocular rricrovascular castings of five Wistar rats were prepared by injection of epoxy resin through the common carotid arteries. Following polymerization, tissues were digested with 6M KOH and the castings washed, dried and coated for scanning electron microscopy. Results. The major arterial supply to the globe originates from the ophthalmic artery, which lies inferior to the optic nerve. Immediately posterior to the globe, the ophthalmic artery trifiacates into nasal and temporal long posterior ciliary arteries, vith the central retinal artery in between. The central retinal artery enters the globe inferior to the optic nerve head, but does not contribute to the capillaries of the nerve head. Arterioles to the optic nerve head arise from branches of the long posterior ciliary arteries that circle the optic nerve, analogous to the circle of Zinn-Haller in the prinate. These branches enter the choroid and arborize internal to the choroidal veins, >ending numerous arterioles into the capillary bed of the optic nerve head Capillaries supplying the neck and transition region of the optic nerve head drain, along with the central retinal veins, into several veins located around the perimeter of the optic nerve. These veins are also continuous with the choroidal veins, which drain the choriocapillaris along with the vortex veins Conclusion-4. The microvasular anatomy of the rat optic nerve head has numerous anatomic similarities to that of the primat 3, including a centripetal blood supply via the choroid from the posterior ciliary arteries &nd drainage into veins continuous with those of the retina. The close association of these veins with choroidal veins suggests that obstruction of vortex veins may significantly alter blood flow within the optic nerve head.