Orbital vascular anatomy.

The anatomy of the orbital vascular bed is highly complex, with tremendous interindividual variations. The main source of blood supply to the orbit is by the ophthalmic artery, the first branch of the internal carotid artery. The origin, course, and branches of the ophthalmic artery, and the genesis of the variations in origin, course, and branching pattern of the ophthalmic artery are discussed. The external carotid artery normally contributes only to a small extent to the orbital blood supply via the infraorbital artery and orbital branch of the middle meningeal artery.The complex, highly variable and confusing orbital venous system can be divided into: (i) main orbital veins (superior and inferior ophthalmic veins), (ii) inconstant orbital veins (middle and medial ophthalmic veins and four collateral veins), (iii) orbital venous networks, and (iv) various venous tributaries. All these are described briefly.