Nine out of 10 persons have a collateral blood supply to the orbit adequate to prevent permanent blindness after a major obstruction of the internal carotid artery or the ophthalmic artery.26 Certainly the ophthalmic artery is the principal vessel to the orbit, however, its dominance has been overemphasized.
There are 5 orbital sites of anastomosis between branches of the internal carotid artery and those of the external carotid artery. All 5 of these collateral channels are described but not emphasized in current textbooks. Collateral circulation to the orbit was illustrated in the human by Soemmerring1 in 1818, described by DuBrueil2 in 1847, and discussed at length by Meyer3 in 1887. Other authors4-15 between 1874 and the present time have augmented our knowledge. Interest increased as the clinical significance of these collateral pathways in maintaining the circulation to the retina became apparent.
Virchow16 and Fraenkel
GILLILAN LA. The Collateral Circulation of the Human Orbit. Arch Ophthalmol. 1961;65(5):684-694. doi:10.1001/archopht.1961.01840020686015