1.NounEither of usually two arteries of which one arises from the ophthalmic artery on each side of the optic nerve, passes forward along the optic nerve accompanying the short posterior ciliary arteries, pierces the sclera passing forward on the same side of the eyeball between the sclera and the choroid to the ciliary muscle, and at the junction of the ciliary process and the iris divides into upper and lower branches which anastomose with the branches of the contralateral artery to form a ring of arteries around the iris.