Tuesday, December 14, 2010

Ciliary Arteries

The ciliary arteries are the blood vessels which supply blood to the choroid, which is the vascular layer of the eyeball, the ciliary body, the iris, the conjunctiva, and the sclera. Branching off the ophthalmic artery, the ciliary arteries are divisible into three groups: 1) the long posterior; 2) short posterior; 3) the anterior.

1) The long posterior ciliary arteries are the two blood vessels which supply the iris, ciliary body and choroid. They pierce the posterior part of the sclera at some little distance from the optic nerve, running forward along either side of the eyeball, between the sclera and choroid, to the ciliary muscle, where they divide into two branches. Here the long posterior ciliary arteries form an arterial circle, the circulus arteriosus major, around the circumference of the iris, from which numerous converging branches run, in the substance of the iris, to its pupillary margin, where they form a second (incomplete) arterial circle, the circulus arteriosus minor.

2) The short posterior ciliary arteries, from six to twelve in number, arise from the ophthalmic as it crosses the optic nerve. They pass forward around the optic nerve to the posterior part of the eyeball, pierce the sclera around the entrance of the optic nerve, and supply the choroid (up to the equator of the eye) and ciliary processes. Some branches of the short posterior ciliary arteries also supply the optic disc via an anastomotic ring, the Circle of Zinn-Haller or Circle of Zinn, which is associated with the fibrous extension of the ocular tendons (Annulus of Zinn).

3) The anterior ciliary arteries are the seven blood vessels which derive from the muscular branches of the ophthalmic artery. These arteries supply the conjunctiva and sclera. They run to the front of the eyeball in company with the extraocular muscles, form a vascular zone beneath the conjunctiva, and then pierce the sclera a short distance from the cornea and end in the circulus arteriosus major. 2 Ciliary Arteries stem from each rectus muscle except the lateral rectus.