Anatomy of the ocular arteries in the horse.

Orbital and intrabulbar arteries were studied in 20 equine eyes by means of latex injections and methylmethacrylate casts. The orbital branches of the external ophthalmic artery arise far caudal to the posterior pole of the eyeball and present a variable topographic arrangement. The intrabulbar arteries are supplied by ciliary and choroidoretinal arteries. Dependent on their entrance into the eyeball, the ciliary arteries are subdivided into a posterior and an anterior group. The posterior ciliary arteries perforate the sclera post equatorially and consist of 4 major vessels that penetrate in the lateral, medial, dorsal and ventral meridian of the eyeball, respectively. The lateral and medial of these arteries follow a long intrabulbar trajectory after having supplied several short posterior ciliary arteries to the choroid. The anterior ciliary arteries consist of a dorsal and a ventral vessel which penetrate the eyeball in the pericorneal area. The choroidoretinal arteries form an arterial network around the optic nerve at the posterior pole of the eyeball. They give rise to all retinal arterioles and some peridiscal choroidal branches. The larger part of the choroid is supplied by branches of the posterior ciliary arteries. Additionally, the anterior choroid receives recurrent branches from an arterial circle that lies externally in the ciliary ring. The iris contains a major arterial circle formed by the lateral and medial long posterior ciliary arteries and both anterior ciliary arteries. A minor iridic arterial circle nor central retinal artery could be found in the equine eyes examined.