Anatomy of the ocular arteries in the horse.

The study examines the structure and functions of the ocular arteries in horses, highlighting variations in topographic arrangement and showing the various origins of intrabulbar arteries.

Study Design and Procedure

• The researchers carried out a detailed investigation of the ocular arteries in 20 equine eyes. The study utilized latex injections and methylmethacrylate casts which are methods used to replicate and study the structure of the vascular network.
• The objective of the study was to gain deeper knowledge of the ocular blood supply in horses, also discussing the differences and similarities with such supply in other species.

Findings on Ocular Arteries

• The study revealed that the orbital branches of the external ophthalmic artery, which serves the eye socket, emerge far behind the back part of the eyeball and do not have a consistent topographic arrangement, meaning their location and positioning may vary.
• The intrabulbar arteries (arteries within the eyeball) receive their blood supply from two other types of arteries: the ciliary arteries and the choroidoretinal arteries, both playing crucial roles in maintaining the health and function of the eye.

Different Ciliary Arteries

• The researchers observed subdivisions within the ciliary arteries, dependent on where they enter the eyeball. A posterior group enters the eye behind an imaginary line mid-way of the eye and an anterior group that enters in front.
• The posterior ciliary arteries comprise four main vessels. These vessels enter the eyeball’s walls in four different positions, namely lateral, medial, dorsal, and ventral. The lateral and medial arteries continue on a long path within the eyeball after supplying several short posterior ciliary arteries to the choroid.
• The anterior ciliary arteries consist of a dorsal and ventral vessels that enter the eyeball near the cornea.

Choroidoretinal Arteries and Iridic Arterial Circle

• The choroidoretinal arteries form an arterial network around the optic nerve at the back of the eyeball, providing blood to all retinal arterioles and some branches close to the optic disc in the choroid. The major part of the choroid gets its blood supply from the posterior ciliary arteries.
• Interestingly, the iris contains a significant arterial circle created by the lateral and medial long posterior ciliary arteries and both anterior ciliary arteries. However, neither a minor iridic arterial circle nor a central retinal artery was found in the examined equine eyes, highlighting specific characteristics of the ocular blood supply in horses.