Eye Diseases Of Horses

The normal horse's eye is rich brown with the black pupil. A milky patch indicates cataract or some other form of ailment. Corneal ulcers and Uveitis are the most common eye diseases in horses. Corneal ulcers usually respond well to treatment. Sometimes they can be deep and require extensive surgery to preserve the horse's eye. Uveitis is an inflammation of the eye and causes much pain. It can occur along with the corneal ulcer and should be treated as soon as possible.

Corneal Ulcers

Cornea is a curved transparent portion of the eyeball that covers the iris and the pupil from penetration by dust and allows light into the eye. The iris is the colored part of the eye that controls the size of the pupil. The cornea contains almost no blood vessels, but many nurves. When the cornea is damaged by infection or trauma, a milky patch may appear which may result in loss of vision. Inflammation of the cornea may result from viral infections, such as equine influenza (a viral infection causing fever, coughing, and respiratory difficulty; some cause abortion in mares). The main causes of ulcers are infection, poor blood circulation, nerve damage, trauma, nutritional imbalances and cancers. Recent studies show that eye infections such as conjunctivitis, keratitis, and uveitis may be caused by the bacterium Listeria monocytogenes resulting from direct exposure of the eyes of susceptible animals to high numbers of the pathogen. Listeriosis affects wild and domestic animals as well as humans.

Corneal ulcers are infected wounds with potential risks to impair your horse vision if left untreated. Discharge from the affected eye with some builtup in the corner of the eyelid. The eyeball appears cloudy, fine red lines in the cornea which is normally clear. The eye might be very sensitive when the horse clamps down his eyelid. This is an emergency and you should call your veterinarian immediately.

[Photo of a horse eye]

Equine recurrent uveitis

Equine recurrent uveitis (ERU), also known as periodic ophthalmia or moon blindness, is one of the most common causes of blindness in horses. Classic treatment of ERU includes mydriatics, corticosteroids and nonsteroidal anti-inflammatory drugs. Despite vigorous topical and systemic treatment, however, in many cases, the prognosis for preserving vision remains poor. Despite extensive clinical research, the causes of equine recurrent uveitis (ERU) are still unknown. Recent studies show the presence of leptospires bacteria and antibodies in the affected horses. (Leptospirosis takes place by direct contact with urine of infected animals or by indirect contact with contaminated food or water).

Glaucoma is a disease associated with elevated pressure within the eye. Symptoms include cloudy cornea, dilated pupils, enlarged eyeball and inflammation of the iris. If left untreated, glaucoma leads to retina and optic nerve damage and blindness. The equine eye gets its nutrition from fluids that run through special pathways in and out.

Equine Multiple Congenital Ocular Anomalies

Equine Multiple Congenital Ocular Anomalies (MCOA) syndrome is a heritable eye disorder. Clinically, the disease manifests in two distinct classes depending on the horse type. Horses homozygous for the mutant allele have with a wide range of ocular defects, such as iris stromal hypoplasia (usually dark chocolate color), abnormal pectinate ligaments, megaloglobus, iridociliary cysts and cataracts. Heterozygous horses have iridociliary cysts.

The syndrome was first described in the Rocky Mountain Horse, where it is highly common, it is not limited to this breed. Additional horse breeds that have been diagnosed with MCOA syndrome include the Icelandic Horse, Shetland Pony, Exmoor Pony, American Miniature Horse, Belgian Draft and Morgan Horse, as well as the Kentucky Mountain Saddle Horse and Mountain Pleasure Horse, both of which are closely related to the Rocky Mountain Horse. The majority of MCOA syndrome horses also have the valued Silver coat color.1

Clinical signs of MCOA syndrome and a Silver colored Rocky Mountain Horse
Clinical signs of MCOA syndrome and a Silver colored Rocky Mountain Horse


  1. Equine Multiple Congenital Ocular Anomalies and Silver Coat Colour Result from the Pleiotropic Effects of Mutant PMEL. Lisa S. Andersson, Maria Wilbe, Agnese Viluma, Gus Cothran, Björn Ekesten, Susan Ewart, and Gabriella Lindgren