Common Problems of the Equine Eye

By R. Paul Schwab, D.V.M.

Kulshan Veterinary Hospital

            As the ground gets drier and the flies get more aggressive, horse eyes can take a beating.  During the late summer and early fall months we usually treat several horses a week just for eye problems.  This article will discuss some of the more common conditions of the equine eye and hopefully help you determine when veterinary care may be needed.

            Knowing the anatomy of the eye is important, especially if you call for advice from your veterinarian.  Describing where the problem is or what part of the eye is abnormal looking is very helpful.  The conjunctiva is the pink membrane that lines the inside of the eyelid and also covers the sclera, which is the white part of the eyeball itself.  The cornea is the clear outer lining of the eyeball that you look through to see the iris, pupil, and lens.  The iris is the colored membrane (usually brown in horses) that forms the pupil, or hole in which light can penetrate to the lens and eventually the retina.  The retina is membrane in the back of the eye that contains all the light sensitive nerve tissue.  Horses also have a structure on their iris called a corpora nigra, which looks like a small rock on the top and bottom of the iris.

            Conjunctivitis means inflammation of the conjunctiva usually the result of some form of irritant.  A horse with mild conjunctivitis will have mild reddening of the inside of the eyelids and sclera.  (See above anatomy lesson in paragraph two).  They usually have some tearing in the eye or both eyes.  This is the common condition we see in late summer and early fall with the arrival of dust, flies, wind, and other allergens.  Horses with mild conjunctivitis do not generally have swollen eyelids and do not appear to be in pain. (Pain appears as squinting of the eye to attempt to keep it closed).  Treatment consists of cleaning the eye and face and flushing the eye out with sterile saline solution.  Fly control in the form of insecticides and or fly masks are a must.  If this treatment does not correct the problem, veterinary assistance may be needed.

            More severe conjunctivitis consists of tearing, reddening of the conjunctiva, and some pain and swelling of the eyelids.  These horses should be seen be a veterinarian to rule out the possibility of infection, foreign body in the eye, and involvement of the cornea.  If the cornea is involved it is called keratoconjunctivitis.   If the cornea is affected, whether by abrasion, puncture, or severe infection there may be a cloudy area or roughened area on the clear portion of the eye.  This is not always the case.  Some very severe corneal abrasions can go unnoticed with the naked eye, especially those caused by chemical irritants.   If your veterinarian comes to look at your horse’s eye, one of the first things they will do is stain the cornea with a fluorescein dye.  If there is a defect in the cornea, it will show up as a bright green area on the eye.  These lesions can be very serious if not treated early.  We generally use antibiotic ointments in the eye as well as anti-inflammatory drugs such as phenylbutazone or Banamine. 

            Some horses with “goopy eyes” actually have clogged tear ducts.  Most animals drain their tears through a tiny hole in the inside corner of the eyelids.  This hole connects through a tiny tube in the skull to an opening in the nose.  This is why your nose runs if you cry.  Often times this hole gets plugged with debris and has to be flushed out.  The typical horse with a plugged tear duct has goopy eyes all the time, but the eye itself looks fine despite frequent cleaning.

            Another common condition of the equine is anterior uveitis.  Uveitis is inflammation of the structures in the front chamber of the eye (iris, cornea, lens, etc.).  This may be caused by severe infection, trauma to the eye, surgery, corneal ulcers, or immune disorders.  Anterior uveitis can develop into a syndrome called recurrent uveitis in which the inflammation comes and goes.  “Moon blindness” is common name for this condition because it was once thought to have something to do with the phases of the moon.  It’s now thought to be an immune mediated problem.   Horses with anterior uveitis are very painful and the cornea is usually completely cloudy.  This is a very serious condition and should be treated promptly.   We generally use topical steroids, systemic antiinflammatories and possibly even systemic antibiotics.  Moon blindness can be a very frustrating disease because of its recurring nature.  Eye removal may be needed in non-responsive cases.