This condition, also known as “moon blindness,” is the main cause of blindness in horses. The uveal tract, consisting of the iris and adjacent structures, is the main blood supply of the eye. Toxic, immunologic and/or infections agents in the blood damage the blood vessels of the eye and then can indirectly affect most other parts of the eye. These agents can cause temporary damage but also can cause low-grade, slow destruction of the eye. Inflammation of the eye can be quite obvious or can be subtle, resulting in underlying damage without obvious signs. This initial blood vessel reaction in the iris can recur repeatedly.
What causes Uveitis?
Specific causes of recurrent uveitis have not been clearly defined. The bacterium Leptospira and the parasite Onchocerca have been implicated in a few cases. The disease may not result from direct infection by these agents but from immune (allergic) reactions to these agents. Breed predispositions are also noted with Appaloosa and Paint breeds being highly represented.
Mild cases: Tearing, increased blinking, some swelling of the eyelids.
Severe cases: Closure of the eyelids from swelling and/or pain, haziness or clouding of the cornea (corneal edema), tearing, and constriction of the pupil.
Chronic cases: Damage to the lens and subesquent fibrin deposition and luxation of the lens, collapse of the anterior chamber and permanent blindness.
Important Points in Treatment
Treatment is directed at reducing these reactions in an effort to minimize future scarring. Common therapy includes a combination of topical and systemic medication including: topical atropine, anti-inflammatories (including steroids), and antibiotics, systemic non-steroidal anti-inflammatories and occasionally oral doxycycline antibiotics. It is important that the horse be examined by a veterinarian to accurately diagnose this condition and rule out the presence of a corneal ulcer, laceration or abcess as these conditions are very serious and could be made worse by treatment for uveitis.
Watch for improvement, such as reduced tearing and swelling, and wider opening of the eyelids. A flashlight can be used to see if the pupil is open. Early treatment is critical. Once treatment has been initiated the horse should start to be more comfortable within a day or so. Call the veterinarian if signs of improvement are not evident within 2-3 days.
Apply hot packs. Soak a towel or wash cloth in water as hot as your hand can tolerate, squeeze out the excess water and apply the hot pack to the eye for 10 minutes. Your horse may lean into the compress because of its comforting effect. The hot pack also makes it easier to apply medication to the eye.
Apply a fly mask to keep insects away from your horse’s eyes.
Keep your horse out of the sun and away from any significant amount of direct light. This is due to the pupillary dilation effect of the atropine.
If your horse begins to rub its eye, some restraint may be necessary, such as an eye cup. Rubbing can further damage an already damaged eye or create an additional problem like a corneal ulcer which needs to be treated differently and even be made much worse by the treatment for uveitis.