Moon Blindness (Uveitis) in Horses

This condition, known more commonly as moon blindness, is an affliction of the horses' eye. It can occur in one or both eyes.

Also called periodic ophthalmia or chronic intraocular inflammation, the cause can be a number of possible irritations or infections. One cause is believed to be the bacteria leptospirosis.

It is painful to the horse, and as the name implies, returns over time -- resulting in eventual blindness.

photos: top, normal eye; bottom, cloudy eye with drainage and squinting

Watch for these most common signs:

• increased tearing (clear drainage from eye)

• squinting

• redness or swelling of the tissues surrounding the eye

• cloudiness or discoloration of the eye

The horse may not appear to be in pain, however, glaucoma causes a "headache" type feeling, and should be treated without undue delay. You should not expect your horse to perform at his best with a constant untreated migrane any more than you could.

photo: cloudy affected eye

Your regular veterinarian may refer you to an equine ophthalmologist. It is very important to measure the amount of pressure inside the eye (intraocular) and most general practice vets do not have the equipment to do so. Blood tests may also be advised.

Prognosis is fair to poor in terms of vision loss. Appaloosas seem especially prone to blindness due to ERU. Treatment can provide comfort and prolong vision in most cases. Treating moon blindness is a lifetime commitment; there is no cure.

Topical ointments are commonly prescribed for treatment up until a time which significant vision loss has occured. Each attack of uveitis adds to the previous damage, so it is important to continue treatment even when no physical signs are present.

photo: top, normal eye; bottom, cloudy eye without drainage

ERU can also cause secondary glaucoma to develop. This increased pressure inside the eye is both uncomfortable and blinding. If glaucoma does develop, the eye will likely need to be removed. This surgery is known as enucleation.

Surgery is costly. Many owners will opt to have the horse humanely destroyed, rather than have it endure the constant discomfort or try to accommodate a blind horse.

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