Moon blindness in horses

Moon blindness in horses
Moon blindness in horses

Lunar blindness, a painful condition of the eye, was called that because it seemed to occur with the phases of the moon. We now know that lunar blindness can occur over a period of days, weeks, months or years and has nothing to do with the moon. A diagnosis of blindness to the moon is painful for both the horse and the owner since sometimes it is necessary to make difficult decisions to avoid prolonging the horse’s continuous pain. Some breeds seem to be more susceptible than others. Appaloosas, in particular, seem to develop moon blindness more commonly than other races. If you suspect lunar blindness, call your veterinarian, since a quick diagnosis is important for the comfort of your horse.

Other names for lunar blindness

Like many diseases and conditions, there are many names for lunar blindness. Other names for humor blindness are recurrent equine uveitis, periodic ophthalmia, ERU, periodic ophthalmia or chronic intraocular inflammation.

Causes of Moon Blindness

There are several possible causes for lunar blindness or recurrent equine uveitis. Bacteria, fungi, viruses, parasites, pollen, vitamin deficiencies, autoimmune deficiencies, and physical injuries can be the cause of blindness to the moon. Bacteria of leptospirosis and bacteria that cause strangulation can be two of the most common bacterial causes. Abs of equine flu, teeth and hooves can also cause lunar blindness. If there is a parasite connection, the blindness of the moon can be caused by an antiparasitic medication.

Lunar blindness is considered recurrent because it seems to clear up and then reappears spontaneously. For some horses, recurrence can occur over a period of years or outbreaks can occur much more frequently, episodes occur in weeks or even days.

Symptoms of Blindness to the Moon

Symptoms of blindness to the moon include swelling and redness of the eye area, turbidity or white discoloration of the eyes, tearing, squinting and profuse but clear lachrymation. The horse will be reluctant to be in the sunlight. Although it may not be obvious, the horse will feel pain from the symptoms. The ERU can affect one or both eyes. Your veterinarian will examine your horse’s eyes to determine what internal structures are affected, to distinguish it from a “simple” eye infection.

Effects of the ERU

In addition to the obvious symptoms evident in the eye and the area, total blindness can follow if the horse is not treated properly and without delay. Certainly, subsequent outbreaks will cause pain and, unfortunately, there is nothing that can be done to prevent further episodes when symptoms are not present. Cataracts can develop, causing blindness. Internally, the structures of the eye can be damaged.

Treatment for lunar blindness

Because your horse will experience discomfort due to symptoms of lunar blindness, you should call your veterinarian, who will confirm the diagnosis and suggest treatment. The treatment will probably include steroids and medications that will help dilate the horse’s pupil. You will want to protect your horse from bright light with a mask or by keeping it inside. Each time the condition reoccurs, you must resume treatment. Unfortunately, if the condition returns too often, many horse owners may resort to human euthanasia instead of letting their horses suffer the pain of outbreaks. If only one eye is involved, the eye can be removed. Surgery to implant a disc loaded with medication in the eyes seems to be promising, but it is still not common.


Unfortunately, there is little that can be done to prevent lunar blindness, mainly because we do not know what will cause the condition in any particular horse. The best we can do is provide good nutrition, a clean and healthy environment, fly control and attentive care. When you see that your horse has an eye infection, call your veterinarian. Eyes are difficult to treat, so make sure that if a treatment is required, start quickly before a major infection appears.


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