Horses with Moon Blindness

View of horse's head, eyes and ears.

Moon blindness is an inflammatory eye ailment named by its erroneous connection with the phases of the moon. Moon blindness is now known to have nothing to do with the moon and can reoccur throughout weeks or months. It causes eye irritation and discolouration, and horses with it are extremely sensitive to intense sunshine. Appaloosas, in particular, appear to be more vulnerable than other horse breeds. Owners should seek medical treatment as soon as symptoms occur since this ailment is progressive and can lead to blindness.

What Is Moon Blindness?

Moon blindness, also known as equine recurrent uveitis (ERU), is a kind of autoimmune disease characterized by recurring inflammatory episodes in one or both eyes. It's the most prevalent cause of horse blindness.

Symptoms of Moon Blindness

Symptoms of moon blindness involve one or both eyes. A horse will be reluctant to be in bright sunlight, exhibiting signs of pain or irritation that are not relieved by antibiotic treatment.


  • Inflammation
  • Redness of the eye area
  • Murkiness or white discoloration of the eye
  • Tearing (watering)
  • Squinting
  • Blindness

Moon blind horses may experience recurring bouts of inflammation followed by periods of relative painlessness. Others have chronic low-grade inflammation. Owners may attribute redness, weeping, and squinting to an irritant in the surroundings or an infection in the eye, but treatments for these problems will have no influence on moon blindness.

Moon blindness is classified as recurring since it seems to clear up before returning on its own. Recurrence may take years for some horses, while flare-ups may happen much more often, with episodes lasting weeks or even days.

Untreated, moon blindness can lead to cataract formation or prolonged inflammation, both of which are likely to lead to permanent blindness.

Causes of Moon Blindness

There are several possible causes for moon blindness, although a genetic predisposition to autoimmunity probably underlies external triggers, which may include:

  • Bacteria (leptospirosis)
  • Vitamin deficiencies
  • Physical injuries
  • Equine flu
  • Tooth and

Appaloosas and German warmbloods are two breeds that seem particularly vulnerable to moon blindness due to hereditary factors.

Diagnosing Moon Blindness in Horses

Your veterinarian will evaluate the horse's recent ocular health history when diagnosing moon blindness. Moon blindness is indicated by recurrent episodes of inflammation, which helps rule out other eye disorders. In addition, your veterinarian will do a thorough eye examination, including a fluorescein stain, to assess the health of the cornea and retina.

Treatment for Moon Blindness

For inflammation and discomfort, moon blindness can be treated with steroids, nonsteroidal anti-inflammatory medications (NSAIDs), and mydriatics. It's critical to shield your horse from strong light during an intense flare of moon blindness by wearing a mask or keeping it indoors.

You will need to restart therapy if this issue recurs. Some horse owners may resort to euthanasia due to frequent flare-ups. Only one eye can be removed if it is damaged. Although surgery to implant a drug-laden disc in the eyes appears to have some potential, it is not yet widely used.

Prognosis for Horses with Moon Blindness

Although there is no cure for moon blindness, early therapy can help delay the disease's progression. More than half of horses suffering from moon blindness will eventually go blind.


Although there is nothing that can be done to avoid moon blindness, adequate diet, a clean environment, fly control, and vigilant care can help your horse live as long as possible. If you see eye irritation or discharge, contact your veterinarian right away so that treatment may begin.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.


"Equine Recurrent Uveitis. UC Davis Veterinary Medicine Center for Equine Health." ;