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Moon Blindness

I have an Appaloosa/Paint mix, and my farrier once mentioned to me to be careful about moon blindness. What is it, what breeds does it affect, what can be done to prevent it, and once it’s contracted, what are the treatment options? Since my horse is a mix, is he less likely to contract moon blindness? – via

To make sure I cover all your questions, let’s tackle them one at a time.

What is it?
“Moon Blindness” is technically known as Equine Recurrent Uveitis, which means that it occurs in horses, is a chronic condition, and causes inflammation (“itis”) of the uvea, or inner structures of the eye. It is one of the most common eye conditions of horses and the leading cause of equine blindness. It gets its name from the waxing and waning course of the disease, where active bouts of inflammation are followed by weeks, months, or even years of apparent inactivity. However, ERU is an auto-immune disease where the body’s own immune system may continue to attack eye tissue in between obvious episodes. These attacks produce signs such as squinting, tearing, “red eye,” a cloudy eye, swelling, and sensitivity to the sun.

What breeds does it affect?
There appears to be a genetic component to this syndrome, as Appaloosas are more likely to develop ERU. Warmbloods and draft breeds also seem to be at slightly higher risk than the general equine population.

What can be done to prevent it?
Leptospirosis, a bacterial infection, has been associated with ERU, so efforts to reduce a horse’s exposure to the disease (such as avoiding water from lakes, ponds, rivers, and streams) may aid in prevention. Otherwise, close observation for any abnormality of the eyes and prompt examination, diagnosis, and treatment by a veterinarian may help control inflammation before permanent damage occurs.

What are treatment options?
Aggressive anti-inflammatory medications, both steroidal and non-steroidal, are generally prescribed topically (directly in the eye) as well as systemically (injected or fed orally) to limit eye tissue damage. Dilating agents such as atropine may also be used to relieve pain and prevent complications. If an underlying cause for the condition can be found during the physical and ophthalmological examinations, then this would be specifically treated too, perhaps with antibiotics. Consistent treatment and follow-up are important because each attack causes more permanent damage, eventually leading to blindness and perhaps even removal of a severely affected and painful eye, called enucleation. Some horses remain on anti-inflammatory medication (like aspirin) for life, in an attempt to prevent flare-ups of the disease. Fly masks can be a helpful management tool during and between attacks to protect the eyes.

Is a crossbred horse less likely to contract it?
Since experts aren’t exactly sure what causes Appaloosas to be at a higher risk for developing ERU, it’s not clear if being full-bred or part-bred makes a difference.

Lydia F. Gray, DVM, MA SmartPak Staff Veterinarian and Medical Director Dr. Lydia Gray has earned a Bachelor of Science in agriculture, a Doctor of Veterinary Medicine (DVM), and a Master of Arts focusing on interpersonal and organizational communication. After “retiring” from private practice, she put her experience and education to work as the American Association of Equine Practitioner’s first-ever Director of Owner Education. Dr. Gray continues to provide health and nutrition information to horse owners through her position at SmartPak, through publication in more than a dozen general and trade publications, and through presentations around the country. She is the very proud owner of a Trakehner named Newman that she actively competes with in dressage and combined driving. In addition to memberships in the USDF and USEF, Dr. Gray is also a member of the Illinois Dressage and Combined Training Association (IDCTA). She is a USDF “L” Program Graduate and is currently working on her Bronze Medal. Find Dr. Gray on Google+

Posted in Ask the Vet, Diseases and Conditions

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3 comments on “Moon Blindness
  1. Muffie Harvey says:

    I am desperatley seeking an equine eye Dr for my Appaloosq gelding , it appears he has cataracts. Can you guide me to anyone…..we live in central Vt.

    Thank you in advance…..”Joe” and I work hard to Ride for The Cure and raise ,obey for breast cancer research. We are a one woman -one horse team that ride the length of Vermont…our trip covers about 200 miles…..we did not do the ride this year due to his eye issues. Other than this he has many years left in him to touch people’s lives……any help for my Joe would be greatly appreciated.

    Many thanks,

    Muffie & “Joe”

  2. Shawna says:

    My appaloosa “Toby” has ERU. He has had 2 bouts in a years time. I use a fly mask year round. I have also ordered a sun visor from Nag horse ranch. He has accepted both without any reservations. He has some vision loss but we still trail ride. I live in WV and my vet diagnosed this for me. When I called a specialist near me she stated that any vet should be able to diagnose this disease.

  3. Cathy says:

    I had a Standardbred who developed moon blindness, so it does happened other breeds too.

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