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Moon Blindness

16 August 2011 2 Comments

Moon Blindness
We asked horse training expert Dr. Jessica Jahiel, whose teaching goal is to develop balanced, willing, forward horses and thoughtful riders. More about Dr.Jahiel

Dear Jessica:
My horse’s foal (who’s now grown up) was seven when he got moon blindness in both eyes and had to be put down. My horse is 19 now and had Smoky, the foal, when she was 10. Is there any sort of reverse-genetic thing that might cause her to get moon blindness? And also, what exactly is moon blindness and can it be prevented?


Hi Cindal!
First, if you look for information on moon-blindness, you’ll find much more of it if you look under “uveitis”, “recurrent uveitis”, and “periodic opthalmia”. “Moon-blindness” is just a name for the disease. It’s a name that was popular when people believed that the regularly-occurring acute episodes were connected with the cycle of the moon.
Whatever name you use for it, uveitis is the most common cause of blindness in horses. It’s an eye disease with a number of different known causes including direct trauma, bacteria, viruses, and parasites – even allergies are suspected to be involved in some cases.
The very first thing you need to do if you suspect that your horse has uveitis – or indeed if your horse shows signs of any eye problem at all – is to CALL YOUR VET.
If you’re wondering how to notice an eye problem, it’s not very complicated. If you know what your horse’s eyes look like when they are normal, and you look at them daily, you’ll notice very quickly if anything has changed. If your horse has a red or swollen or cloudy eye, if you come out and find your horse squinting or avoiding light, don’t assume that it’s “just dust” or “just a windy day” or that the problem will disappear if you ignore it. Eye problems are too serious and too dangerous, and the equine eye is far too delicate, to take a chance.
Don’t try to treat it yourself, and don’t wait to see whether the problem will go away. Both of these decisions are bad. Ask your vet to come out and look at the horse, or take the horse to the vet. Get a professional diagnosis as soon as you can, don’t wait! Time is important; the sooner the condition is diagnosed, and the sooner the vet (and you) can begin an aggressive treatment, the greater your chance of saving the sight in at least one of your horse’s eyes. In some cases, the disease progresses too quickly for the horse’s sight to be saved; in other cases, the vet is called too late. If you get a diagnosis as soon as you see the first signs of eye trouble, it’s sometimes possible to stop the disease, and it’s often possible to slow it down.
You’re going to be involved in your horse’s treatment. When the vet has diagnosed uveitis and checked the eye for a corneal ulcer, short-term medical treatment will begin. This will usually involve several topical medications. Most vets will prescribe atropine (this dilates the pupil) and an antibiotic or steroid. The determination to use a steroid, and the choice of an antibiotic, must be made by the veterinarian based on his diagnosis of your horse’s eye. The wrong antibiotic will be useless; if your horse has an ulcerated cornea, the use of a steroid in that eye can “melt” the cornea and blind the horse.
Your vet will show you how to apply the various drops and ointments, and will probably also prescribe a general anti-inflammatory drug (bute and aspirin are commonly used). You may need to administer treatment two, three, or four times a day.
There’s a reason this disease is called “recurrent” opthalmia. Even if you and your vet deal successfully with the initial episode, and your horse’s eye seems to be normal again, you can’t ever relax and stop watching for signs of trouble. At some point, there will be another episode; if you deal successfully with this one, there will still be another one later. Each episode will cause a little more damage and take away a little more of the horse’s sight. Typically, each episode will last a little longer and be a little more difficult to deal with than the previous one.
In the long term, you’ll probably use topical medications only during acute episodes; the rest of the time, you’ll be dealing with a maintenance regimen that may include daily aspirin or bute, and in some cases might even include antihistamines. Fly masks can help keep dust and debris out of a horse’s eyes, and can also cut down on the amount of ultra-violet light coming into the eye. If you need to block all light from one eye, you can sew a soft pad into the flymask.
I also using dietary supplements to help build up the horse.
A horse with untreated uveitis can be a danger to himself and to the others
– horses and humans – around him. As his eyesight becomes worse and worse, he will be more likely to bump into things, and more likely to react suddenly if he is surprised by a human coming up to him without speaking to him first. If his human caretakers don’t realize that he is losing his eyesight, they won’t handle him correctly, and someone will get hurt.
Another reason that a horse with untreated uveitis can be dangerous is that he won’t be dealing just with a loss of eyesight – he’s likely to be in great pain. A horse that can’t see you approach may startle when you touch him; a horse that can’t see you AND is in acute pain may kick out. If your horse is showing signs of pain – looking distracted or preoccupied, acting less interested in people or food, acting less friendly – don’t hesitate to call the vet right away.
Don’t assume that an eye must be badly swollen or dripping pus to be painful. Pay attention to ALL of your horse’s behavior – sudden clumsiness is often the result of a vision problem. If your horse is in pain and you suspect an episode of uveitis, but don’t see any swelling or redness in the eye, take him into the barn, make it as dark as possible, and look at his eyes. If you find a constricted pupil (it should dilate in a dark barn), then call the vet immediately, because this horse is in severe pain and needs immediate treatment.
As far as your own mare is concerned, there is really no way to predict whether she will or won’t get uveitis at some point. All you can do is have your vet inspect her eyes closely and determine whether she has had any episodes before now. Then, like all horse owners, you’ll just have to watch and wait. There’s no age at which a horse becomes immune – and many horses do seem to develop uveitis in their later years.
There’s no way that the disease afflicting a seven-year-old horse will somehow jump backward, genetically speaking, and affect the parents of that horse. It IS possible that a tendency to get uveitis may be heritable. Uveitis can occur in horses of any breed, but it does seem that Appaloosas are particularly vulnerable. If Smoky was the product of your mare and an
Appaloosa stallion, it’s possible that his Appaloosa heritage might have increased his vulnerability to the disease.
Your best bet with your mare – or any other horse – is to keep all of your horses as healthy and happy as possible. Anything that promotes inflammation in the eye can trigger an episode of uveitis. Anything you can do to build up a horse’s immune system may help the horse avoid any number of illnesses and diseases, and it’s reasonable to think that keeping a horse’s immune system strong might help protect it from developing uveitis.
But it’s still a disease with a lot of “unknowns”. If you even suspect that your horse may be developing uveitis, plan ahead to eventual blindness, and change your horse management practices and training and riding practices accordingly. The changes can’t hurt – and if your horse does become blind, they can make the difference between a walking disaster and a successfully managed horse.
If the worst happens and your horse does develop uveitis and eventually becomes blind, you may still be able to continue riding her. There are some questions and detailed answers about that in the HORSE-SENSE archives.

Sincerely, Jessica


  • Tab Kelly said:

    Our horse is 5 and she was diagnosed with Uveitis. Our vet said not to give her anything to “build her up”, but I want to. I want to help her. Can you give me some examples as to what I should give her to make her healthy as possible? She is also on asprine daily for the rest of her life. Is that alright or should we be doing every other day? I am very scared for her. She is trained well but a lot of visual ques…We need to change that but I believe we can handle her. My daughter is very patient with her and I think what ever happens she can handle her. It’s just a very sad thing.
    Thank you…

  • June Black said:

    I have a 35 year old mare with moon blindness in one eye and now the other one is developing very cloudy should I try and treat her or when is the time to put her down. Thank you

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