What are Moon Blindness?
Moon blindness, or iridocyclitis, is an immune-mediated eye disease which is painful to horses. It is commonly referred to as equine recurrent uveitis (ERU). This is a very common eye disease in horses and can lead to blindness. The name moon blindness refers to the fact that the disease goes through stages of waxing and waning. This disease has characteristics of intense bouts of pain and inflammation, which may fade away for a few weeks or months, leaving the horse with no apparent symptoms. However, since this is an immune-mediated disease, the horse’s cells may continue fighting and attacking the tissue of the eye and between flare-ups. This may result in tearing, squinting, and other symptoms, which may be painful.
The inflammation tends to occur within the eye and negatively affects the uveal tract. This thin layer of tissue is between the cornea and the retina of the eye. The iris is considered to be the front part of the uveal tract, or the anterior part. The posterior portion, or back part, is comprised of the choroid and stroma. Moon blindness can affect both of the horse’s eyes or just one and any horse can become affected by this disease. There are some breeds which tend to be more at risk than others.
Moon blindness in horses is a disease of the eye which is immune-mediated. It can occur in one or both eyes and can be painful. This eye disease is also known as equine recurrent uveitis, or ERU.
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Symptoms of Moon Blindness in Horses
If your horse has developed moon blindness, he will exhibit symptoms characteristic of the disease. Symptoms may go away for a while and then come back. Symptoms include:
- Pain in the eye
- Cloudiness in the eye
- Change of eye appearance
- Reddened eye
- Eyelid swelling
There are other diseases and conditions of the eyes that can affect horses. Ocular diseases and conditions are quite common in horses. Other eye conditions include:
- Corneal ulcers
- Squamous cell carcinoma
- Trauma to the eye
Causes of Moon Blindness in Horses
Moon blindness is still being researched as to the specific cause of the disorder. It is known that this disease is not contagious and cannot be passed from horse to horse. Causes of moon blindness may be:
- Possible exposure to Leptospira bacteria
Diagnosis of Moon Blindness in Horses
Horses that have moon blindness will have several bouts of active inflammation in the eye. If your horse is exhibiting any of the above symptoms, even if the symptoms come and go, make an appointment with your veterinarian.
Your veterinarian will begin by doing a complete physical examination on your horse. This will include blood work, a biochemistry profile, a complete eye exam, and any other tests that he feels are necessary to get a preliminary diagnosis. Your veterinarian may choose to test your horse for an infectious condition known as Leptospirosis.
There are a few differential diagnoses of this condition, and your veterinarian will perform tests to be sure your horse is not being affected by a corneal ulcer or an abscess. Typically, eye conditions that are common in horses have the same or similar symptoms to moon blindness, with the main difference being that moon blindness comes and goes for no apparent reason other than the immune-mediated response your horse’s system is having. If your horse has had trauma to the eye or an ulcer within the eye, once he has recovered he should have no recurrences. Moon blindness is very recurrent, and this is what gives the veterinarian a major clue in the diagnosis.
A very typical sign of this condition that the veterinarian will be looking for is the darkening of your horse’s iris. Horses with moon blindness tend to have a very dark iris, but without any damage or scarring within it. The area around the iris may look very rough and irregular. In severe cases, scar tissue may have developed upon the iris from the inflammation that has come and gone. The veterinarian will be sure to closely examine your companion’s iris to help him with a definitive diagnosis.
Treatment of Moon Blindness in Horses
If your horse has been diagnosed with recurrent uveitis or moon blindness, the treatment will focus on decreasing or minimizing the eye’s inflammation and managing the pain that comes from this condition. There is no cure for moon blindness, so the treatment will be focused on preventing this condition from affecting your horse again over time. Treatment methods may include:
In order to decrease any inflammation of your horse’s eye, your veterinarian may recommend specific medications tailored to your horse’s condition. These medications may include anti-inflammatories, both systemic and topical, immunosuppressive prescription drugs, and steroids. The type of medications and the time period he will need them will solely depend on the individuality of your companion’s condition.
Research is still being conducted on surgical treatments to treat horses with moon blindness. Any surgical procedure will be discussed with you in detail by your veterinarian. Surgery methods may only be conducted by ophthalmologists that are highly knowledgeable of this condition in horses, as well as modern, high-tech equipment.
Recovery of Moon Blindness in Horses
This condition is progressive, as is the eye damage. The veterinarian will need to take action and do the best he can with aggressive methods of treatment. Recovery depends on your horse and the severity of his moon blindness. The scarring in the eye can lead to glaucoma, cataracts, and other conditions, including blindness. Your veterinarian will communicate with you the prognosis of your horse and how treatment is progressing.
In terms of any type of topical application of anti-inflammatory medications, you may need to have assistance in applying these to the eye. Many horses have a difficult time with eye medications, and your veterinarian will give you options on how to properly administer the medication or he may be able to administer the medication for you.
There is much research still being done on moon blindness and immune-mediated disorders in horses. Your veterinarian will communicate with you any new methods of treatment that arise. He will work with you and monitor your horse’s recovery, or the slowing down of the inflammation. He will also give you advice on how to properly care for your horse in terms of lifestyle management, such as by using netting to protect his eyes.
Moon Blindness Questions and Advice from Veterinary Professionals
My 8 years old Clysdale mare which weight aprocimitly 1800 to 2000 pound, was diagnose with moon blindness this last summer, we did everything we could ,giving her aspirin and making her wear a ultra violet mask and also giving her drop from our vet, my question is why would she try to turn around in her stall all the time and will not eat her grain , she seem to have lost her appetite and also not want to turn to her left at all, could it be something else, this behaviour only started a few day ago,
her left eye is completely covered with a blue film, so we feel that she is blind in that eye , we are not sure if she see in her right eye and we can not get in her stall on the left, she will not move over,she will only listen to my husband voice ,would appreciate any help or advice that you could give us
Linda R Furlotte
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