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Home:Equine Diseases: Recurrent Uveitis

Equine Diseases



Synonyms: Moon Blindness, Periodic Ophthalmic, Chronic intraocular inflammation


Equine Recurrent Uveitis (ERU) is an affliction of the horse's eye that can be caused by many different things - bacteria, virus, parasites, or trauma.
Equine Uveitis is often diagnosed as something far less serious and valuable treatment time is lost. If treated aggressively from the onset, there is higher chance of saving sight in one or both eyes. Unfortunately, even with very aggressive treatment, some eyes cannot be saved, but in other cases the disease can be halted or at least slowed down.
Every attack of equine uveitis damages the sight further, so the quicker the treatment the higher the chances are of saving the horses sight.


Equine Uveitis unfortunately is often misdiagnosed as something less severe or in some cases it is totally ignored. It is important that uveitis be diagnosed correctly and quickly because lack of or incorrect treatment can have serious consequences.
Equine recurrent uveitis is very painful to the horse.
The most common symptoms of equine moon blindness (uveitis) are:

• Puffy
• Watering eyes
• Photophobia
• Squinting
• Red blood vessels at the sides of the eye and in the lids
• Photophobic (very sensitive to light)
• White cloudiness
• Blue or green tint in the eye
• Pupil that is constricted when the horse is in the barn or a darkened stall. (A constricted pupil indicates that it is in spasm, and is very painful. Immediate treatment is needed to alleviate the spasm.)
Other less clear signs of equine uveitis may include:
• Head shaking
• Runny nose
• White spots or bleeding in the eye
• Pus
• Loss of balance
• Tripping
• Rubbing the eye.

*In some cases if you look across the surface of the eye you may even see ulcers. They look like little declivities, but usually you will need to stain the eye to see them and the untrained eye can still miss them.


As aforementioned, the causes of equine uveitis come from bacterial, viral, parasitic, and traumatic sources. Allergies have also been linked to causing equine Uveitis.


Leptospriosis is the most common bacterial infection causing irreversible damage for the host animal e.g. Abortion, still birth, decreased milk production and even death.
Streptomycin and penicillin are used to treat leptospirosis.


The major viral infections linked to equine uveitis are respiratory equine herpesvirus and influenza virus.


The most common parasite connected with equine uveitis is onchocerca. The adult lives in the connective tissue of the horse's neck.

The most common signs of it are:

• sores aligning the midline of the horse's stomach
• base of the mane and withers
• uveitis in the eye

Equine Uveitis occurs when there are large quantities of dead microfilaria in the eye. Microfilaria are part of the biting midge that travels through the bloodstream. When dead microfilaria give off copious amounts of antigens which cause inflammation in the eye and ironically once the horse has been wormed, the disease will flare up again. Therefore onchocerca can sometimes first be identified by the onset of symptoms following worming with certain drugs.
Administering bute or banamine can control the inflammation in the eye if given a few days before and after worming.
Toxoplasma gondii is also another parasite known to cause uveitis. The cat is the host but horses can become infected through direct contact with infected cat faeces will cause contamination.

Trauma to the eye causes equine uveitis and cataracts.
If penetrated by a plant foreign body a corneal ulcer or fungal infection may develop. These can be treated. Cataracts can be removed by surgery but it is risky due to the eye of the horse being a lot larger than that of the human eye. It will take longer to heal and cataract surgery can pose many post-operative problems. This in itself can cause equine uveitis to flare up again.

Research has been carried out and one study showed that during the month of May and the month of October the onset of equine uveitis was the highest. This would indicate that allergies should be considered as a possible cause. Pollen type allergies as well as combination of seasonal vaccines should be examined as a preventative measure. So whilst it is not conclusive, allergies should be given some thought as being a cause of equine Uveitis in horses.


Atropine dilates the eyes causing the spasm in the iris to stop. This alleviates a lot of discomfort and pain.
Steroids and antibiotics would follow. Which one is used is dependent on whether the eye is ulcerated or not.
Bute, banamine or aspirin are used as anti-inflammatory agents.
When it has been treated there can be repeat episodes. Internal or external circumstance can be to blame. The episodes will continue to occur and each time it will last a little longer. After the original episode has been successfully treated, the inflammation and signs will disappear and the eye may appear to be normal or almost normal. At sometime in the future, if it is equine recurrent uveitis, a set of circumstances will cause the eye to have another episode. The best treatment is to recognise the signs from previous episodes and treat immediately.