What is uveitis and what causes it?
Uveitis means inflammation of the uveal tract of the eye. The uveal tract consists of the iris, the ciliary body and the choroid. These are the vascular (blood vessel) and pigmented structures of the eye.
Uveitis can be caused by
- Ocular trauma
- Systemic bacterial or viral infection
- Leaking of lens proteins from a cataract
- Ocular tumors
- Immune-mediated disease
What is Equine Recurrent Uveitis?
Equine Recurrent Uveitis (ERU), as its name implies, is a chronic, recurrent form of uveitis and is also known as
- “Moon blindness”
- Periodic ophthalmia
We are unsure exactly what causes some horses to develop a recurrent form of uveitis and others to only have a single episode. If not treated aggressively, the repetitive bouts of inflammation can cause scarring and permanent damage to the eye, including blindness. ERU is one of the most common causes of blindness in the horse. The recurrent episodes of inflammation can occur in one or both eyes. It is impossible to predict when an episode will recur, however some owners have reported seasonal patterns or increased likelihood of an episode around vaccination or deworming. Your veterinarian can help you tailor your preventative care program to help decrease the potential for a flare up.
Signs of uveitis:
Common signs of uveitis you may observe include:
- Redness and swelling of the eye
- Squinting or sensitivity to light
- Cloudiness or blue-ish haze to the cornea
These are the most common signs that owners usually notice in the beginning stages of the disease. Signs of uveitis can be very similar to the signs of other eye problems. Therefore it is very important to consult with your veterinarian whenever you have concerns about your horse’s eyes. Often it is necessary to sedate the horse and numb the eyelids in order for the veterinarian to fully examine the eye. Although the signs may be similar, treatment for uveitis is drastically different than treatment for other eye problems, such as corneal ulceration.
Your vet can diagnose uveitis based on the findings of a complete ophthalmic examination. If two or more episodes of uveitis are documented, then a diagnosis of ERU is made. It is possible to observe some of the chronic changes that have occurred when an eye is not actively inflamed. This is why a full ophthalmic exam is an important part of a pre-purchase examination.
Treatment for a single bout of uveitis:
Uveitis is treated with a combination of systemic and topical anti-inflammatory medications. Banamine and Bute are non-steroidal anti-inflammatory drugs that also have pain relieving properties. Banamine is considered more effective than Bute and aspirin. In the case of uveitis, a topical steroid ointment or solution usually combined with an antibiotic is also used. Steroids are more potent anti-inflammatory drugs and topical application allows us to get high concentrations of the medication into the eye. The use of topical steroids is contraindicated in the presence of a corneal ulcer. Make sure your vet has ruled out corneal ulceration before using a topical steroid. A medication called atropine is also applied topically. This medication causes the muscles of the pupil to relax, thereby dilating the pupil. It is also important to protect your horse’s eyes from light, irritants or trauma by keeping him/her is a dimly lit stall or arena and using a fly mask. Additionally, be careful not to rub your own eye after application of the atropine. It will cause unpleasant but short-term dilation of your own pupil. If you have had a complete exam by a human ophthalmologist you know what this feels like.
Treatment for Recurrent Uveitis:
Active bouts of inflammation in patients with ERU are treated the same way as described above to minimize pain and inflammation and permanent damage to the eye. Daily administration of Bute and other supplements such as MSM have shown limited efficacy in preventing or decreasing the severity of recurrent episodes. Some veterinary ophthalmologists advocate maintenance on daily aspirin. It is unclear why, but there is anecdotal evidence that it may slow recurrence. Surgical implantation of a device that delivers a powerful immunosuppressive drug called cyclosporine A over a 3-4 year period has shown to be effective in decreasing the duration and severity of inflammation and tissue damage in the eye. However, horses with active inflammation that cannot be controlled with NSAIDs and topical steroids are not likely to respond to treatment with cyclosporine A.
Extreme vigilance for any subtle signs of a recurrent bout is essential. Contact your veterinarian immediately if you have concerns that an episode is starting.