Equine Recurrent Uveitis

ERU (also commonly known as Moon Blindness or periodic ophthalmia) is extremely common in Appaloosas. Nakai was diagnosed officially with ERU back in 2013. While there is a wealth of information available online and through studies, ERU is still a confusing disease. The causes can be unclear, varies from horse to horse, and as an owner of an afflicted horse I occasionally end up with more questions than answers when I research.

Equine Recurrent Uveitis is label as an immune mediated disease. The body’s immune system attacks the eye tissue. The exact cause is largely unknown, and there is currently no cure. Horse owners rely on an arsenal of treatment options to keep the disease under control.

Nakai’s first flare up was in early November 2012. He came down suddenly with a 104 degree fever, was lethargic, not eating, and generally unhappy and sick. He was put on banamine and oxytet. A couple hours later he developed an swollen, teary eye – a uveitis flare up. He was placed on doxycycline, atropine, and steroids for his eye. And thus: my rough introduction into the world of Equine Recurrent Uveitis.

Signs of ERU can be as simple as excessive eye tearing. Or, it more often appears as the signature signs: puffy, weeping eyes that are clamped shut and painful. There is often squinting, and the red blood vessels around the eye are long and angry looking. Another huge sign is a constricted pupil. Constricted pupils are very painful, and relief in a dark stall is necessary. My vet explained in laymen’s terms that it feels like a huge cramp in their eye. Controlling the constriction is critical, and Atropine is often used to dilate the pupil while on a steroid regimen.  If the pupil is not dilated, scar tissue can build up and prevent the pupil from being able to widen on its own even after the flare up has subsided. Other signs of ERU can be head shaking, white spots or uclers in the eye, eye rubbing, loss of balance, spookiness, and avoidance of sunshine. Bottom line – if their eye looks ouchy, or something just isn’t quite right, call your vet immediately.

There are actually three types of ERU: classic, insidious, and posterior.

Classic is the most common. It is also known as anterior and is the usual combination of pain and inflammation that is then followed by an inactive period before becoming active again. Repeated bouts of classic and insidious ERU can lead to blindness and glaucoma. With insidious, a low grade inflammation continues after the active phase and continues to target and damage the internal structures. The horse doesn’t always show outward signs of pain. By the time it is realized the damage is too great (and the horse often blind). Finally, in posterior the inflammation is behind the lens. Vitreal opacities (floaters) and retinal detachment are associated with posterior ERU.

I have no idea if Nakai had any previous flare ups before he came to me, but at the time of his first known flare up he was about 21 years old. I lean toward his illness causing his initial flare up. ERU causes seem to be anything and everything – from trauma, environmental factors, infections (leptospirosis), and possible genetics. Once ERU is established it seems triggers are everywhere – from the too bright sun, flies irritating the eye, debris in the eye (such as dust, hay particles, etc), blowing sand or snow, strong wind – anything that irritates the eye has a possibility to produce a flare up. Routine vaccinations, stress, and UV rays can also be triggers.

You need to take the individual horse into consideration, but until you narrow down the triggers it can feel like an endless mine field. If possible, keep a log of flare ups and the possible triggers associated. This can help you and your vet identify the main triggers and create a plan to combat them.

Nakai’s specific triggers seem to be fly irritation and debris (such as dirt or bits of hay in his eye). He also loves to rub, so that can also lead to irritation and a flare up. I struggled endlessly to find a fly mask that fit well, stayed away from his eyes, did not rub, AND would stay on my Houdini horse. Nakai is on a careful vaccination schedule, and he wears the Equivizor fly mask from Protective Pet Solutions the moment I see bugs. From late spring to early fall, he wears his mask 24/7 unless we are riding.

Sometimes you cannot anticipate flare ups. Last summer, Nakai trotted into a tree in his pasture. He was flipping his head around, showing off and not wanting to be caught, and whacked his head (and his bad eye) solidly on the tree. 10 days later, he had a flare up. As much as we try to eliminate potential threats, occasionally all you can do is sigh, grab the medicine, and ask them to please make better choices.

As mentioned earlier, currently there is no cure for ERU. Flare ups are best managed immediately and aggressively with medicine (or whatever treatment your vet prescribes). You may be doing steroid drops 3-4 times a day on top of Atropine, a dark stall, etc. Once medical treatment no longer provides relief, surgical options are available (such as a cyclosporine device implant that releases a determined dosage of medication directly into the eye). Some owners choose to remove the eye completely.

Unfortunately, the majority of ERU horses go blind in the affected eye.

This is what happened to Nakai. He has scar tissue built up and a small cataract that is forming. He is now completely blind in his right eye. This doesn’t mean he is safe, however; he is still at risk for flare ups. For this reason, he is only a steady regimen of MSM, 1/2 tablet of bute daily, his ERU mask when applicable, an extended vaccination schedule, and other safety precautions to reduce his triggers.

A blind eye is a whole new territory – his eye will continue to shrink, although I am not sure how quickly it will do so. As it shrinks, items that were previously held in place by a healthy eyeball (such as his conjunctiva and third eyelid) may move and shift. Similarly, he may appear more weepy or tearing more often because the tear duct tract has shifted for the same reason. It was quite the scare to see his conjunctiva protruding more than usual. Always confirm with your vet on anything eye related.