Equine Recurrent Uveitis
Other Names: Moonblindness, panophthalmitis, iridiocyclitis, periodic ophthalmia
Equine recurrent uveitis is a painful inflammatory response involving the gel (uvea) inside of the eye. This inflammatory response can occur as a primary problem, particularly in certain breeds, or as a consequence of other infection or injury to the eye. Uveitis may occur as a low-grade insidious disease or have a sudden onset after a specific event. Trauma, severe ulcers and severe infections can all cause uveitis. In many cases the recurrent uveitis may not be evident until long after the original issue is resolved.
Uveitis can occur as a result of infections from rickettsial bacteria, Leptospira spp., and Borrelia burgdorferi (the agent that causes Lyme disease). Leptospira bacteria is shed in urine from infected mammals such as rodents and deer. Most horses become infected with Leptospira through contact with contaminated water or feed sources. In horses, Leptospira infection often clears the rest of the body on its own, but may linger in the eye. Borrelia burgdorferi is carried by ticks and is quickly becoming more prevalent in our area.
Certain breeds have a genetic predisposition to uveitis. Uveitis is diagnosed more frequently in Appaloosas, Rocky Mountain, and Paso Fino horses. Appaloosas have a particularly tricky and severe type of uveitis that is related to their mottled skin color, known as pigmentary uveitis. Appaloosas showing signs of pigmentary uveitis may show very little sign of pain and go unnoticed until the disease has progressed to blindness.
Regardless of the original cause, uveitis progresses to an autoimmune disorder. In a normal state, the immune system perceives the eye as a separate compartment from the rest of the body. Anything that disrupts this relationship can result in uveitis. Once the immune system has been triggered, it will periodically attempt to “attack” the eye, resulting in Equine Recurrent Uveitis.
Early signs of uveitis are primarily related to pain and may be overlooked as an “allergy” or “cold” in the eye. Signs of eye pain include squinting, excessive tearing, redness and swelling around the eyelids. Tearing is usually clear to cloudy and creates a wet streak down the face. More obvious signs of uveitis include a blue, silver or gray hue to the eye. In some cases, the eye may appear larger than the normal eye. Vision may be temporarily decreased or lost, but may be recovered with appropriate treatment. Often, horses suffering from acute flare-ups of uveitis will be nervous, “jumpy,” or exhibit behavior problems related to pain from the eye. Imagine having a throbbing migraine headache with no relief. Uveitis usually occurs in one eye at a time. However, it is possible for it occur in both eyes, either alternating or in both eyes simultaneously.
It is important to note that this condition is naturally cyclic. Often owners recall that the horse may have expressed eye pain or discharge in prior instances that appeared to resolve. Over time, the severity of uveitis flare-ups will increase while the intervals of flare-ups will decrease. This results in more severe and more frequent flare-ups until the eye is in a continued state of inflammation and pain. With each recurring flare-up of uveitis, the eye will sustain more permanent damage, decreasing the overall longevity of a functioning and visible eye.
A physical exam including a complete ophthalmic evaluation is the most valuable tool for diagnosing uveitis. Many flare-ups can be complicated with corneal ulceration or glaucoma. It is important to know if an ulcer or glaucoma is present, as it will affect the treatment protocol. In addition, blood samples are often collected to test for complications of Leptospira or Borrelia infections. Results of Leptospira testing will also help determine a prognosis and likelihood of the opposite eye becoming affected.
Acute Flare-up: During the acute flare-ups, treatment is aimed at aggressively reducing pain and inflammation, and treating any ulcers or glaucoma that were noted during the exam. Treatment consists of topical medications (steroids, NSAIDS, antibiotics, and atropine for pain) and systemic NSAIDS. The length of treatment for each flare-up will depend on how long it has been going on. The longer the eye has been flared the longer it will take to treat.
Long-Term Management: There is NO CURE for this disease and it will continue to progress over time. However, many horses may live comfortably and continue successful careers for many years. Others may fail to respond to even aggressive therapy. It is extremely difficult to predict how quickly the disease will progress.
CAUTION: Eye medications with steroids (prednisolone, dexamethasone, or hydrocortisone) can be harmful and CATASTROPHIC in the presence of an ulcer on the eye. Do not treat the eye with steroids without a prior consult to ensure that an ulcer is not present.
Some horses will require regular maintenance treatment while some will only require treatment of flare-ups. As an alternative to topical treatment a long-term medicated implant can be surgically placed in the “white” of the eye. This implant will release medication slowly over time. At this time, we do not offer this procedure. However, we are happy to refer to a board certified veterinary ophthalmologist. The implant is not lifelong and will need replaced every few years.
Unfortunately, in some cases, uveitis will not respond to treatment. Removal of the eye (enucleation) should be considered in cases with intractable pain or that are blind. Once the eye is non-visual, it serves only as a source of pain. Enucleated horses function very well in many disciplines.
Causes of Flare-Ups
Patients with uveitis should be monitored carefully during any illness or when vaccinations are given. Any stimulation of the immune system may trigger a flare-up. This is not a reason to skip vaccines. In fact, vaccination and prevention are even more important in uveitis patients. However, a pre-treatment may be given to reduce the chance of a flare-up from vaccination.
Recognizing Early Signs of Flare-Up
One of the most important aspects of controlling this disease is recognizing early signs of flare-up and seeking treatment immediately. Any sign of eye pain, excessive tearing, red eyelids, swelling or squinting should be taken seriously. Treating immediately shortens the treatment time and reduces damage caused by each episode of flare. Owners are encouraged to keep some medications available for sudden episodes.
Genetic Testing: Unfortunately, there is currently no genetic testing available to predict this disease in horses.
Pre-Purchase: It is impossible to guarantee that a horse will not develop uveitis and very difficult to detect when the eye is “quiet”. However, there are a few signs that veterinarians look for during a pre-purchase exam to help determine whether uveitis has been present in the past.
Vaccination: A vaccine is available for prevention of uveitis caused by Leptospira pomona. Unfortunately, it only protects against one type of Lepto (there are at least 6 types) and offers no protection against other causes of uveitis. In our practice, we generally use this vaccine in AT-RISK cases, such as horses with eye abnormalities or farms where Lepto has been identified as a problem before.