Equine recurrent uveitis (ERU) is unfortunately a common condition in horses, impacting up to 7% of farms with at least one horse affected. ERU is considered one of the most common causes of blindness in the horse and seems to impact many breeds, but with certain predilections to the Appaloosa and Paint breeds. The condition is very complex with much to be learned and understood in terms of pathophysiology, but treatment options can offer some help in managment and preservation of vision.
The eye is a complex organ composed of the anterior (front) chamber, posterior (rear) chamber, and other vital structures including the cornea (clear front part of the eye), the iris and the retina which helps to process signals for vision. All of these structures need to be fully functiona and clear by nature in order for vision to be intact. Equine recurrent uveitis can impact potentially all of these sructures, leading not only to pain but potential loss of vision.
The exact cause of ERU is not completely understood or isolated in every case. It is believed to be an autoimmune type of condition, in which the immune system essenially becomes over-reactive, physically attacking the various tisses of the eye. In terms of potential causes of uveitis in the horse, there are numerous including trauma, various bacterial and viral infections, parasitic infections and sources of systemic toxemia (endotoxemia) or even cancer. The bottom line connector between these causes is a disruption of normal immune function to one degree or another, specifically involving a type of white blood cell called the lymphocyte.
In some cases, concern has been raised as to the connection with a bacteria called Leptospirosis, which is generally contracted through contaminated water sources, courtesy of livestock or deer. In most cases of active Leptospiral infections in horses, the animal is clinically sick with fever, malaise, loss of appetite and jaundice. Horses demonstrate a marked rise in antibody levels within a few days and the active immune response usually quickly eliminates the organism, but in some cases it can localize in the urinary tract and components of the eye, which may trigger ongoing inflammatory attacks associated with ERU.
Pathology and Diagnosis:
The potential causes of ERU are numerous, but the underlying problem is ongoing inflammation associated with immune dysfucntion. The constant release of various inflammatory proteins and heightened activity of specific immune cells called T-Helper cells, leads not only to pain, but ongoing tissue destruction, through the ongoing release of pro-inflammatory proteins or cytokines. When presented with a horse with any active eye condition, it is important to rule out other potential causes or problems including; uveitis, corneal lesions or ulcers, trauma, foreign bodies, infections, neoplasia or cancer. Many of these conditions can present with similar clinical signs, but treatment options are different.
Presenting signs of ERU depend really on the stage in which the horse is presented to the veterinarian. Uveitis is a common condition in the horse, but technically, in order to be diagnosed with ERU, they must have experienced 2 or more recurrent episodes of ongoing inflammation or ‘flare-ups”.
Possible presenting clinical signs of ERU include obvious pain, squinting of the eye (blepharospasm), constricted pupil (miosis), increased blood vessels on the cornea (neovascularization), increased redness to the conjunctiva or white part of the eye, increased tearing (lacrimation) in some cases, increased sensitivity to light (photophobia) and loss of corneal transparency (corneal edema), which implies a cloudiness or haze to the cornea. Dependent on the severity of the clinical signs, vision may be impaired to one degree or another. In many cases, only one eye is involved initially, while in others both may be affected.
In the picture directly below, we can see that the cornea is cloudy in appearance, the conjunctiva or white part of the eye has increased blood vessels and redness and there are some new blood vessels apparent on the cornea itself.
What we have to understand is the the disease impacts the entire eye and with time, other structures can become involved. One such structure is the iris, which forms the pupil. Initially, the iris contracts or becomes smaller in response to pain. Over time, if the iris is constantly closed, it can actually become stuck to surrounding structures, which then impacts its ability to open and close. This is called ‘synechia’ and is a common finding in more end-stage ERU cases. In other situations, the iris itself can degrade or degenerate, which also impacts vision in the long term. Here are two more images, demonstrating different changes in the iris. In the image to the left, the iris is actually stuck to itself on one end, while there is also corneal cloudiness and neovascularization. The image to the right demonstrates iris degeneration and possible cataract formation.
Clinical Treatment & Management:
The goal with any therapy in cases of ERU is to control pain, reduce inflammation, slow progression of disease and maintain vision. In most instances pain and inflammation are controlled with the use of topical corticosteroid medications and/or injectable or oral non-steroidal pain medications. Often, the use of these therapies help to reduce pain in early stages, helping to reduce clinical signs, but do little to prevent future flare ups. With each subsequent flare up, more tissue damage is done and vision loss potentialy occurs.
One somewhat new approach to controlling future flare ups is the use of a medication called Cyclosporine in a surgical implant. Cyclosporine can be used topically as a medication, but requires frequent administration. It works specifically by reducing the immune response, by impacting the lymphocyte. In the surgical approach, an implant containing Cyclosporine is placed outside of the eye under the conjunctiva, which then releases the medication over time, potentially helping to reduce flare ups. In clinical studies, the approach has proven useful, but appears to be limited to early stage disease. In my experience as a vet, we have had mixed results with patients coming back and having future flare ups despite the implantation.
Vaccination against leptospirosis is yet another topic and may prove valuable in farms that are predisposed to infection from this organism. In some studies, vaccination has decreased the incidence of disease on some farms. Treatment and testing for Leptospirosis is generally not performed, unless there is active disease, as likely the inflammatory response is isolated to specific regions and antibiotic therapy may not be of value.
I do believe that the use of targeted, inflammation reducing herbs including Curcumin and Boswellia, have proven very beneficial in managing many cases of ERU, especially those that have continued to relapse despite currentl therapies. Curcumin and Boswellia, amongst other herbs, impact the inflammatory pathway by reducing pro-inflammatory proteins including interleukins, which may play a role in cellular signaling of the immune response and MMP’s, which may be involved in tissue destruction. Other anti-inflammatory herbs including Dandelion, Marshmallow and even Aloe have also proven beneficial in many cases, and also impact digestive health, which is one of the primary sources of the immune response. I have also found the use of mushroom derived beta-glucans to be especially beneficial, when used along side of herbal anti-inflammatories, as they help to modulate or calm down the overactive immune response. Spirulina blue green algae has also proven to be of value, not only due to providing vital nutrients for ocular health, but the algae helps to reduce inflammation and acts as a natural antioxidant.
The overall bottom line point with the use of ‘alternative’ therapies is that in reality, they are foods, which impact health on a postive note, helping to rebalance pathways that are out of control. Situations like ERU are much like other conditions in that the inflammatory response is systemic and ongoing, often contributing to other conditions. If we use foods or herbs that impact these pathways, it is in my opinion that we can dramatically impact these clinical problems. Inflammation is a complex pathway, but herbs allow us many approaches or means of controlling it from direct regulation of inflammatory pathways to provision of nutrients and antioxidants, all of which help to improve cellular health.
We have found the best results clinically in these patients by combining our Cur-OST EQ Total Support with the EQ Immune & Repair formulas. In some cases, the inflammatory component is very strong and needs a more critical approach to help manage it, in which case we will start with our Pure EQ formula due to containing high levels of Curcumin. By doing this, we not only supply multiple herbs to combat inflammation including potent levels of patented BCM-95® Curcumin, but also Boswellia, Dandelion and marshmallow. The EQ Immune & Repair provides a nice blend of multiple mushroom beta-glucans and amino acids that effectively modulate the immune response, helping to produce some nice results and reduce flare ups.
Long Term Prognosis:
In some studies, it has been shown that over 50% of horses impacted by ERU will go blind in one or both eyes. The end stage disease results often in full blindness, due to degeneration of tissue and cataract formation. Pain is the ultimate concern, at least in my opinion, with all of these cases. In those situations in which pain cannot be controlled, removal or enucleation of the eye is often warranted.
I do find that many of these cases can be quite challenging to manage for the long term despite our approach. I also believe that the use of various herbal therapies, mentioned above, can prove very beneficial and in our hands have helped to dramatically reduce future flare ups and improve quality of life for these patients.
For more detailed information, please fee free to contact me.
Tom Schell, D.V.M.
Nouvelle Research, Inc.
Gilger, B. Equine Opthalmology 2nd Edition, Saunders, 2011, 317-349.
Photos courtesy of Ohio State College of Veterinary Medicine, Opthalmology Dept.