Equine Recurrent Uveitis Discussed at Vet Ophthalmology Meeting

Equine recurrent uveitis, also called moon blindness, is the leading cause of vision loss in horses. Brian Gilger, DVM, MS, Dipl. ACVO, chief of the Ophthalmology service at North Carolina State University's College of Veterinary Medicine, covered the topic at the first AAEP Focus on Ophthalmology meeting in Raleigh, N.C., last month.

The condition typically affects a small percentage of the equine population (1-2%), but there is a much higher prevalence of this disease in Appaloosas (20-25%).

Equine recurrent uveitis (ERU) is currently classified in three main categories:

  • Classic form which is the most common and involves episodes of active inflammation followed by latent low inflammatory periods;
  • Insidious form involves a chronic, low-grade active inflammation that often leads to signs of ERU, and
  • Posterior type which primarily affects the deeper areas (posterior) of the eye; the posterior form of ERU is the least common type in America but is more frequently seen in Europe.

A number of causative agents have been linked with the development of ERU, including leptospirosis, onchocerciasis, Streptococcus equi (strangles), brucellosis, toxoplasmosis, equine herpesvirus-1 and -2, equine viral arteritis, parainfluenza type-3, generalized septicemia, endotoxemia, neoplasia (cancer), tooth root abscesses, and even trauma.

Diagnosis is often initially based on clinical signs including blinking or closing the eye, corneal edema (which often appears as a bluish tint to the cornea), possible cataract formation, aqueous flare (small "floaters" in the front chamber of the eye), epiphora (watery eye), and even swelling around the eye.

In acute presentations of suspected ERU, your veterinarian might request further testing to determine the specific causative agent and the best course of action for treating the episode.

The primary goal of ERU treatment is to decrease ocular injury and minimize the inflammation of the eye.

Allergens are often linked as a trigger to recurrent episodes of ERU and can often be decreased or eliminated by simply changing the horse's pasture, pasturemate, type of bedding, or even stable.

Decreasing sun and insect exposure is often very helpful and can be accomplished by simply having the horse wear a protective flymask.

Systemic non-steroidal anti-inflammatories can be used, sometimes in combination steroidal agents. Topical steroidal and non-steroidal agents often work well for ERU flare ups but should be used after a veterinary examination, as serious complications (such as corneal ulcers and fungal infections) can result from the use of steroids when there is damage to the cornea.

Atropine ophthalmic preparations are also useful for dilating the equine eye and helping to alleviate some of the pain produced by uveal inflammation. Again, these should only be used with veterinary oversight as atropine has been linked to development of colic when used excessively.

The ultimate prognosis for eyes affected by ERU is poor at best. Recurrent episodes of ERU eventually lead to development of vision deficits; therefore, trying to reduce the occurrence of flare-ups is the primary concern when treating ERU horses.

Surgical therapy is available for horses in some areas. These options might include implantation of sustained release cyclosporine devices and vitrectomy (a removal of some or all of the aqueous humor from the eye). However, surgical options are not without side effects and should be discussed thoroughly before deciding whether these are practical solutions for a horse suffering from an increased frequency of ERU episodes.

About the Author

Kristen Slater, DVM

Kristen Slater, DVM, practices with Kasper & Rigby Veterinary Associates in Magnolia, Texas. Her practice interests include preventive medicine, reproduction, sports rehabilitation, and conditioning.

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