What is it?

Uveitis, in the most basic breakdown of the word, means inflammation of the uveal tract of the eye. This consists of the iris (colored portion of the eye), the ciliary body (which changes the shape of the lens and produces aqueous humor, the liquid present in the front of the eye), and the choroid (the vascular portion of the eye). This is a relatively common disease, and is the leading cause for blindness in the horse.

 As a species, horses are especially susceptible to developing episodic flares of uveitis, in which case, the disease is called Equine Recurrent Uveitis (ERU), which is commonly known as Moon Blindness. If uveitis is left untreated or does not respond to appropriate treatment, the condition is very painful and can lead to blindness of the affected eye or eyes.

DID YOU KNOW?

The origin of the term “Moon Blindness” is from the 1600’s due to people thinking the cyclic nature of the uveitic flare-ups correlated with the phases of the moon. The name “Moon Blindness” has stuck throughout the centuries despite it since being shown that the phases of the moon and active ERU episodes have no correlation!

What causes it?

  • Trauma to the eye

  • Ulceration of the cornea

  • Tumors of the eye

A variety of things can cause uveitis because of the horse’s body having an inflammatory response to the trigger, but not because the trigger causes uveitis directly. For example:

  • Systemic infection (such as leptospirosis)

  • Autoimmune disease

  • For horses with ERU (compared to a single episode of uveitis) - pain/stress elsewhere in the body can set off a flare-up

There is also some breed disposition for Equine Recurrent Uveitis as well, with Appaloosas and Draft Breeds being overrepresented in both incidence and the severity of the cases.

What are the clinical signs?

The most common signs of uveitis in horses include:

  • Squinting / holding the eyelid shut

  • Tearing

  • A blueish haze to surface of the eye

  • Swelling or redness of the eyelid

  • Constriction of the pupil

NOTE: Many of these clinical signs overlap with the signs of a corneal ulceration, which is a different disease and MUST be treated differently than uveitis.

How is it diagnosed?

You veterinarian will make a diagnosis based off of a complete ophthalmic exam. In some cases, additional diagnostics may be necessary to rule in or out other diseases that may be the cause for a uveitic episode, so that appropriate therapy can be prescribed.

In the case of an active flare-up, it is of the utmost importance that a corneal ulceration is ruled out prior to beginning treatment with topical steroids. If you horse has 2 or more instances of uveitis, a diagnosis of Equine Recurrent Uveitis can be made.

What is the treatment?

In acute instances uveitis is treated with:

  • Systemic NSAIDs

  • Pupillary dilation medications

  • Topical steroid

  • If the incident can be attributed to the onset of another disease, such as a systemic bacterial infection, efforts should also be made to cure or control the primary disease process.

In chronic cases where the affected eye does not respond to treatment, and/or where vision is no longer present, it may be recommended by your veterinarian to have the eye enucleated, or removed. This can be a very difficult decision to make on behalf of our equine companions. However, the vast majority of people who elect to have enucleation performed on their horse when it has been recommended for reasons of chronic uveitis find that it has a very positive outcome overall, with the horse sometimes even having a dramatic change in temperament as a result of no longer having chronic pain in the affected eye.

VIGILANT MONITORING AND QUICK, APPROPRIATE THERAPY IS VITAL FOR THE SUCCESS OF TREATMENT OF UVEITIS. IF YOU SUSPECT YOUR HORSE HAS SIGNS OF UVEITIS, PLEASE CALL YOUR VETERINARIAN IMMEDIATELY