Equine Recurrent Uveitis (ERU or “Moon Blindness”)

Uveitis is a painful inflammation of the eye that can happen as a result of trauma, infection or spontaneously with no apparent trigger factors. Once it occurs more than twice in the same eye, the condition is known as recurrent and can be difficult to manage.

In some unfortunate cases, the disease leads to permanent loss of vision. Prompt diagnosis and treatment is essential to minimise the likelihood of this outcome.

ERU is an immune-mediated disease, meaning that the horses’ own immune system attacks the tissues in the eye. The barriers which normally stop this happening have been breached – sometimes after trauma or infection, but in some horses this seems to happen very slowly over time. Appaloosas and their crosses, German Warmbloods and horses with colour-dilute genes (paleeyes) are pre-disposed to the gradual onset of the condition.

Symptoms of eye inflammation to look out for are excess tear production, squinting and rubbing of the eye, cloudy eye, redness of the edges and aversion to sunlight.

If the inflammation goes untreated, all parts of the eye may become damaged, from the retina, via the lens and iris, to the cornea.

The retina can become scarred, the lens more prone to cataract formation, the iris less flexible leading to it attaching to the lens itself, and the cornea can ulcerate. There is often an increase in the pressure of the fluids inside the eye; this consequence is known as glaucoma.

Treatment includes managing the inflammation and any secondary infection, using oral products and topical eye drops. Eye masks provide UV and wind protection, acting as horse sunglasses. Affected horses must be stabled during daylight hours and turned out at night. A surgical procedure implanting an immunosuppressive drug into the eye is becoming more prevalent in the UK, but is only suitable for selected cases.

If you are concerned about potential ERU, we can perform a thorough examination of the eye to differentiate the condition from other causes of ocular inflammation. Sometimes sedation and nerve blocks are necessary to enable close scrutiny of the eye, as horses have exceptionally strong muscles in their eyelids. Specialist equipment is often needed. North West Equine Vets has just invested in a tonopen, which measures the pressure inside the eye – an important tool in diagnosing ERU.

If you have any concerns, call us on 0808 168 5580