Equine uveitis

See us perform an implant on a patient Animal Madhouse, Channel 4

It is important to understand that there are many manifestations of uveitis in the horse. The term uveitis means inflammation of the uveal tract which is made up of the iris, ciliary body and retina. There are many proposed cause of this inflammation. Some can be infections - e.g. Leptospirosis, or as a result of trauma, neoplasia or immune mediated disease.

The disease can present in different patterns

1. Single episode of uveitis

These may be self-limiting if the cause, such as a trauma, heals. It may require a short duration of medical management to achieve complete resolution and to provide effective pain relief. Clinical signs are pain, ocular discharge (usually clear), redness, pus in the front of the eye and constriction of the pupil.

Sometimes the eye will be correctly medicated and the inflammation will appear to resolve. A few days or weeks later and the eye may become inflamed again. In these cases prolonged treatment after resolution of the clinical signs may lead to a complete resolution with no evidence of recurrence.

2. Sub-clinical or insidious uveitis

These cases often present as finding at a vetting or, in late stages, as blindness. The majority of the cases have a yellowish reflection from the back of the eye due to changes in the vitreous (the jelly behind the lens). There may also be cataract formation. The iris may darker and a permanent pupil constriction present. Despite these changes, the eye is often comfortable. Coloured horses appear to be more commonly affected.

3. Classic equine recurrent uveitis

These cases have multiple discrete instances of inflammatory. Acute clinical signs are a clear ocular discharge, pain, corneal oedema, pupil constriction and pus in the anterior chamber (clear fluid at the front of the eye). Chronic changes include corneal oedema, iris hyperpigmentation and loss of mobility, cataracts and vitreal degeneration. Episodes of acute disease can be seasonal and may only occur once a year. Most owners report increased episodes when the eye is exposed to wind or sunlight but there is no research to establish this as fact. Long-term the inflammation will lead to loss of vision and is painful each time an episode occurs.

Treatment

Effective treatment of equine recurrent uveitis can be difficult to achieve. Some horses cope well with long-term anti-inflammatory medication either in the form of eye drops or orally. However, this is not necessarily ideal as there are side effects of the medications.

It is now possible to implant a slow release device into the eye that delivers a drug called cyclosporine to the uveal tract. It has to be implanted as the drug cannot cross the external coat of the eye if given topically. This treatment has allowed some horses to come off all medication without any episodes of recurrence even beyond the recognised lifespan of the implant. Not all cases respond perfectly but it can make a major difference to the majority of horses who suffer from this disease.

An alternative therapy is removal of the vitreous from the eye to prevent further attacks. This has a good success rate as well but is best reserved for those cases with vitreal changes.