Equine Recurrent Uveitis

Also known as: Periodic ophthalmia — Moon blindness — iridocyclitis — Equine uveitis

Introduction

Equine Recurrent Uveitis is a syndrome that is one of the most common ocular diseases in horses characterised by episodes of active inflammation followed by varying periods of quiescence. The inflammatory events lead to secondary changes and it is the most common cause of blindness in horses.

It is an immune-mediated disease with many potential initiating causes. Damage to the uveal tract may be initiated by trauma or systemic disease.

Conditions and agents which have been implicated include leptospirosis, brucella, strangles, Equine Influenza. Leptospira spp have been the most commonly investigated however their relationship with the disease remains obscure.

Clinical signs

Acute signs of active inflammation include: blepharospasm, epiphora, episcleral injection, corneal edema, aqueous flare, fibrin clots in the anterior chamber and miosis.

Posterior uveitis may involve retinal separation, haemorrhage and a hazy appearance to the vitreous body.

Chronic secondary side effects result, including: corneal scarring, iridal fibrosis, blunting of the corpora nigra, posterior synechiae, glaucoma, cataracts and retinal degeneration.

Diagnosis

The recurrent history and the typical clinical signs are required to make a diagnosis of Equine Recurrent Uveitis. It is important to differentiate between other causes of ocular inflammation such as herpesvirus infection or immune-mediated keratitis.

An attempt should always be made to establish the underlying cause of the disease.

Signs of systemic disease should be sought and haematology and biochemistry might be useful.

Serological testing for Leptospira spp has also been advocated.

Treatment

The goals of therapy are to preserve vision and reduce and control ocular inflammation to minimise permanent damage to the eye.

Often a definitive cause cannot be found and so symptomatic therapy is indicated.

Aggressive topical and systemic anti-inflammatory therapy should be initiated, with drugs such as prednisolone or dexamethasone. Atropine eye drops can be used to reduce pain and the formation of synechiae.

Flunixin is administered systemically and systemic steroids have also been used successfully although care should be taken in the detection of laminitis which can follow treatment.

Initial treatment should be continued for at least 2 weeks and tapered over a further 2 weeks after clinical signs resolve.

Surgical procedures have been developed including core vitrectomy which has a variable outcome.

A cyclosporin drug-delivery device placed underneath a scleral flap adjacent to the ciliary body is currently being developed and shows promising results.

Prognosis

In general, the prognosis for saving vision in horses with Equine Recurrent Uveitis is good, provided owners are diligent in their observation for signs of disease and allow early and aggressive therapy.

In some horses, the severity and frequency of the bouts of inflammation increase, and surgery might be an option to consider.

References

Kahn, C. (2005) Merck Veterinary Manual 9th Edition Merck & Co

Robinson, N. (2009) Current therapy in equine medicine Elsevier Health Sciences