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Equine Uveitis—A New Paradigm

Dr. Tim Knott refers to equine recurrent uveitis (ERU) as a recurrent “acute on chronic” inflammatory disease that includes a “spectrum” of diseases.
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Knott remarked that no matter the cause, any horse with uveitis is at risk of developing equine autoimmune uveitis (EAU).

Tim Knott, BSC (Hons), BVSc, Cert-Vet Ophthal, MRCVS, of the Equine Eye Clinic in Britain, presented on uveitis at the 2019 BEVA Congress. He described how classic equine recurrent uveitis (ERU) is likely not just a number of recurrent episodes of acute anterior uveitis with periods of quiescence and lack of clinical signs, but rather is a long-term inflammatory process that involves acute episodes. He refers to ERU as a recurrent “acute on chronic” inflammatory disease that includes a “spectrum” of diseases.

Knott divides the spectrum into the following:

  • Simple uveitis that has an identifiable cause such as blunt trauma, ocular perforation, corneal infection or systemic disease that damages the blood ocular barrier;
  • Complex or syndromic uveitis that is either a) chronic uveitis +/- acute uveitis with an identifiable cause such as leptospirosis, or b) equine autoimmune uveitis (EAU) with no identifiable cause.

He also classifies ERU into these clinical syndromes:

  • Type 1 equine autoimmune uveitis (EAU);
  • Type 2 chronic uveitis secondary to systemic disease, such as endoparasites or liver abscess;
  • Type 3 chronic uveitis secondary to ocular disease, including leptospirosis or stromal abscess.

Knott remarked that no matter the cause, any horse with uveitis is at risk of developing EAU. He recommended ruling out systemic disease and implementing aggressive anti-inflammatory measures with systemic steroids, NSAIDs and ocular steroids. The blood-ocular barrier can be stabilized with atropine.

Ocular steroids—either topical or subconjunctival—can be used for a month following clinical resolution, but other immunosuppressive treatments can be used. These can include suprachoroidal cyclosporine implants or injection of cyclosporine-like drugs and steroids.

He suggested that intravitreal low-dose gentamycin (4 mg with no preservatives) could be useful for confirmed leptospirosis lesions, but this is still only an experimental treatment. At the 2020 AAEP Convention Table Topic on Ophthalmology, Carol Clark DVM, DACVIM, noted that there have been reports of detached retinas and catastrophic ocular changes following use of intravitreal gentamycin.

In all cases of uveitis, Knott stressed that it is important to protect and support the cornea, which tends to develop problems secondary to uveitis. He likes to use autologous serum and hyaluronate for this purpose. 

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