Equine recurrent uveitis

"Moon blindness" on anIcelandic horse

Advanced stage of disease

Advanced stage of disease

ERU on anIcelandic horse

Equine recurrent uveitis(ERU) – also known asmoon blindness,recurrent iridocyclitis,orperiodic ophthalmia– is an acute, nongranulomatousinflammationof theuveal tractof theeye,occurring commonly inhorsesof all breeds, worldwide. The causative factor is not known, but several pathogeneses have been suggested. It is the most common cause of blindness in horses. In some breeds, a genetic factor may be involved.

Aetiology

Several aetiologies are suggested, and any combination of these may be present in any given case.

• Vitamin deficiency(A,BorC)
• Viral infection
• Bacterial infection
  • Leptospira
  • Streptococcus
  • Brucella
• Parasitic infection
  • Strongyle
  • Onchocerca cervicalis
• Autoimmunedisease

The disease has been suggested to be primarily autoimmune in nature, being a delayedhypersensitivityreaction to any of the above agents.

Clinical signs

In the acute stage of the disease, acatarrhalconjunctivitisis present, with signs of ocular pain, usuallyblepharospasm,increasedlacrimation,andphotophobia.Miosisis also usually present. After a few days, this will progress to akeratitisandiridocyclitis.Other ocular problems may also occur, including conjunctival andcornealoedema,andaqueous flare.

After an acute flare-up, no clinical signs of disease may be seen for a prolonged period, which can vary from a few hours to a few years. With frequent acute incidents, though, additional clinical signs may be seen, including anterior and posteriorsynechiae,poorpupillaryresponses,cataracts,and a cloudy appearance to thevitreous humour.

Diagnosis

The cornerstone of diagnosis is an accurate history, and a good clinical examination of the eye, to eliminate traumatic uveitis. Ultrasonography is a useful tool, as it can detect a thickenediris,but only in the hands of an expert.

Treatment

During an acute flare-up, therapy is targeted at reducing the inflammation present, and dilating the pupil.Mydriasisis important, as pupillary constriction is the primary reason for pain. Anti-inflammatory therapy is usually given both systemically, often in the form offlunixin meglumine,and topically, asprednisolone acetate.The mydriatic of choice isatropine.In the periods between acute attacks, no therapy has been shown to be beneficial.

Prognosis

Horses that suffer from this disease can never be considered cured, although they can be managed by careful use of the therapy described above, and fast detection of new flare-ups. If the disease is not properly treated, it will eventually lead toblindness.

Epidemiology

ERU occurs in horses worldwide, but is more common in North America than in Europe, Australia or South Africa.Males and females are equally affected.

Genetics

TheAppaloosahas a higher risk of developing ERU than other breeds; this predisposition has a genetic basis. Appaloosas which develop ERU are more likely than other breeds to have ERU in both eyes, and more likely to become blind in one or both eyes.