Uveitis - Donkey
Immune-mediated uveitis/recurrent uveitis/uveitis is a very important disease. It can be secondary to keratitis, but is common as a primary immune-mediated disorder. The major problem is its tendency to recur, causing progressive loss of vision. This is the most common cause of blindness.
The causative agent is unknown but several are implicated, such as Onchocerca and leptospira. Regardless of the cause, the treatment is as for uveitis which gives effective, immediate results.
- The acute stage is intensely painful, showing excessive lacrimation and photophobia
- Corneal oedema is a characteristic finding
- Ciliary and conjunctival injection with peripheral corneal vascularisation is also seen
- More serious findings are aqueous flare and hypopyon
- Miosis is always present. Following repeated episodes there may be synechiae, which prevent papillary dilatation in response to mydriatics
- Chronic uveitis results in shrinking of the globe, cataracts and depigmentation of the fundus around the optic nerve
- If diagnosis is attempted, then routine blood tests should be run along with titres for leptospirosis and brucellosis, equine herpes virus, strangles and equine viral arteritis.
- Conjunctival biopsy will diagnose the presence of Onchocerca
Systemic anti-inflammatory treatment is needed urgently to reduce the pain and inflammation. Corticosteroids have been recommended and do work, but the risk of complications makes an NSAID, such as flunixin meglumine, the drug of choice.
- Flunixin meglumine is given every 12 hours for at least five days but should be continued until clinical signs resolve
- If NSAIDs need to be continued for a long period, then a transfer to phenylbutazone will reduce the risk of side effects
- Topical NSAIDs are effective in relieving pain short-term: flurbiprofen 0.03% or suprofen 1% ophthalmic solution
- Topical corticosteroids are safer than systemic but must only be used if corneal integrity is 100%
- Whilst using steroids, regular fluorescein staining must be used to check for ulceration
- If uncomplicated immune-mediated uveitis is diagnosed with certainty, long term topical corticosteroids are recommended, e.g. four weeks
- Topical atropine drops (1-2%) should be applied hourly until mydriasis occurs and then twice daily until the acute inflammatory response has subsided, possibly for up to two weeks. Monitor for gut function as long-term atropine slows gut movement
- Cyclosporin 2% is an ocular immunomodulator, which can produce excellent results but only in about 50% of cases. It can be used to replace corticosteroids if corneal ulceration is present. A ten-day course given at twelve-hourly intervals is recommended
- Grove, V. (2008) Conditions of the eye In Svendsen, E.D., Duncan, J. and Hadrill, D. (2008) The Professional Handbook of the Donkey, 4th edition, Whittet Books, Chapter 11