Uveitis means inflammation of the uveal tract, an internal structure of the eye made up of the iris, ciliary body and choroid. It can occur as a primary disease or secondary to other conditions affecting the eye such as trauma or corneal ulcers.

The exact cause of a primary uveitis is unknown. Current thinking is that it is a hypersensitivity reaction to a bacteria or to a disease process occurring elsewhere in the body, however this theory has not yet been proven. Some horse will develop equine recurrent uveitis (ERU, also known as ‘moon blindness’). As the name suggests this is a recurring condition where the horses suffer from repeated episodes of uveitis. The severity of the condition and the interval between episodes varies with each individual.

Common clinical signs of uveitis:

  • Squinting or full closure of the eye
  • Excessive tear production
  • Corneal oedema (Cloudy or ‘blue eye’)
  • Constricted pupil
  • Photophobia an increased sensitivity to light, the eye will appear more painful when in daylight than in a dark stable


If not treated promptly and aggressively uveitis can lead to long term complications such as adhesions between the iris and cornea and in very severe cases, blindness. The aim of the treatment is to reduce pain and inflammation within the eye and to dilate the pupil in order to provide pain relief and to prevent adhesions. This usually involves the following treatments:

  • Topical steroids
  • Topical atropine: this dilates the pupil and is given to effect until full dilation is achieved, this can be up to four times daily. High doses of atropine can slow the movements of the guts resulting in impaction colic, therefore the minimal dose possible is used to achieve the required result.
  • Systemic anti inflammatory medication such as phenylbutazone or meloxicam

Horses must be kept out of bright light at all times during treatment as the pupil is not able to constrict in response to light as would naturally occur, due to the effects of the atropine.


The prognosis for uveitis is always guarded. A single case of uveitis that is well managed can fully resolve with no long term side effects. In cases of ERU, when the attacks are frequent and severe, the pain can sometimes become unmanageable and surgical removal of the eye can be the only option. In most cases the greater the interval between episodes the better the prognosis.