Uveitis (other names include moon blindness and periodic ophthalmia) is a painful and potentially very serious condition – it is the most common cause of sight loss in horses. Uveitis simply describes inflammation within the eye, this affects three different parts of the eye – the blood
supply to the eye, the muscles controlling the diameter of the iris, and the iris itself.
This inflammation can be initiated in a number of ways, and any damage or irritation to the eye can initiate a reflex inflammatory response. This includes physical trauma, and corneal diseases such as ulcers. Uveitis can also commonly be immune-mediated (especially in Appaloosas), and may affect
one or both eyes recurrently. Geographically, the causes of uveitis vary greatly, and some of the infectious causes that commonly affect horses in other countries are currently being investigated in the UK.
The most common signs that your horse may display are squinting, watery discharge, rubbing his eye and being uncomfortable in bright sunlight. On closer inspection, the inside of the eye may appear “hazy”, you may also notice that the pupil appears very small and narrow, even in a dark stable.
It is important that every painful eye is examined by a vet as soon as possible, as some diseases may present similarly but require very different treatments.
The mainstay of treating uveitis is using anti-inflammatory drugs to reduce inflammation and pain. We will prescribe steroid-based eye drops for you to administer daily, and in addition to this we will put drops in the eye to dilate the pupil.
This is because the inflammation causes the muscles controlling the iris to go into spasm – these drops relax the pupil and relieve the pain caused by this spasm. Often the horse will be given oral pain relief. We may recommend that you continue treatment for a few weeks past resolution of the clinical signs.
Managing a Horse With Uveitis
It is important to keep the horse in a darkened stable, especially if eye drops have been given. This may then progress to being turned out in a good quality UV protective fly mask. It is important to monitor a horse who has had uveitis, as very often it may be part of a syndrome of recurrent disease. For horses that suffer from repeated episodes of immune mediated uveitis further treatment options are available, including surgical implants that release drugs within the eye to prevent the horse’s immune system from causing uveitis.
Long Term Problems
It is important to try to control uveitis, as if it remains untreated significant damage can be caused to the eye, and can ultimately result in total vision loss. When a horse is vetted, the vet will carefully examine the eyes to look for previous signs of uveitis.
The picture shows a Miniature Shetland whose uveitis was uncontrolled after a blunt trauma to the eye. The pale disc you can see is the Optic Disc – which is the head of the nerve connecting the retina to the brain!