Uveitis (Moon Blindness)

Image of vet examining a horse eye.

Equine recurrent uveitis (also known as Moon Blindness or periodic ophthalmia) is one of the most common diseases that affect the eyes of adult horses. It is also the most common cause of blindness in horses, which makes prompt diagnosis and treatment of this condition essential.

Causes of Equine Recurrent Uveitis

Uveitis is caused by damage to the uvea (or uveal tract) in the eye. The uvea lies just below the white of the eye (sclera) and has three parts:

  • Iris, or the colored part of the front of the eye
  • Choroid layer, which contains connective tissue and blood vessels
  • Ciliary body, the part of the eye that secretes the transparent liquid that is found inside the eye

The underlying cause of uveitis is not known, but several factors may damage the uvea, including:

  • Abscesses in a tooth root
  • Bacteria, such as Brucella, Streptococcus or Toxoplasma
  • Equine viruses, such as influenza or adenovirus
  • Hoof abscesses
  • Parasitic worms
  • Trauma

A horse with equine recurrent uveitis often alternates between periods of inflammation of the uvea and times when there are no signs at all. However, the horse may continue to experience mild inflammation even during the “inactive” periods.

Symptoms of Equine Recurrent Uveitis

Uveitis can affect one or both eyes. If both eyes are affected, one may have greater inflammation. The most common symptoms of active uveitis include:

  • Cloudiness of the cornea
  • Contraction of the pupil
  • Frequent squinting
  • Watery eyes

During an active episode, inflamed cells may also enter the choroid or retina; the retina may partially separate from the underlying tissue; bleeding may occur in the retina; or the vitreous fluid inside the eye may become hazy.

Over time, repeated periods of inflammation can lead to other problems, including:

  • Breakdown of the retina, the light-sensitive structure on the back of the eye
  • Cataracts, a cloudiness of the lens of the eye
  • Formation of fibrous tissue in the iris
  • Glaucoma, a buildup of pressure inside the eye
  • Scarring of the cornea, the clear dome on the front of the eye

Treatment for Equine Recurrent Uveitis

To prevent long-term damage, eye examinations should be a part of a horse’s regular veterinary care. However, horses with chronic uveitis may not have any obvious signs of eye disease.

Treatment depends on the underlying cause. Uveitis may be a sign of another health problem, so an equine veterinarian will conduct a complete physical exam and may order certain blood tests. These can help identify the cause.

If the underlying cause is not clear, topical or whole-body medications may be given to reduce inflammation of the eye and the body.

In addition, horses with uveitis may benefit from good overall care, such as healthy nutrition, routine vaccinations and deworming, keeping the bedding clean, effective fly control and keeping horses away from swampy ponds and pastures.

If you notice any symptoms of uveitis, call us today, so we can assess your horse’s eye and overall health and devise an appropriate treatment plan.