May
27
Written by:
Surgi-Care Center for Horses
5/27/2011 4:59 PM
Equine
Recurrent Uveitis (ERU), an immune-mediated disease, is one of the most common
causes of blindness in horses. ERU is commonly referred to as “moon blindness”
and is believed to have several possible causes including bacteria, parasites, viruses,
trauma and immune system disorders. ERU is characterized by increasingly frequent
bouts of irritation and inflammation in the eye (uveitis).
Uveitis
can be extremely painful. Common signs associated with uveitis are small pupils,
discharge from the eyes, squinting, red eyes and conjunctiva, swelling around
the eye, and sensitivity to light. Other signs may include corneal edema
(cloudy cornea), loss of balance, abnormal gait or tripping, rubbing the eye,
or even pus inside the eye.
The
most common bacteria associated with uveitis is Leptospira. Horses with Leptospirosis
may have acquired it from drinking water or eating feed contaminated with urine
from another infected animal. Leptosporosis can also be spread from animal to animal
by human contact. Horses with a leptospira infection may also have a fever, become
anorexic, have abnormal milk production, as well as the eye related problems.
Onchocerca
is a common parasite associated with ERU. This Culicoides fly, also known as
the “biting midge” or “no-see-um” is believed to be the primary means of transmission.
Horses affected by Culicoides may show sores on the abdominal midline and along
the base of the mane or withers. ERU occurs when the horse mounts an immune
response to the parasite and the eye has enough of the parasite antigen (something
from the parasite that the immune system attacks) that it becomes irritated.
Eye
trauma is another important cause of equine uveitis. Any blunt or penetrating
injury, eye surgery, corneal ulcers or infection may cause trauma to the eye
and subsequent inflammatory irritation. Equine herpes and influenza viruses
have been linked to uveitis in the horse. Allergies have also been implicated
in cases of uveitis.
Topical atropine will dilate
the eye and reduce pain associated with the constricted pupil. Topical
antibiotic ointments will help fight or prevent any bacterial infections.
Topical steroids may be indicated to reduce inflammation, however, the eye
should be examined by a veterinarian prior to use of steroid. Non-steroidal
anti-inflammatories such as Banamine, or phenylbutazone can also help reduce
inflammation. Wearing fly masks and keeping the horse out of direct sunlight
will help relieve irritations from light, dust or insects.
When
uveitis occurs frequently in a horse, it becomes a case of ERU. One episode of uveitis
may have cleared up, but the same or another cause will stimulate a recurrence.
These additional bouts of uveitis may become more frequent and less responsive
to treatment. It is important to treat these horses aggressively when episodes
occur in order to have the best chance to avoid loss of vision. If your horse
begins showing signs of uveitis, it is important to contact your regular
veterinarian for an eye examination.
Contact
Surgi-Care Center for Horses at 813-643-7177 or email lkuebelbeck@surgi-carecenter.com with
any questions regarding this topic.