Download Uveitis In Horses - Seattle Animal Eye Clinic

ANIMAL EYE CLINIC INFORMATION SERIES!
www.seattleaec.com
Uveitis in Horses
Anatomy of the eye
The Uvea
Uveitis is the leading cause of blindness in
horses. The word “uveitis” means inflammation
inside the eye. The uvea is the middle layer of the
eye. It includes the iris, the ciliary body, and the
choroid. Inflammation of these structures can
result from many causes, and can result in damage
to structures inside the eye, potentially leading to
vision loss and discomfort.
!
PAGE 1
ANIMAL EYE CLINIC INFORMATION SERIES!
www.seattleaec.com
WHAT IS UVEITIS?
Uveitis is inflammation of the inner
middle layer of the eye. Inflammation
can result from many causes, and basically means swelling, redness, oozing.
Just as a finger will swell, turn red, and
become painful if struck by a hammer
or becomes infected, the uvea can
swell, become red, and leak protein,
fluid, or white blood cells when inflamed. Many horses develop a long
term recurrent uveitis- Equine Recurrent Uveitis (ERU), also called
“Moon Blindness”.
WHAT ARE THE CAUSES OF UVEITIS IN HORSES?
Uveitis can result from trauma (blunt or penetrating), various types of infection within the
eye, certain types of cancer, or due to autoimmunity.
!
Trauma: Just as a finger swells and turns red when struck by a hammer, the layers
of the eye will swell & become inflamed when subjected to trauma. This can be a blunt injury, or some type of penetrating injury. Typically the inflammation subsides on its own
over time, but permanent damage to the eye can result.
!
Infection: Inflammation is one way the body fights infection. It allows the body to
send antibodies, white blood cells, and other disease-fighting molecules to the site of infection. Uveitis can result from infections inside the eye (bacterial or fungal), or on the surface
of the eye (cornea).
!
Cancer: Various types of cancer can result in uveitis. Solitary tumors inside an eye
will cause inflammation as they grow within the normal tissues. These can be primary tumors- i.e. started in the eye, or metastatic tumors- i.e. spread to the eye from some other
place in the body. Cancer elsewhere in the body can also cause the immune system to attack the eye inappropriately- so called paraneoplastic uveitis.
!
Autoimmunity: This is by far the most common type of uveitis in horses. In this
situation the body’s immune system has become sensitized to uveal tissue- it regards these
normal intraocular structures as a dangerous foreign invader and attacks the uvea as if it
!
PAGE 2
ANIMAL EYE CLINIC INFORMATION SERIES!
www.seattleaec.com
were a bacteria or virus. The cause of this sudden change is unknown. This is similar to
other autoimmune conditions like Lupus, Rheumatoid arthritis, etc...
Equine recurrent uveitis, as the name implies, is a disease in which the eye(s) becomes inflamed time and time again. The majority of cases are believed to be auto-immune in nature. Something- trauma, disease, genetics, sensitizes the
immune system so that it now
thinks that the uveal tissues are
foreign, and must be eliminated. From time to time the
body attacks the eyes, trying to
rid itself of the persisting “foreign” presence, as if the uvea
were a bacteria or viral invader
that needed to be cured. In
some cases there can actually
be a persistent infection. A
bacterial infection- leptospirosis, has been found to be a cause of ERU. Leptospirosis can be carried by wild rodents, raccoons, and other animals, and can be shed in their urine. Horses in areas frequented by infected wild animals can become infected as well. This usually results in a brief mild illness,
but the bacteria can get into the vitreous- the transparent gel that fills the back of the eye.
In this location the bacteria can “hide” from the immune system. From time to time the
body realizes that the bacteria are there and attacks the eye. This is not a common cause in
the Pacific Northwest region of the United States. In parts of Europe it has been found to
be the leading cause of equine uveitis.
Based upon the specific historical and ophthalmic findings in your horse, your doctor may
suggest various tests to help determine the specific type of uveitis.
WHAT HAPPENS WHEN THE
UVEA IS INFLAMED?
In most cases active uveitis is uncomfortable. Horses are light-sensitive, the pupil
will often become very small (constricted),
the eye may become very cloudy or change
color. In the short term vision can be affected by increased murkiness of the in!
PAGE 3
ANIMAL EYE CLINIC INFORMATION SERIES!
www.seattleaec.com
traocular fluids. Inflammation can lead to permanent damage to structures within the eye
as well. Damage to the lens can lead to cataract formation. Damage to the drain inside
the eye can lead to increasing pressure as fluid is unable to exit normally (glaucoma). Fluid
can leak from the back wall of the eye separating the retina from the wall (retinal detachment). Every time the inflammation is active, additional damage is done, so keeping uveitis controlled is very important if vision and comfort are to be maintained.
HOW IS UVEITIS TREATED?
When a specific cause is discovered, treatment includes specific therapy directed at that
cause. In addition to these specific therapies we would employ antiinflammatory medications. These might include corticosteroids like prednisone and dexamethasone (drops and/
or tablets depending on severity and part of the eye involved) and nonsteroidal antiinflammatory medications (NSAIDs). Both treat inflammation, but steroids have the additional
benefit of suppressing the immune system’s reactivity. Cyclosporine is an antirejection drug
which can also reduce the frequency and severity of episodes. In certain cases we can implant a slow release cyclosporine implant into the eye to provide continual treatment. This
surgery can often be performed as a standing procedure, and the implants are very well tolerated. Often we will treat with drops to dilate the pupil, as much of the discomfort associated with uveitis results from spasm of the muscles that constrict it. Dilation therefore improves comfort. Autoimmune uveitis usually requires lifelong treatment to maintain control, although medications are usually decreased over time to reduce potential side effects.
Your ophthalmologist will discuss the treatment options based upon your animal’s individual situation.
WILL MY HORSE LOSE VISION COMPLETELY?
This is possible- even with all available
treatment. Your doctor will discuss the
prognosis for your horse based upon the
stage of disease and treatments selected. It is important to keep in mind
that many blind horses enjoy a good
quality of life as long as comfort is maintained in a protected and loving environment.
!
PAGE 4