Exophthalmos, Enophthalmos, and Strabismus
Exophthalmos, enophthalmos, and strabismus are all diseases in which the cat's eyeball is abnormally positioned. With exophthalmos, the eyeball protrudes, or bulges, from the orbit of the eye. This may be due to a space-occupying mass behind the eyeball. Enophthalmos causes the eyeball to recess or sink into the skull. This is possibly because there is a mass in front of the eye, or because the eyeball itself has lost volume, becoming smaller in size. Strabismus is when the eye appears to look off at a different angle, unable to focus in the same direction as the other eye. This can occur with one, or both eyes. It can also be referred to as crossed eyes. Strabismus is caused by an imbalance of extraocular (outside of the eye) muscle tone, or it may be caused by something decreasing the mobility of the muscles surrounding the eye.
The condition or disease described in this medical article can affect both dogs and cats. If you would like to learn more about how this disease affects dogs please visit this page in the PetMD pet health library.
Symptoms and Types
The signs for each of these disease are as follows:
- General malaise
- Swollen eyelid
- "Cherry eye"
- Loss of vision
- Pockets of pus in or around the eye (orbital abscess)
- Discharge from the eyes that is watery (serous) or mucous mixed with pus (mucopurulent)
- Lagophthalmos (inability to close the eyelids completely)
- Inflammation of the cornea (transparent coating of the eye) or surrounding tissue
- Pain on opening the mouth
- "Cherry eye"
- Wasting of the muscle surrounding the eye (extraocular muscle atrophy)
- Deviation of one or both eyes from the normal position
- Decreased functioning of the muscles surrounding the eye
Exophthalmos is generally due to a space-occupying mass located behind the eyeball. Conversely, a mass located in front of the eye may cause enophthalmos; this disease is common in cat breeds with long, narrow heads. Strabismus, or "crossed eyes," is usually caused by an imbalance of extraocular (outside of the eye) muscle tone. The Siamese cat is highly susceptible to this eye disease.
Some other factors that may lead to these eye diseases include:
- Bleeding within the eye
- Pockets of pus within the eye
- Inflamed eye tissue (bacterial or fungal in nature)
- Inflamed or swollen sac of mucous in the bone that surrounds the eye socket (not found in cats)
- Inflammation in the muscles surrounding the eye(s)
- Arteriovenous fistula (when arteries join with veins, and a new, abnormal passage is formed); this is rare
- Dehydration (it affects the water content within the eyeball)
- Drooping eyelid
- Constricted pupils
- Collapsed globe
- Loss of volume in the eyeball (i.e., the eyeball is shrunked and usually non-functional)
- Horner’s Syndrome (a lack of nerve distribution to the eye and/or a loss in the supply of nerves)
- Restriction of eye muscle mobility from scar tissue (usually from previous trauma or inflammation)
- Abnormal crossing of visual fibers in the central nervous system
You will need to give a thorough history of your pet's health, onset of symptoms, and possible incidents that might have preceded this condition. Your veterinarian will perform a thorough physical exam, examining the eyeballs, surrounding bone and muscle, and looking in your pet’s mouth for any abnormalities. X-ray images of the skull will help to determine the exact location of any growths, pockets of fluid, or abnormalities in the muscle or bone that might be contributing to the abnormal positioning of the eyeball. Your veterinarian will also probably want to perform basic blood tests, including a chemical blood profile, a complete blood count, a urinalysis, and an electrolyte panel, just to make sure there is no underlying systemic disease involved.