Glaucoma is caused by an increase in fluid pressure
within the eyeball. Normally, there is a continuous (although very slow)
exchange of fluid between the eyeball and the venous circulation. Anything that
upsets this delicate balance can cause a buildup of pressure and produce a
hard, enlarging eye. When pressure within the eye becomes greater than the
arterial blood pressure, arterial blood cannot enter the eye to nourish the
Inflammations and infections within the eye are the most common causes of
acquired or secondary glaucoma in cats (see Uveitis). Other causes are cataracts, eye injuries, and
cancers within the eye. A lens that is out of alignment may block the outflow
of aqueous fluid. Primary (congenital) glaucoma is rare but has been observed
in Persians, Siamese, and domestic shorthairs.
The following information isn’t intended to replace regular visits to your veterinarian. If you think your cat may have feline infectious peritonitis, please see your veterinarian immediately. And remember, please do not give any medication to your pet without talking to your veterinarian first.
A cat suffering from acute glaucoma exhibits mild to moderate tearing and squinting and there is a slight
redness to the white of the eye. The affected pupil is slightly larger than the
opposite pupil. The eye is painful when gently pressed and feels harder than
the other eye. As fluid pressure increases to greater than 30 to 50 mmHg, the
eye becomes noticeably larger and the surface begins to bulge. (Normal pressure
is 10 to 20 mmHg.) In time, the retina is damaged. The lens may be completely
or partially pushed out of alignment. This entire sequence can occur suddenly
or over a matter of weeks.
To diagnose glaucoma, intraocular pressure is measured with a technique
called tonometry, which uses an instrument placed on the surface of the eye.
The interior of the eye must also be examined, and a procedure called
gonioscopy checks the flow of fluid out of the eye. Ultrasound may also be used
to evaluate the eye.
Every effort should be made to distinguish glaucoma from conjunctivitis and uveitis,
both of which produce similar signs. It is critical to begin treatment of
glaucoma before irreversible injury occurs to the retina. Some permanent vision
may be lost before the disease is discovered.
Treatment: Acute glaucoma may require emergency hospitalization.
Veterinarians use various topical and oral drugs to lower intraocular pressure.
Mannitol may be used in the short term to lower pressure.
Maintenance drugs are used for chronic glaucoma. These might include
carbonic anhydrase inhibitors topically or orally and, possibly, pilocarpine.
Any underlying eye disorder should be treated. Treatment is for the life of the
Failure to respond to medical management may suggest surgery is needed, if
there is a potential to retain some vision. Surgery may try to decrease the
fluid production or increase the rate of fluid escape from the eye, this
reducing pressure within the eye. For an eye that is blind and painful, the
best approach is to remove the entire eye. A prosthesis can be inserted for
It is felt that some glaucoma damage results from secondary nerve damage due
to the cellular chemical glutamate. Glutamate is an amino acid and is extremely
toxic to the retinal ganglion cells; basically, it overstimulates them. Drugs
that block glutamate receptors, and calcium channel blockers-used to protect
the retina and optic nerve-are being studied for possible therapy.
WebMD Veterinary Reference from "Cat Owner's Home Veterinary Handbook"