Glaucoma
In Cats
Glaucoma
is abnormally high pressure in the eye. Inside the normal eye there
is constant production and drainage of a watery fluid called aqueous
humor. When there is a problem with the drainage of this fluid,
the pressure within the eye can increase. High pressure causes damage
to the optic nerve, which, in turn, causes vision loss. Causes of
glaucoma can be primary (spontaneous) or secondary.
Primary
Glaucoma
Primary glaucoma indicates a problem in the area where fluid leaves
the eye. The problem can be structural or one that involves the
function of the drainage area of the eye. This form of glaucoma
has a tendency to be inherited and is very rare in the cat.
Secondary
Glaucoma
Secondary glaucoma develops as a side effect of some other disorder
within the eye. Many different eye diseases can interrupt the usual
flow of aqueous humor within the eye or disrupt the drainage of
this fluid from the eye.
Causes
of Glaucoma
The
exact precipitating cause of primary glaucoma is unknown. The disease
appears to occur spontaneously, often without any warning. Even
though the drainage area of the eye may be abnormal since birth,
it is not understood why acute glaucoma appears at a particular
time, later in life.
Secondary
glaucoma is the most important form of glaucoma in the cat and has
numerous causes, including the following:
Inflammation – Severe inflammation in the eye produces
protein and debris that circulate with aqueous humor. This material
can clog up the drainage area and block the outflow of fluid. Fluid
flow may also be blocked at the pupil if an inflamed iris sticks
to the lens, which sits immediately behind it. Chronic inflammation
of the iris is the most common cause of glaucoma in the cat.
Lens luxation – If the lens becomes dislocated (luxated)
and falls into the front chamber of the eye, it can block the flow
and drainage of aqueous humor. Lens luxation in the cat is usually
a side effect of chronic inflammation of the iris and adjacent tissues.
Tumors – Tumors inside the eye can invade the drainage
area and prevent fluid from leaving the eye.
Trauma – If the eye somehow gets injured, it can fill
with blood, which may block the drainage pathway.
What
to Watch For
- Red
eye
- Very
squinty and painful eye
- Tearing
- Dilated
pupil that doesn’t react to light
- Cloudy
(whitish/blue) cornea (front surface of the eye)
- Enlarged
size of the eye (known as buphthalmos)
- Vision
loss, blindness
Glaucoma
generally only affects one eye initially. Depending on the underlying
cause of the glaucoma, the other eye may be at risk for developing
glaucoma in the future.
Diagnosis
Diagnostic
tests are needed to recognize glaucoma and exclude other diseases.
Tests may include the following:
A
complete medical history and general physical examination of your
pet. The need for blood work and other general health tests varies.
A
complete exam of the eye to confirm the presence of glaucoma and
to determine if the glaucoma is primary or secondary. The eye is
also assessed for the amount of damage has been done to the optic
nerve and retina. Your veterinarian may refer your cat to a veterinary
ophthalmologist for a comprehensive examination of the eye, which
would include:
Frequent
measurements of the pressure inside of the eye (called tonometry)
Gonioscopy
to evaluate the drainage pathway with special instrumentation
Ultrasonography
of the eye if the eye is too cloudy to be examined in depth. It
can help identify lenses that are out of place, tumors, and damage
to the optic nerve.
Treatment
The
primary goals of the treatment of glaucoma are to treat or correct
any underlying causes, to decrease the pressure within the eye,
and to save vision if possible. Treatment of glaucoma in cats may
be medical or surgical.
Medical
Therapy
Medical therapy is commonly used when inflammation of the eye is
the underlying cause of the glaucoma. Medications are given to decrease
the production of fluid inside of the eye, and to control the inflammation.
Unfortunately, there are no medications that significantly improve
the outflow of fluid from the eye. Glaucoma medications include
topical drops and systemic pills. Anti-inflammatory medications
are available both as ointments and topical drops.
Medical
therapy can also be tried in cases of primary glaucoma.
Surgical
Therapy
Surgical
therapy is sometimes used for treating primary glaucoma that is
unresponsive to medical therapy in the cat. Such surgical therapy
involves killing the area within the eye that produces aqueous humor.
This may be done with either cryotherapy (freezing) or laser therapy.
Another option involves bypassing the drainage area by inserting
tubing with a valve into the eye. All of these procedures are performed
more frequently in the dog.
Surgical
therapy for lens luxation involves opening the eye and removing
the dislocated lens manually.
When
a tumor is present in the eye and causing glaucoma, surgery to remove
the eye (enucleation) is indicated.
When
glaucoma does not respond to medications and the pressure within
the eye remains elevated, when the animal is persistently painful,
or when the eye is blind and medical therapy is too expensive to
continue, then surgical removal of the eye may be considered.
Home
Care
Glaucoma
is often a very difficult problem to treat. Medications must be
administered at consistent times and must often be continued indefinitely.
It is important to administer glaucoma medications exactly as your
veterinarian prescribes them. Medications should not be stopped
just because the appearance of the eye has improved. In the event
that vision cannot be saved, understand that such vision loss is
not life threatening and the vast majority of cats adjust very well
to impaired vision or blindness in one or both eyes.
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