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Glaucoma
in dogs and cats results from a variety of abnormal
conditions of their eyes which cause a rise in the
pressure of the fluids within the globe.
Normal
intraocular pressure, or IOP, the pressure of fluids
inside the eye, is controlled by a delicate balance
between fluid production and fluid removal. Specifically
this fluid is aqueous humor, produced in the posterior
chamber of the eye (behind the iris) by the ciliary
body. The iris is the portion of the eye that provides
"eye color" and which opens and closes to make
the pupil larger or smaller. Aqueous humor flows between
the iris and the lens to the anterior chamber (in front
of the iris) where it exits the eye via the trabeculae
in the drainage angle, a hidden part of the eye just
beyond the cornea, the clear portion of the front of the
eye. The iris also plays a part in removal of aqueous
humor.
Pressure
measurement is generally performed using a tonometer in
a procedure called tonometry. There are three types in
common use, the Tonopen, the TonoVet (manufactured by a
competing company) and the Schiotz. Tonopen and TonoVet
are fairly automated devices that are considered to give
easy, accurate readings. Some longtime users of the
Tonopen are switching to the TonoVet, while some doctors
don't care for it at all.
Like many
things in practice, it's a personal preference. The
Schiotz tonometer is a mechanical device that gives a
reading, which is then converted to intraocular
pressure. IOP is usually read in millimeters of mercury
by both devices. Normal is considered to be between 10
and 20 for the Tonopen and TonoVet, and 15 and 30 (some
veterinary ophthalmologists use 25 as the upper limit)
for the Schiotz.
When
pressure begins to increase, the eye responds with
redness, "steamy" or cloudy cornea, dilated
and unresponsive pupil, blindness, bulging of the
eyeball. These are the outwardly visible changes and not
necessarily all of them are present in every eye.
Ophthalmoscopic examination by your pet's doctor can
reveal additional changes inside the eye.
Time is
of the essence in diagnosis and treatment of glaucoma.
In short order the high pressure inside the eye will
damage the retina, leading to permanent blindness.
Indeed, approximately half of the patients in whom
glaucoma is diagnosed have already lost vision in one
eye.
The good
news is that vision may be spared for a time in the
other half of affected eyes and unaffected eyes (on the
other side) can be treated prophylactically, perhaps
permanently saving vision in that eye.
In 1980,
when I graduated from
Auburn University's College of Veterinary Medicine
, a glaucoma diagnosis came with good and bad news. The
good news was the medicine to treat glaucoma was cheap.
The bad news was that it didn't work very well, and your
pet would soon go blind.
Today
there is still good and bad news. The good news is that
the medicines we use to both control and prevent
glaucoma work great, and vision can be preserved for
approximately one to one and one half years. The bad
news is that it's pretty expensive.
Modern
medication for glaucoma treatment is typically used
twice daily in affected eyes and once daily in
unaffected eyes predisposed to glaucoma. In the initial
stages of emergency, high-pressure glaucoma medications
might be used much more often until the problem is
controlled.
If one
eye becomes glaucomatous, it is just a matter of time
before the other one is also affected. Dr.
Laurence Galle
, ACVO, calls them "yet-to-be-affected eyes."
Some
glaucomatous eyes that fail to respond to topical
medications will improve with surgery performed by a
board-certified veterinary ophthalmologist. Your pet's
doctor can refer you if that becomes necessary.
Untreated
and uncontrolled glaucoma is a very painful condition.
Imagine lying on your back with a brick balanced
standing on end on one of your eyes. Now balance five
more bricks on top of that one. The pressure is
unbearable and the pain and headache soon wear down the
happiness, immune system and overall health of the
affected dog or cat. When your veterinarian tells you
that your pet has glaucoma you must either begin
treatment or, if you cannot afford it, allow the doctor
to remove the eye (especially if it is no longer
visual).
Likewise,
if treatment has failed and IOP cannot be controlled,
please allow your veterinarian to surgically remove the
eye(s).
In
summary, we are blessed to have medications that can
almost always control canine and feline glaucoma with
ease, at least for a time. It no longer carries a
prognosis of "go home and go immediately
blind." There may be sacrifices to make to afford
your pet's glaucoma medication, but the reward of a
visual pet is more than worthwhile.
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