size and shape of the normal eye is maintained by the amount of
fluid within the eyeball. The pressure of the fluid in the eye is
known as Intra-ocular Pressure (IOP). Fluid is constantly produced
by a structure called the ciliary body. In addition to
producing this fluid (aqueous humor), the ciliary body contains the
suspensory ligaments which hold the lens in place. Muscles in
the ciliary body pull on the suspensory ligaments that control the
shape and focusing ability of the lens.
Aqueous humor contains nutrients and oxygen, which are used by the
structures within the eye. The excess fluid is constantly drained
from the eye between the cornea and the iris. This area is called
the iridocorneal or drainage angle.
pressure remains constant as long as the production and absorption
of aqueous is equal.
What is glaucoma?
Glaucoma is an increase in IOP. This is measured using an instrument
called a tonometer. The cause of glaucoma is related to
inadequate drainage of aqueous rather than its over production.
Glaucoma may be primary or secondary.
glaucoma results in increased intra-ocular pressure in a healthy
eye. Some breeds are more prone than others. It occurs due to
inherited anatomical abnormalities in the drainage angle. For
example, in narrow angle glaucoma there is a shallow anterior
chamber which causes the iris to block the iridocorneal angle
interfering with the filtration. Abnormalities in the drainage angle
(goniodysgenesis) can lead to a raised IOP in middle age.
glaucoma results in increased
intra-ocular pressure due to disease or injury to the eye. This is
the most common cause of glaucoma in dogs and cats. Causes include:
resulting in debris and scar tissue blocking the drainage angle, and
severe intra-ocular infections.
Tumors which cause
physical blockage of the iridocorneal angle.
The blood clot can prevent drainage of the aqueous humor.
Damage to the lens.
Lens proteins leaking into the eye as a result of a ruptured lens
can cause a reaction which results in swelling and blockage of the
of lens. The lens falls forward and physically blocks the drainage
angle or pupil such that fluid is trapped behind the dislocated
How is glaucoma
The most common clinical signs noted
by owners are:
Ocular pain, your dog
may partially closed and rub at the eye. He may turn away as you
touch or pet the side of his head.
A watery discharge
from the eye and the dog becomes depressed.
Physical swelling and
bulging of the eyeball become obvious. The white of the eye looks
red and engorged.
The cornea or clear
part of the eye may become cloudy (usually bluish in color).
can occur very quickly unless the increased IOP is reduced.
these signs can occur very suddenly with acute glaucoma. In chronic
glaucoma they develop more slowly. They may have been present for
some time before your pet shows any signs of discomfort or clinical
Diagnosis depends upon accurate IOP measurement (tonometry) and
internal eye examination using special instruments.
Acute glaucoma is an emergency.
Sometimes referral to a
veterinary ophthalmologist is necessary.
It is important to reduce the IOP as
quickly as possible to reduce the risk of irreversible damage and
It is also important to treat any
underlying disease that may be responsible for the glaucoma.
Medical treatment often must be combined with surgery. Analgesics
are prescribed to control the pain and discomfort associated with
Veterinary ophthalmologists use various surgical techniques to
reduce intra-ocular pressure. If you have any difficulties with your
petís medications, please call us immediately.