Glaucoma is a serious eye
disease that often leads to blindness. There is a
continuous (although very slow) exchange of fluid between the chambers of the
eye and the systemic venous circulation. Fluid in the eye is produced by the
ciliary body and leaves the eye at the angle formed by the iris and the cornea. Glaucoma occurs when
fluid in the eye is produced faster than it can be removed. This leads to a
sustained increase in intraocular pressure. High intraocular pressure causes
degenerative changes to the optic nerve and the retina. Glaucoma is described
as primary or secondary.
Primary glaucoma is a hereditary disease that affects Beagles, Cocker
Spaniels, Basset Hounds, Samoyeds, and other breeds. In 50 percent of cases the
second eye is involved within two years of the first.
Diabetes mellitus, sometimes called sugar diabetes, is
a common disease in dogs. Golden Retrievers, German
Shepherd Dogs, Miniature Schnauzers, Keeshonden, and Poodles have the highest
incidence, but all breeds can be affected. Females with the disease outnumber
males by three to one. The average age of onset is 6 to 9 years.
Diabetes is a result of inadequate production of insulin by the islet cells
in the pancreas. There may be a genetic predisposition for this in some dogs.
Secondary glaucoma is a complication of another eye disease such as uveitis, displacement of the
lens, or trauma to the eye. Treatment of secondary glaucoma is directed toward
the underlying eye problem.
Glaucoma may also be acute or chronic, depending on how quickly the signs
develop and how long the glaucoma has been present. An eye with acute glaucoma
is exquisitely painful, with tearing and squinting. The affected eye feels
harder than the normal eye and has a fixed, blank look due to the hazy and
steamy appearance of the cornea and enlarged pupil.
Glaucoma in the chronic stage is associated with enlargement of the globe
and protrusion of the eyeball. The eye may be tender to pressure and feel
harder than the unaffected eye. In nearly all cases the affected eye is
The diagnosis of glaucoma can be made only by a veterinary eye examination
and measurement of intraocular pressure.
Treatment: Acute glaucoma is a veterinary emergency that can produce
blindness in a matter of hours. This is one reason why it is so important to
take your dog to a veterinary hospital
immediately on suspicion of a painful eye. Medical treatment involves the use
of drugs to rapidly lower intraocular pressure.
The initial drug of choice has been intravenous mannitol. Other
veterinarians will start with prostaglandins, such as Xalatan, and give
carbonic anhydrase inhibitors orally. Mannitol increases serum osmotic pressure
and draws fluid out of the anterior chamber into the circulatory system. Other
drugs used in treating glaucoma include carbonic anhydrase inhibitors that
block the enzyme that produces the intraocular fluid. Topical medications
increase outflow of fluid by constricting the pupil. This widens the angle
between the iris and the cornea.
If medical treatment is not effective, a surgical procedure such as
cyclodestructive surgery or filtering surgery may be done. These reduce fluid
production in the eye. Some veterinarians use cryosurgery, which involves
freezing and destroying a portion of the ciliary body to reduce the production
of intraocular fluid. The operation can also be done with a laser, but this
requires referral to a special canine eye center.