|Note: I originally wrote this article for a National Samoyed publication, but the information applies to most breeds as well, so I hope it will be helpful here.|
GLAUCOMA IN THE SAMOYED
(and other breeds)
by Kerry Meydam
Samoyed is one of those breeds considered to have a significant
incidence of glaucoma, we should be familiar with what it is, how to
recognize it, and what can be done for it. One of the primary problems
in dealing with glaucoma in dogs is the difficulty in diagnosing the
disease in the early stages, when the prognosis for retention of sight
is most favorable. It is frequently misdiagnosed in the early stages and
is most frequently identified only after irreversible changes in the eye
have led to a total irreversible loss of vision, frequently accompanied
by an eye that is painful and cosmetically unacceptable. If you know
that this is a problem in our breed, and you can recognize what might be
the early signs of glaucoma in your dog, you may be able to help your
veterinarian by requesting that he measure IOP (intraocular pressure) on
your dog, or you may have the benefit of a veterinary ophthalmologist
near by who is available on an emergency basis, which glaucoma certainly
is (an emergency).
In this article, I will try to describe the signs, testing, treatments available, and how your dog can be tested for an abnormality which predisposes him to glaucoma, which is not covered in your CERF exam, but does occur at a significant rate in our breed.
speaking, there are 2 classifications of glaucoma - Primary and Secondary.
Primary glaucoma occurs without previous trauma or ocular
disease, and will eventually affect both eyes.
Secondary glaucoma is a consequence of some other disease, such
as ocular inflammation, lens dislocation, intraocular tumors, or trauma.
glaucoma is known to occur in certain breeds at a significant rate and
is thought to have a genetic basis - it may be familial or
hereditary. At the present time there is no proof that it is inherited
in the Samoyed, although with more study and more information compiled
in the future, we may find that this is the case.
are 3 basic types of glaucoma: Open
angle glaucoma as seen in Beagles, Norwegian Elkhounds, Miniature
poodles, and sometimes the Basset Hound; Narrow angle glaucoma as seen
in American and English Cockers and the Basset Hound; Mesodermal
Dysgenesis, or Goniodysgenesis, as seen in the Samoyed and Basset Hound.
(The Samoyed may also have narrow angle glaucoma, or a
combination of both).
is the increased pressure inside the eye due to a decrease in aqueous
humor outflow. [See the diagram and glossary of terms] Aqueous humor is
produced by the ciliary body cells and is secreted into the posterior
chamber of the eye. It
flows over the anterior surface of the lens, through the pupil and into
the anterior chamber. The fluid exits through the flow holes in the
pectinate ligament. The
area of aqueous outflow, the iridocorneal angle, may be examined
clinically with a corneal contact lens. Next, the aqueous humor is
resorbed into the bloodstream. (See diagram)
A delicate balance between production and resorption maintains
the normal intraocular pressure. The production of aqueous humor is not
regulated by the intraocular pressure, however. Occlusion (blockage) of
the primary outflow pathway, either at the pupil or iridocorneal angle,
results in increased IOP (glaucoma).
In the embryo, the iridocorneal angle is a smooth, closed sheet
of tissue. Late in
gestation and continuing in the early postnatal stage, the tissue
undergoes progressive rarefaction (becomes less dense, more porous,
thinner), and leaves a sheet of tissue now consisting of fine fibers
(ligaments) with flow spaces between them. The pectinate ligament spans
the area between the base of the iris and the sclera (white part of the
eye). In some dogs, the pectinate ligament does not undergo enough
rarefaction to form normal pectinate ligaments and flow spaces. This
arrest in the development of the angle may occur as long as perhaps
three weeks after birth. What results in some cases, is a broad sheet of
tissue with few openings, which impedes the outflow of aqueous humor.
Most animals have rather long slender strands making up the pectinate
ligament. These strands occasionally branch and join adjacent strands,
and some animals have rather stout ligaments that are often
correspondingly short. This shortness may be associated with a webbing
of iridal tissue between strands that bridge the width of the angle from
1/3 to 1/2 the width. Extreme examples of this may be associated with
glaucoma. Goniodysgenesis signals a potential pre-glaucoma anatomy.
The classical signs of glaucoma, which are often signs of
advanced glaucoma, include: episcleral
congestion, or a "red eye", due to resistance to venous flow
and veins become dilated; megaloglobus,
or enlargement of the eye, which is a sign of advanced and usually
chronic glaucoma (although a young dog with less scleral rigidity may
show enlarged globes earlier than older dogs);
the eyelid may not be able to completely close over the enlarged
eye, sometimes resulting in corneal ulceration. Most veterinarians will
recognize glaucoma at this stage, although by this time, vision is
permanently lost. Dislocation of the lens may also occur at this time
due to stretching of the fibers which hold it in place.
signs of glaucoma:
The early signs of glaucoma, which may not be recognized as such,
may consist of mild conjunctival inflammation, which can mimic
conjunctivitis; increased tearing and pain; and photophobia (sensitivity
to light which results in some "squinting" of the eye). Visual
impairment is rarely observed at this stage, even when both eyes are
involved. The cornea begins to become cloudy as well. The general
practitioner is not always aware of the early signs or of the
predisposed breeds, and that is where we can be of help, by requesting
that he/she measure IOP (intraocular pressure) as a part of the
examination of the eye. If IOP is elevated above 50 mm Hg, corneal edema
(cloudiness), inflammation, and a dilated fixed pupil are
characteristic. Normal IOP ranges from 15 to 25 or 30 mm Hg (20 or below
is preferred). If IOP is 30 to 50 mm Hg, the pupil may be moderately dilated
and have a sluggish reaction to light.
|The diagram below shows the anatomy of the eye concentrating on the drainage angle and its relationship to the cornea and lens, and the direction of aqueous outflow from the ciliary body to the aqueous vein.|
The watery fluid present in the anterior chamber of the eye.
of the iridocorneal angle and pectinate ligaments with a special optical
ophthalmologists will have an "applanation" tonometer or
TonoPen. Following topical anesthesia (eye drops), a small probe is
applied to the center of the cornea with a gentle tapping motion, so the
probe contacts the cornea for only a fraction of a second. The contact
probe converts IOP into an electrical signal which causes a recording to
be made on paper, which is then read to determine IOP.
This method will give the most accurate reading.
The other method, digital palpation is at best crude and
unreliable. Instrumental tonometry should always be used.
of glaucoma: There is not
really an absolute "cure" for primary glaucoma. And it is
extremely important to keep in mind that primary glaucoma is a bilateral
disease. When an animal has
one eye affected, you must be aware that a similar episode is likely to
occur in the other eye (usually anywhere from 6 months to 2 years
later). Preventive medical
management may be called for in the "good" eye as well.
are several different forms of medical management, including the use of
several different types of eye drops which have different modes of
action, either to decrease the production of aqueous humor within the
eye, or to increase the outflow, or both. I won't go into all the
different types; frequently
several are used together. Topical and systemic ocular hypotensive
medications usually are not effective in controlling IOP in the dog over
extended periods of time, and many times surgical management of the
glaucoma is required. A variety of surgical procedures have been
developed to aid in the control of IOP or for cosmetic reasons in a
non-visual eye. Cyclocryosurgery and Laser Cyclophotocoagulation
relatively non-invasive techniques used on eyes to try to
save vision. This involves freezing or destruction of the
aqueous-producing ciliary body tissue in several locations, which
reduces the IOP. An Anterior Chamber Shunt is a surgical procedure where
a small valve-like device is implanted just under the surface of the
white of the eye. This device has a small tube which enters the eye
through a tiny incision and this tube provides an alternate drainage
pathway for the aqueous fluid to leave the eye. While some
ophthalmologists report frustration with this technique since the little
tube may become blocked with fibrin, or the functioning of the valve may
be compromised by scarring, other ophthalmologists report considerable
success with the procedure. In certain situations, a laser procedure AND
the implantation of a glaucoma valve is indicated.
non-visual eye may be injected with an antibiotic compound that
will reduce pressure by destroying the ciliary body, but this compound
is also toxic to the retina and is only used for irreversibly blind and
painful eyes. Sometimes the
eye must be removed (enucleation), or an intraocular prosthesis may be
placed inside the eviscerated globe to provide a cosmetic, pain free eye
usually with minimal complications.
Prognosis is largely dependent
upon how early the glaucoma is detected.
Usually the dog is presented to the veterinarian long after any
restoration of vision is possible. At this point the goal becomes a pain
free and cosmetic affected eye and preventing glaucoma in the
"good" eye, which will probably become affected from 6 months
to 2 years after the first eye. Glaucoma requires long term management
including proper medical and/or surgical therapy and regular and consistent
Does your dog have a normal Iridocorneal Angle? How do you know? The GONIOSCOPY. It is recommended that Samoyed owners have their dogs tested for goniodysgenesis and/or narrow angles. This test is NOT part of the CERF exam, but can easily be done in conjunction with it, if requested. (note: I would also recommend that owners of other breeds who are at higher risk for glaucoma do the same - Basset Hounds, Cocker Spaniels, Beagles, etc.)
is a technique used to
evaluate the iridocorneal angle, which will determine the etiology of a
glaucoma or predisposition for glaucoma. Both eyes should always be done
The test takes about 15 minutes and involves placing a
dome-shaped contact lens (goniolens) on the cornea. This lens
permits the ophthalmologist to directly view the drainage angle and
determine if the dog has goniodysgenesis, a narrow angle, etc. Either
will signal a predisposition for glaucoma.
Medical therapy may then be initiated to prevent or reduce risk
of future problems, and you may want to re-evaluate your breeding
plans for that dog if the angle is not normal.
gonioscopic examination can be performed with the use of only a topical
anesthetic, and can be done in conjunction with your CERF exam at a
regular club eye clinic if requested in advance and there is sufficient
time for scheduling. If you request a gonioscopy and the club holding
the eye clinic doesn't know anything about it, ask them to contact the
ophthalmologist who will be doing the clinic for information re:
price, scheduling, etc. Remember that the gonioscopic exam must
be done prior to the drops to dilate the pupils for the CERF exam being
administered to your dog.
gonioscopy does NOT have to be repeated yearly like the CERF exam.
Samoyeds may be done as early as 6 months of age, if the eye is large
enough for the goniolens. Or it may be done at any age after that.
Glaucoma remains a leading cause of blindness in animals. It is a
treatable disease that may be held in check with medicine, surgery or
both. Most important, it requires careful and prompt professional
attention and client understanding. Your veterinary ophthalmologist
teamed with your regular veterinarian can recommend appropriate
therapies suitable for your dog and for your situation. I highly
recommend you have all your dogs checked with a gonioscopic examination
as well as your regular CERF exam. Don't be afraid to ask your
veterinarian or veterinary ophthalmologist as many questions as you can
a few more interesting facts about glaucoma:
Glaucoma occurs more frequently in northern regions and episodes of
glaucoma occur more frequently during winter months.
The left eye is the first to be affected in approximately two thirds of
The disease is nearly three times more frequent in bitches than in dogs.
The incidence of goniodysgenesis appears to be greater in Bassets,
Samoyeds, Siberians, Chows, American & English Cockers and Poodles
than in other breeds. Open angle glaucoma is seen in Beagles and
Norwegian Elkhounds. Narrow angle glaucoma is most frequently seen in
American & English Cockers.
Glaucoma can be precipitated by immune-mediated eye diseases, such
Average age for glaucoma in the Samoyed is between 2 and 5 years of age.
The second eye is usually affected from 5 months to two years after the
would like to thank Melanie, Sue, and Mike (see references) for all
their help and patience in answering all my many questions.
copyright February 2000 Kerry Meydam