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Canine Cataracts
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Cataracts and Cataract Surgery in small Animals
Cataracts in the German Shepherd
Cataracts
Cataracts and Cataract Surgery in Small Animals
WHAT IS A CATARACT?
The lens is a unique living ocular tissue that is usually clear or
transparent and is referred to as 'the crystalline lens' by doctors.
The normal lens focuses light on the light-sensitive nervous tissue located
in the back of the eye which is known as the retina. A cataract is an opacity
(or cloudy change) of the lens that scatters light and looks gray or white.
The word cataract literally means "to break down." The word applies to
waterfalls and rapids as well as to the lens. Cataractous changes of the
lens may appear as small insignificant dots, microscopic blisters, a cracked-glass
appearance, a diffuse haze, a "pearl-like" sheen, white streaks or a completely
white lens. The cataract usually starts as small dots or microscopic blisters
and progresses to involve larger areas of the lens. The rate of progression
is difficult to predict and may be very slow or quite rapid. At times the
cataract appears to worsen overnight. Cataracts may develop in one or in
both eyes. If a large portion of the lens becomes white, it prevents formed
images from reaching the retina and blurred vision results. When a light
is shined into the eye of a patient with a complete cataract, the patient
only sees a white light and no images can be seen.
WHAT SHOULD YOU DO IF A CATARACT IS SUSPECTED?
The first thing to do if your veterinarian indicates your pet has
a cataract is to have your pet examined by a veterinary ophthalmologist.
The lens is an important link of the total visual system, yet the health
of the entire eye should be evaluated before the lens develops a complete
cataract. Early evaluation of the eye with a cataract sometimes permits
examination of the retina. If the cataract is complete and 'mature', the
retina cannot be directly examined and an ultrasound or an electroretinogram
examinations, or both may be needed to assess the health of the retina. At
the time of the initial examination, the cataract may sometimes be identified
as to cause, area of involvement and stage of progression. Not all cataracts
lead to blindness. "Incomplete" cataracts may not impair vision significantly.
If your pet has a cataract and has shown some visual loss, evaluation
will include the consideration of and benefit of cataract surgery.
HOW DO YOU KNOW IF YOUR PET HAS A VISION PROBLEM?
Animals are creatures of habit and pets love to please their owners.
If vision loss develops slowly over a long period of time, your pet may
adjust to your home and yard. Pets in familiar surroundings may readily
move about even when almost blind because they have learned where all objects
are. Signs such as bumping into objects, failing to retrieve favorite toys
and fear of being left alone may be signs of vision loss. These are especially
significant if they occur within the pet's home or yard.
WHAT CAUSES CATARACTS?
The cause of cataracts is an area continually being studied. Cataracts
may result from injuries to the eye, inflammation within the eye (uveitis),
internal diseases that have an effect on the eye such as diabetes mellitus
and some cataracts are inherited. Although it may be difficult to name
the specific cause of a cataract, cataracts that develop in eyes free
of signs of ocular disease are assumed to be inherited. Inheritance is
the major cause of cataracts in dogs and cats.
ARE THERE TYPES OF CATARACTS?
The type of cataract may not be important for deciding whether surgery
may be performed. Cataracts may be classified by age of onset (congenital,
acquired or juvenile, or senile), physical appearance of the cataract
(location in the lens -see below), state of development of the cataract
(incipient, immature, mature, hypermature or morgagnian), or cause (traumatic,
diabetic, inherited).
WHAT IS THE TREATMENT FOR CATARACTS?
There is no medical treatment known to slow the progression of, prevent
the formation of or reverse the changes of cataracts. Surgery to remove
the cataractous lens is the only known treatment in animals and man. Successful
surgery can provide a return of vision.
SHOULD MY PET HAVE CATARACT SURGERY?
Cataract surgery is generally restricted to those patients who have
developed a cataract in both eyes. If one eye has a blinding cataract and
the other eye has a rapidly developing cataract, or if rapidly developing
cataracts are present in both eyes, surgery is recommended so the patient
will not completely lose vision. It is also important to consider whether
the patient is a good candidate for anaesthesia. With continued improvements
in veterinary medicine and anaesthesia, age alone does not a limit the possibility
of surgery. With the use of modern anaesthetic agents, successful surgery
is performed on dogs and cats 17-18 years of age and older. The over-all
health of the patient needs to be assessed before surgery. This may include
chest x-rays, EKGs, blood chemistry or other procedures as recommended
by your veterinarian. Cataracts may be removed from one or both eyes during
the same surgery. Finally, you are the one who hears all the information
and decides if surgery will be performed to restore vision for your pet.
IS MY PET A GOOD CANDIDATE FOR CATARACT SURGERY?
Cataract surgery involves a period of intense pre- and post-operative
care followed by an extended period of low level therapy. If you are unable
to provide this treatment, surgery is not recommended. Alternatively, if
your pet will not or cannot be treated as required, he/she is not a good
surgical candidate. Animals who bite the hand that feeds it don't do well
after surgery.
WHAT WILL MY PET BE ABLE TO SEE AFTER SURGERY?
Patients benefit from cataract surgery because it will allow them
to be able to move about without the fear of bumping into objects. As in
people, the loss of the lens causes a loss of up-close visual acuity or
sharpness. Without a lens, a pet may not have completely normal vision
after surgery, but they do regain some vision. The image they see will
be slightly larger and only partially focused so that the images will be
much less distinct. Although our pets don't drive, play golf or tennis
they need sharp vision yet it is not as necessary as for humans. Most veterinary
patients are handicapped without a lens yet others do not show significant
vision loss. Veterinary ophthalmology has learned much from the ophthalmic
physician and we know that most dogs will see much better when an artificial
lens is implanted inside the lens capsule. We do this procedure when the
client requests it and the surgery allows it to be done. The estimate you
receive before the surgical procedure will have the option of lens implantation.
WHAT DOES CATARACT SURGERY INVOLVE?
Cataract surgery is performed on an outpatient basis by many veterinary
ophthalmologists, while others will admit the patient for one or two days.
The patient is admitted to the hospital the morning of surgery and an intravenous
catheter is placed to facilitate the administration of drugs. Drops are
placed in the eyes at specific intervals before surgery. General anaesthetic
is induced using the most modern agents. An ultrasound may be performed
to examine structures inside the eye that cannot be visually seen. An electroretinogram
[ERG] is performed to determine that there is a reasonable chance for vision
following surgery. This procedure is used if the cataract has progressed
to the point that the ophthalmologist cannot assess the retina during the
initial examination. If the ERG indicates that vision is not possible, then
surgery is not performed and the patient is awakened. If the ERG shows that
vision is possible, the patient is prepared for surgery and moved to the
surgical centre. During the surgical procedure, the surgical technician
will monitor the pet’s respiration and heart rate. An EKG will be attached
to your pet so that the heart can be assessed while the patient is undergoing
surgery. Surgery is performed using an operating microscope and sophisticated
microsurgical instruments. The actual surgical procedure may last 30-40
minutes and general anaesthetic is normally for 60-120 minutes. The cataract
is removed by a technique known as phacoemulsification. The eye is entered
with a small incision, the lens capsule is carefully opened in a technique
called capsulotomy, and the lens is removed by the phaco instrument which
emulsifies the lens into a mulch with ultrasonic waves, and aspirates the
remnants. This is the same technique that is used in human cataract surgery.
Although lasers are not involved in this procedure, it has become common
lingo amongst people who have had cataract surgery by phacoemulsification
to say that their cataract was removed by the laser.
During recovery, your pet will be closely monitored. An Elizabethan
collar (E-collar) is placed on the pet so they will not injure their own
eyes during the first 7 to 14 days following surgery. Postoperative medications
are used to reduce inflammation and preventing infection and are given
every 6 hours for the first 24 hours.
The first postoperative examination is scheduled for the afternoon
the day following surgery. During that examination, the pressure within
the eye will be examined, the eye is evaluated for inflammation and determination
of possibility of infection will be made.
WHAT ARE THE COMPLICATIONS OF CATARACT SURGERY?
The success rate in cataract surgery has improved markedly in the
recent years with the advent of newer medications and microsurgical techniques.
Although the success rate has risen dramatically,
there are still several complications that need to be anticipated
to prevent them. Intraocular bleeding, elevation of intraocular pressures
[glaucoma], extreme postoperative inflammatory response, retinal detachment,
adhesions and self-trauma are possible complications. The risk of anaesthesia
is extremely minimal. The risk associated with surgery will be explained
to you before the surgery being scheduled.
Cataracts
in the German Shepherd
Fred Lanting
Copyright 1998
Cataracts - This is a disorder of that part of the eye that
looks like the double-convex glass disk in the telescope, binocular, microscope,
magnifying glass, etc. The lens is clear and transparent in the normal
dog, is filled with a viscous fluid, and is situated between the outer
"skin-like" cornea and the main part of the eyeball containing the vitreous
humor, another fluid. At the back of the eye, the retina is the site of
a shallow depression where images focused by the lens are received and transformed
into electrical impulses carried by the optic nerve to the brain, where
they are interpreted. The word cataract is used for any cloudiness or opacity
of the lens and in some dogs, especially Labrador Retrievers and Samoyeds,
it occurs secondary to Progressive Retinal Atrophy (PRA). Although rare,
cataract in German Shepherds is believed to be due to a recessive gene;
in a few dogs it results from a different, dominant gene. True cataracts
may not be detected simply because some are minor, and a dog doesn't need
reading ability vision to get around and doesn't complain about things
looking dim or fuzzy. If you suspect cataracts in an old dog you are probably
wrong; the bluish colour beyond the pupil and lens is seldom a true cataract,
but rather the normal result of old age. There is opacity that is occasionally
found on the lens, which may be diagnosed as a cataract by a non-ophthalmologist,
and that is called fibrillar nuclear opacity. There are a number of terms
that overlap in meaning and may be confusing to the dog owner. Some are
hardly noticeable, some may cause total blindness, others somewhere in
between in severity. Further complicating the picture is the fact that
some cataracts are definitely hereditary, some are acquired, some noticed
early, some not identified at first, some late-onset. Location, progression,
and other descriptions run the gamut in size, type, permanence, and other
characteristics. Congenital means present from birth (usually though not
absolutely always inherited) even though many owners don't see the lesion
until the dogs and their eyes are larger. "Juvenile" cataracts (a misnomer)
might not start until as late as six years of age. Juvenile cataracts are
also referred to as "developmental" cataracts. In the German Shepherd Dog,
most cataracts are the congenital, progressive, and autosomal-recessive
type. That latter term means it is not linked with the gene determining
gender, so it will affect and be carried by either sex; it also means that
both parents must be carriers (or afflicted, of course, though that's not
likely). In Chessies and Goldens, a dominant gene causes cataracts, so it's
a bit easier to “cull the culprits.” Juvenile cataracts may be the same as
congenital, depending on how closely the eye is examined, so if the term
is used in connection with a GSD, you might best consider it to be the inherited,
congenital form, especially if it gets worse with time.
In the GSD, at least, it is hard to differentiate acquired from congenital
cataracts. The possible environmental causes are many: nutritional/metabolic,
exposure to toxins, inflammation associated with disease organisms, and
trauma, mostly. Diabetes, DMSO ("horse" liniment), and DNP (a formerly popular
injectable wormer) are others. They may be progressive, too, but are less
likely to be so than is the certain worsening within a year of the inherited/congenital
type. Orphan pups on a milk replacer sometimes develop cataracts, probably
due to an arginine amino acid deficiency; just add a little powdered gelatin
to the formula to reduce risk. Often, acquired cataracts are reversible
by removing the causative agent.
Other opacities may appear on the cornea over the pupil or slightly
off-center, and the novice might think the dog has cataracts. For example,
an allergic reaction or some other cause may show up as a small spot,
the opacity varying from slightly translucent to more white. The size
is usually less than 5mm across, round, oval, or horseshoe-shaped. Most
eye specialists refer to this type of opacity as "corneal dystrophy"; the
spots do not interfere with vision. In my experience the spots have faded
away in a few years after reaching maximum size. Corneal dystrophy appears
to be genetic, but is not serious. Probably less than one percent of the
breed is affected. I once had a bitch that developed very small oval opacities,
one on each cornea, after she was about four or five years old. They finally
and gradually disappeared (shrunk to nothingness) by the time she was about
ten years or more. At least one of her sons had the same condition, appearing
in maturity and going away without treatment by old age. This bitch also
developed atopic (allergic-type) problems marked by itching feet and sometimes
parts of the skin, but most noticeably by an assumed feeling of excess phlegm
in the throat. To get rid of this mucus, she would eat "scratchy" nonfoods
such as dried pine needles, bark, sand, fabric (on hidden parts of furniture)
and even fibreglass curtains. I had to administer about 1-2ml of prednisone
every 4 weeks to control this "itch" and to keep her from extreme discomfort
and destructive/unwanted behaviour; a month was too long, and I mistrust
steroids enough that any more frequently was undesirable. The steroids almost
undoubtedly contributed to her sudden death, probably of mesenteric capillary
hemorrhage, about six weeks following an operation for gastric torsion
when she was 12 years old. One of her many sons developed the same transient
and minor corneal defects.
Copyright, Fred Lanting, 1998. Reprints, forwarding,
website or magazine use must have the author's permission in writing (e-mail
approval OK). Send complete description of proposed use and medium to:mailto:Mr.GSD@juno.com Fred Lanting,
"All Things Canine" Consulting, behaviour analysis, evaluations, seminars,
Lectures; Author, "The Total GSD", "Canine HD"
Reprinted with kind permission of Fred Lanting Author of The Total German Shepherd
Dog
This
is the expanded and enlarged second edition, a "must" for every true
GSD lover. It is an excellent alternative to the "genetic history" by
Willis, but less technical and therefore suitable for the novice, yet
very detailed to be indispensable for the reputable GSD breeder. Chapters
include: History and Origins, Modern Bloodlines, The Standard, Anatomy,
The German Shepherd in Motion, Shows, Showing, and Training, The Winners,
Nutrition and Feeding, General Care and Information, Health and First
Aid, Parasites and Immunity, Diseases and Disorders, The Geriatric German
Shepherd, Breeding, Basics of Genetics, Reproduction, Whelping, The First
Three Weeks, Four to Twelve Weeks, Trouble-shooting Guide
Permission
to reprint this article may only be given by the author Fred
Lanting
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Cataracts
The normal lens of the eye
is a focussing device. It is completely clear and is
suspended in position by tissue fibers called zonules just inside
the pupil. The lens focuses an image on the retina in the back of the
eye in a process called accommodation. The focussing power of the dog's
lens is at least three times weaker than that of a human and a cat's lens
is at best half the focussing power as a human's. (It is helpful to remember
that dogs and cats have a sense of smell at least 1000 times more accurate
than ours and this is their primary means of perceiving the world.)
Despite its clarity, the lens is in fact made of tissue fibers. As
the animal ages, the lens cannot change its size and grow larger; instead,
it becomes more compact with fibers. This condition is called nuclear sclerosis
and is responsible for the cloudy-eyed appearance of older dogs but these
lenses are still clear and the dog can still see through them; these are
not cataracts. The lens is enclosed in a capsule that, if disrupted, allows
the immune system to see the lens proteins for the first time, recognize
them as foreign, and attack. The resulting inflammation is painful and
can be damaging to the eye.
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A cataract is an opacity in the lens.
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Cataracts can be congenital, age-related, of genetic origin (the most
common cause), caused by trauma, by dietary deficiency (some kitten milk
replacement formulas have been implicated), by electric shock, or by toxin.
The patient with a cataract is not able to see through the opacity. If the
entire lens is involved, the eye will be blind.
A Special Note On Diabetes Mellitus In Dogs
Many things can cause the lens to develop a cataract. A special cause
is diabetes mellitus. In this condition the blood sugar soars, as does the
sugar level of the eye fluids. The fluid of the eye's anterior chamber
(see illustration above) is the fluid that normally nurtures the lens
but in the diabetic pet the lens can only utilize so much sugar. Excess
absorbed sugar is transformed into sorbitol within the lens, which unfortunately
draws water into the lens causing an irreversible cataract in each eye.
Cataracts are unavoidable in diabetic dogs no matter how good the insulin
regulation is; diabetic cats have alternative sugar metabolism in the eye
and do not get cataracts.
What Else Could it Be?
Many owners are not really able to tell which portion of the eye looks
cloudy. Cloudiness on the cornea, as caused by other eye diseases, can
be mistaken for a cataract by an inexperienced owner. Also, in dogs, the
lens will become cloudy with age as more and more fibers are laid down
as described above. Nuclear sclerosis can mimic the appearance of a cataract,
yet the eye with this condition can see and is not diseased. It is a good
idea to have your veterinarian examine your pet if you think he or she
has a cataract, as you could be mistaken.
Why Is Having a Cataract Bad?
The area of the lens involved by the cataract amounts to a spot that
the cannot be seen through. If the cataract involves too much of the lens,
the animal may be blind in that eye and, of course, there could be cataracts
in both eyes which means the pet could be rendered completely blind.
A cataract can luxate, which means that it can slip from the tissue
strands that hold it in place. The cataractous lens can thus end up floating
around in the eye where it can cause damage. If it settles so as to block
the natural fluid drainage of the eye, glaucoma (a build up in eye pressure)
can result, leading to pain and permanent blindness. A cataract can also
cause glaucoma when it absorbs fluid and swells so as to partially obstruct
fluid drainage from the eye.
Cataracts can begin to dissolve after they have been present long enough.
This sounds like it could be a good thing but in fact, this is a highly
inflammatory process. The deep inflammation in the eye creates a condition
called uveitis, which is in itself painful and can lead to glaucoma.
A small cataract that does not restrict vision is probably not significant.
A more complete cataract may warrant treatment. Cataracts have different
behavior depending on their origin. If a cataract is of a type that can
be expected to progress rapidly (such as the hereditary cataracts of young
cocker spaniels) it may be of benefit to pursue treatment when the cataract
is smaller and softer, as surgery will be easier.
What Treatment Is Available?
Cataract treatment generally involves surgical removal or physical
dissolution of the cataract under anesthesia. This is invasive and expensive
and is not considered unless it can restore vision. A complete examination
of the eye is performed by a veterinary ophthalmologist. If a cataract
is present, it is not possible to see the retina through it; a test called
an electroretinogram is done to determine if the eye has a functional
retina and could benefit from cataract surgery. Ultrasound of the eye
can be used to look for retinal detachments. If the eye has a blinded
retina, there is no point to subjecting the patient to surgery.
Obviously, the patient must be in good general health to undergo surgery;
diabetics must be well regulated before cataract surgery. Also, it should
be obvious that in order for a patient to be a good candidate for surgery,
the patient must have a temperament conducive to the administration of
eye drops at home. Pets with cataracts in one eye that can see in the other
eye generally do not need surgery.
If the patient proves to be an appropriate surgical candidate, the
lens can be softened and sucked away using a technique called phacoemulsification.
If the patient is relatively young, the lens is relatively soft and phacoemulsification
is the first choice procedure.
Older patients have much harder lenses and it is more common in these
patients to simply remove the lens surgically.
Complications
Some degree of uveitis (deep inflammation) is unavoidable. This can
cause a pupil constriction reaction that can increase the risk to scarring
within the eye. Eye drops to keep the pupil dilated are usually effective
in preventing this but not always. Inflammation in the eye will resolve
over weeks to months after surgery. Success rate is higher for cataract surgery
if minimal inflammation is present in the eye prior to surgery thus pre-operative
anti-inflammatory eye drops are frequently prescribed.
Another complication involves the development of opacities on the remaining
lens capsule. In humans, laser surgery is used to remove the lens capsule
but in dogs, the capsule is too thick for this. Some ophthalmologists
prefer to remove the capsule as a preventive measure. The portion of the
capsule that is involved in this reaction is present in young dogs but
not in adult dogs.
Bleeding after surgery can be an enormous complication and can easily
be caused by excess barking or activity after surgery. Small bleeds are
of little consequence but a large bleed could ruin vision.
Overall, a 90% success rate is described after cataract surgery.
An Elizabethan collar will be very important after surgery, as patient
rubbing or pawing at the eye could be a disaster. Topical therapy (eye
drops) will be needed for several months after surgery.
Before embarking on the adventure of cataract surgery, be sure to obtain
a clear explanation from your ophthalmologist of exactly what the home
care will involve.
Lens Implantation
A prosthetic lens may or may not be inserted after the cataractous
lens has been removed. Without the prosthesis, the dog's vision will be
approximately 20/800, and objects will appear to be reversed (as in a
mirror). This sounds debilitating but, again, it is important to remember
that pets do not depend on their eyes in the way we do so it is hard to
make a good analogy.
Pros: A prosthetic lens allows for normal restoration of vision.
Cons: The incidence of uveitis (deep eye inflammation) after
surgery is increased for patients receiving lens implants. Dogs appear to
have functional vision without prosthetic lenses. In one study, the complication
rate was 15% after lens implantation.
What if it Goes Untreated?
A cataract by itself does not necessarily require treatment. If there
is no associated inflammation and no associated glaucoma and the only problem
is blindness, it is perfectly reasonable to have a blind pet. Blind animals
have good life quality and do well though it is important not to move
furniture around or leave any hazardous clutter in the home.
Copyright
2001 - 2007 by the Veterinary Information Network, Inc. All rights reserved.
This work was originally published by Veterinary Information Network,
Inc. (VIN)
and is republished with VIN's permission.
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The above information is simply informational.
It's intent is not to replace the advice of a veterinarian nor to assist
you in making a diagnosis of your pet. Please consult with your own veterinarian
for confirmation of any diagnosis. Your pets life may depend on it.
