Cataracts
Joe Bodewes, DVM
Veterinary Services Department, Drs. Foster & Smith, Inc.
Cataracts are one of the most common problems affecting the eyes of
the dog. There are many different forms and causes of cataract formation.
They affect all breeds and ages of dogs but certain types show up more
commonly in certain breeds. Despite the fact that they are very common
there is still a lot that we don't know about canine cataracts. The only
current treatment option is surgery but with correct patient selection
the outcome is very good. This article will explain some of the different
forms of cataracts including their age of onset and their treatment
What are cataracts?
The word cataract literally means ‘to break down’. This breakdown refers
to the disruption of the normal arrangement of the lens fibers or its capsule.
This disruption results in the loss of transparency and the resultant reduction
in vision. Cataracts often appear to have a white or crushed ice appearance
and are found in the lens of the eye. |
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Nuclear sclerosis
I often get people that bring an older dog into the clinic complaining
of cataract formation in their dog’s eyes. The vast majority of the time
the dog does not have cataracts but has the much more common condition
known as nuclear sclerosis. Nuclear sclerosis is a normal change that occurs
in the lens of older dogs. Nuclear sclerosis appears as a slight graying
of the lens. It usually occurs in both eyes at the same time and occurs
in most dogs over six years of age. The loss of transparency occurs because
of compression of the linear fibers in the lens. The condition does not
significantly affect the vision of the dog and treatment is not recommended.
How do cataracts form?
Despite the fact that there are several different forms and causes of
cataracts, they all develop in a similar fashion. The normal lens is maintained
in a dehydrated state. It consists of 66% water and 33% protein. There
is a complicated sodium water pump system in the lens that keeps this water/protein
balance in check. When the biomechanical system in the lens is damaged,
this pump system begins to fail and extra water moves into the lens. In
addition, the percentage of insoluble protein increases. These changes
result in the loss of transparency and cataract formation.
Age of onset
The age at which a dog develops cataracts is very important in classifying
the
type of cataract. The age of onset is particularly important for determining
if the cataracts are the result of a hereditary trait in certain breeds
of dogs.
Congenital Cataracts: These are cataracts that are present at
birth. These cataracts usually occur in both eyes. Despite the fact that
the animal is born with them they are not necessarily inherited. Infections
or toxins may cause the formation of these cataracts while the puppies
are still in utero. Primary congenital cataracts such as those found in
miniature schnauzers are, however, inherited.
Developmental (Early Onset) Cataracts: Developmental cataracts
are those that develop early on in life. As with congenital cataracts they
may be inherited or caused by outside sources such as trauma, diabetes
mellitus, infection, or toxicity. Inherited cataracts at this age are
more common in several breeds including afghan hounds and standard poodles.
Senile (Late Onset) Cataracts: The cataracts that occur in dogs
over 6 years of age are called senile cataracts. They occur much less frequently
in dogs than in humans. Nuclear sclerosis, which is not considered to be
a medical problem, is often confused with cataracts at this age.
Inherited cataracts
Inherited cataracts in the dog may occur independently or in association
with other ocular disease. The breeds that appear to develop inherited
cataracts along with their age of onset are listed below. If a dog is diagnosed
with inherited cataracts, the dog should obviously not be used for breeding
because of the likelihood perpetuating the disease in the offspring.
| Breed |
Age of Onset |
| Afghan Hound |
6-12 months |
| American Cocker Spaniel |
6 + months |
| Boston Terrier |
Congenital |
| Chesapeake Bay retriever |
1 + years |
| German Shepherd |
8 + weeks |
| Golden Retriever |
6+ months |
| Labrador Retriever |
6+ months |
| Miniature Schnauzer |
Congenital or 6+ months |
| Old English Sheepdog |
Congenital |
| Siberian Husky |
6 + months |
| Staffordshire Bull Terrier |
6 + months |
| Standard Poodle |
1 + year |
| Welsh Springer Spaniel |
Congenital |
| West Highland White Terrier |
Congenital |
The most common metabolic disorder resulting in cataract formation in
the dog is diabetes mellitus. If diabetic dogs are followed for
a year or more, almost all of them would develop cataracts. In diabetic
dogs the glucose concentrations in the lens increases. The extra glucose
is converted into sorbitol, which causes an increase in the influx of water
to the lens. The increase in water causes a breakdown of the lens fibers
and a resulting cataract. Cataracts in diabetic dogs can develop extremely
rapidly if the dog is not regulated. They generally affect both eyes. Surgical
removal of the lens can be successfully performed in the diabetic dog if
the animal has been regulated successfully for at least three months.
Trauma
Trauma from an automobile accident, or penetration of a thorn, shotgun
pellet or other object may damage the lens and a cataract may develop.
These types of cataracts usually only occur in one eye and can be treated
successfully with surgical removal.
Treatment
Treatment for canine cataracts consists of surgical removal of the lens.
There is currently no good non-surgical treatment for this condition. With
the increase in veterinary surgical skill and equipment, the surgical procedure
to remove the problem lens is becoming increasingly more common. There
are several different techniques used to remove the affected lens including;
the removal of the entire lens and surrounding capsule, the removal of
the lens leaving the surrounding capsule, phacoemulsification of the lens,
and aspiration and dessication of the lens. All of these techniques can
offer excellent results. For a successful outcome the affected animal must
undergo a thorough examination to determine if it is a good surgical candidate.
Diabetic animals that are not regulated, aggressive animals that are difficult
to treat daily, or animals in poor or failing health, are not good surgical
candidates. If you suspect your dog is developing cataracts then you should
work closely with a veterinary ophthalmologist to take the best and most
effective course of treatment for the dog.
References
Gelatt. Veterinary Ophthalmology. Lea & Febiger. Malvern, PA; 1991.
Slatter, D. Fundamentals of Veterinary Ophthalmology. Saunders. Philadelphia,
PA; 1990.
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© 2001 Drs. Foster & Smith, Inc.
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