A cataract is an opacity that
develops in the crystalline lens of the eye or in
its envelope. Early on in the development of age-related
cataract the power of the crystalline lens may be
increased, causing near-sightedness (myopia), and
the gradual yellowing and opacification of the lens
may reduce the perception colors. Cataracts typically
progress slowly to cause vision loss and are potentially
blinding if untreated. Moreover, with time the cataract
cortex liquefies to form a milky white fluid in
a Morgagnian Cataract, and can cause severe inflammation
if the lens capsule ruptures and leaks. Untreated,
the cataract can cause phacomorphic glaucoma. Very
advanced cataracts with weak zonules are liable
to dislocation anteriorly or posteriorly. Such spontaneous
posterior dislocations (akin to the historical surgical
procedure of couching) in ancient times were regarded
as a blessing from the heavens, because it restored
some perception of light in the bilaterally affected
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.
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.
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 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.
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.
Although cataracts have no scientifically proven
prevention, it is sometimes said that wearing ultraviolet-protecting
sunglasses may slow the development of cataracts.
Regular intake of antioxidants (such as vitamin
C and E) may be helpful.