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Dr. Frances Smith is a member of
N.T.B.T.C. and is a licensed vet in Tx. and Miss..
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HOW DRY EYE AM by
Frances Smith, DVM
Posted November 2001
Dry eye or keratoconjuntivitis sicca (KCS) is a condition of the eye
that results from a lack of tear production. Why are tears so
important? They carry nutrients and oxygen to the clear part of the
eye, the cornea. The healthy cornea has no blood vessels. If it did,
it wouldn’t be clear, so the tears are one way to nourish this important
structure of the eye. The other source of nourishment for the cornea is
the water behind it, inside the eye, called the aqueous humor. Tears
also cleanse and lubricate the cornea, help control infection, and aid
in healing when the cornea is traumatized.
Tears are made up of a three-layered film. The outer layer is the
lipid, or oily layer that keeps the next layer from evaporating. The
next layer is, you guessed it, the aqueous, or water layer that makes up
the majority of the volume of tears. The third layer is next to the eye
and is made of mucus that helps spread the tears over the cornea. KCS
occurs when there is decreased production of the water layer, increased
evaporation, or break up of the tear film. In dogs, the most common
cause is a decrease in the production of the water layer.
KCS has a number of reported causes. These include infections of the
tear glands, viral infections, hypothyroidism, and immune mediated
diseases that attack the tear glands. Certain drugs that contain sulfas
can also decrease tear production, especially if they must be used for
long periods. Much of the time a specific reason for the dryness cannot
be determined. KCS can occur in any dog but some breeds, including the
Boston Terrier, are more prone to the disease. Most of the time, KCS
requires life-long treatment to prevent blindness and to keep the eye
comfortable.
The eyes of dogs with KCS are irritated and red with lots of white to
yellow-green mucus discharge that can accumulate in the corners of the
eyes or in the hair around the eyes. Eyes that remain dry can develop
corneal ulcers, scarring, and pigmentation (darkening of the cornea).
There are a number of conditions that can look similar to KCS and things
that can occur along with it. If your dog has red eyes with discharge
you should have it checked by a veterinarian. If KCS is suspected, a
Schirmer Tear Test should be done. This is a simple test to measure the
production of the watery part of the tear film that is done by placing a
small strip of special paper between the lower eyelid and the eye. The
paper is held in place for one minute. The amount of water soaked into
the paper is compared to a scale. Normal tear production should wet the
paper at least 15mm. When there isn’t enough water present, the wetness
extends to 10mm or less. There is a “gray area” between 10 and 15mm and
treatment would depend on what other conditions are present and the
breed of the dog. In general, dogs with shallow orbits and bulgy eyes
need more tears to cover a larger area, so dry eye treatment might be
started when the values are in this “gray area”. Other tests, such as
staining the eye with a flourescein stain to check for corneal ulcers
may also be done.
KCS is most often treated medically. This is accomplished by keeping
the eye wet with artificial tears (drops and ointment) and by
stimulating tear production. Artificial tear drops must be applied very
frequently – every two hours – to successfully lubricate the eye.
Ointment lasts longer but can be messy and can interfere with the dog’s
vision. The problem with artificial tears, besides having to apply them
so frequently, is that real tears do so much more than just wet the
eye. They supply nutrition to the cornea and contain substances that
help prevent bacterial growth. So even when you can get them into dry
eyes every few hours, they often are not enough to treat this disease
alone. That’s where the tear stimulating drugs come into play.
Pilocarpine is a drug than can be given orally and directly stimulates
the glands that produce tears. Often, there isn’t enough functioning
tissue left, so this drug does not work. It also has an unpleasant side
effect of making the dog salivate a lot and can cause vomiting and
diarrhea. The current drug of choice is cyclosporine. It is packaged
and marketed for dogs by Schering-Plough-Animal Health as an ointment
called “Opptimmune”. Cyclosporine is a noncytotoxic immunosuppressive
drug long used in human medicine to help prevent organ transplant
rejection. In dogs, KCS is often caused by an immune mediated reaction
in the tear glands, so this drug may improve tear production by reducing
this reaction and allowing it to function more normally. This drug must
be administered twice a day for at least one month to see if it will
help. At the end of the first month of treatment, a Schirmer Tear test
often shows more tear production. It may take several months before the
level is normal at which time the administration can often be reduced to
once a day or sometimes every other day. The treatment MUST continue
for the rest of the dog’s life. Once the drug is stopped, the immune
mediated reaction is no longer suppressed and the tear production
decreases again. Other medical treatment could include corticosteroids
drops or ointment to reduce the inflammation if no corneal ulcer is
present, and antibiotic drops to treat corneal ulcers and bacterial
conjunctivitis.
If medical treatment is not successful, a surgical procedure can provide
relief to some dogs. This surgery is a parotid duct transposition. It
moves the outflow of the parotid salivary gland from inside the mouth to
the eye. Some problems with this procedure are that, like artificial
tears, saliva is not tears, and so does not nourish the cornea as well
as tears do. Also, saliva is not produced constantly. The dog must
often be fed small amounts every two hours to stimulate the saliva to
flow over the eye. Some dogs produce a lot of saliva that can flow down
the face and can cause dermatitis.
Most dogs with KCS can be successfully managed with medical therapy. A
few dogs may need surgical management. Whichever is indicated, it is
important to remember that this is a disease that must be continually
treated for the rest of dog’s life. Use the medications your
veterinarian prescribes faithfully. Watch the eyes carefully. If you
see more discharge or redness, have the dog checked quickly. There are
several other things that help the medications work better. The first
thing is to remove any discharge present before applying ointments or
drops. You can use an irrigating eye solution available at drug stores
to gently rinse the eyes then remove the discharge with a tissue. If it
is hard to remove, apply a warm, moist compress for a few minutes to
soften it. If you have been instructed to use drops AND ointment at the
same time, put the drops in first then wait a few minutes to apply the
ointment. It is very important to return for regular follow-up visits
to re-evaluate tear production and monitor for secondary problems.
With your veterinarian’s help, you can manage dry eyes that would
otherwise rob your dog of its vision and comfort.
Please note: The information provided here is meant to supplement that
provided by your veterinarian. Nothing can replace a complete history
and physical examination performed by your veterinarian.
November 2001
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