Dry eye (Keratoconjuncitivitis sicca or KCS)
Dry eye occurs when either the tear ducts do not make enough tears or they become blocked.
Symptoms of dry eye
The eyes look dull and dry, instead of having the normal shiny glistening bright look.
There will usually be thick stringy mucous-looking discharge. This can also seen in conjunctivitis. To complicate matters, episodes of conjunctivitis are common in dogs with dry eye. Sometimes a dog will be treated for conjunctivitis and not show any improvement, since the underlying problem is dry eye.
Conjunctivitis is common, since bacteria, dust, etc that get into the eye are not efficiently flushed away due to the reduced tear volume.
The most common cause of dry eye is autoimmune. The immune system of a dog attacks something in the tear duct. This damages and shrinks the tear gland. The result is that the tear gland is not releasing as much tear into the eye. The autoimmune response can be specific to the tear duct or part of a wider immune-mediated condition such as rheumatoid arthritis.
Injury to certain parts of the eye and around the eye can result in dry eye. This can include direct damage to the tear ducts, or damage to the nerves that control the tear ducts, eye infections, some diseases or occasionally a drug.
Diseases that can damage tear glands include Addison’s disease and distemper.
Infection of the eye and the middle ear can affect tear ducts. Infections in the eye can either damage the tear ducts or can cause them to become blocked. Some of the nerves that control the tear ducts pass through the middle ear, so occasionally infection in this area of the ear can damage the nerves.
Some of the sulfonamide class of drugs can cause damage to tear glands. Sulfonamides are used for treating bacterial infections.
Congenital (present at birth) problems with tear glands, such as malformed or absent are uncommon. They usually occur in small breeds.
Surgical removal of the third eye lid and tear gland due to cherry eye used to be a cause of dry eye. This is now infrequent, since surgical techniques have improved.
In many cases the cause of dry eye cannot be determined. The tear glands just stop working or shrink.
A number of breeds are predisposed to dry eye; they include Cocker Spaniels, West Highland Terriers, Bulldogs, Pugs, Shih Tzu and Lhasa Apsos. Age of the start of dry eye problems depends on the cause.
The Schirmer Tear Test is used to measure the volume of tear production.
A strip of filter paper (standardized absorbent paper) is placed in the inner corner of the eye for one minute. The amount of wetting is determined by measuring how far the edge of the wet area is from the end placed in the eye. This measurement is used to determine if there is a normal amount of tear production.
Whatever the cause of the dry eye, treatment with antibiotics and artificial tears will be started immediately.
The antibiotics will help control any infections.
The artificial tears (drops or ointment) will keep the eye lubricated, so that there is no further damage to the eye. The artificial tears will also flush out bacteria and any dirt, etc., that get into the eye.
Artificial tears should be used – not a saline eye wash. The artificial tears contain a number of ingredients required for the health of the eye, plus saline will irritate the eye further.
If no effective treatment is found, or treatment is partially successful, a dog will have to have artificial tears for the rest of it’s life. Artificial tear ointment is usually used in this case, since it needs to be applied less frequently than drops.
If a dog has stringy mucous, a vet will usually initially prescribe a mucolytic agent to break up the mucous.
If the dry eye is thought to be caused by an autoimmune response, or the cause is unknown, then cyclosporine is tried. Cyclosporine is an immunosuppressive drug that stops the destruction of the tear glands by the dog’s immune system.
Cyclosporin does not have an immediate effect, so it will need to be used for a while, before its effectiveness is assessed.
If cyclosporine treatment is not successful, another immunosuppressant, tacrolimus, may be tried.
Cyclopsorin, if it is effective, will need to be continued for life. If cyclosporine is stopped, or doses are missed, the immune system will start to attack the tear glands again.
Steroids may also be prescribed to help reduce inflammation. However, if the cornea (surface of the eye) has become ulcerated, steroids should not be used.
If none of the treatments work and the eye continues to be dry, then surgery may be tried. The surgery involves transplanting a salivary gland to the corner of the eye. Saliva then replaces the tear fluid. This is not ideal and can have several problems, including too much fluid creating a watery eye, plus the saliva itself may cause some problems to the eye. Surgery is usually a last resort.
Keratitis is an inflammation of the cornea (outer layer of the eye – see eye diagram). It makes the cornea look cloudy.
There are several types of keratitis. They should all be treated immediately. Untreated keratitis will lead to partial or complete blindness.
In addition to the cornea looking cloudy, there is usually watery eyes, squinting, and avoidance of light. Often the third eyelid sticks out. Frequently, a dog will paw at their eye.
Keratitis can be due to infection (bacterial, fungal or viral), pigment deposition in the eye, dry eye or extra growth of blood vessels and tissue in the eye.
The treatment of keratitis depends on the cause.
Some types of keratitis are not curable. The aim is to treat the symptoms, and slow or stop the progression of the disease.
Bacterial and fungal infections are treated with antibiotics.
Steroid ointments (for the rest of the dog’s life) can be helpful in reducing inflammation and slowing the growth of blood vessels. Long term use of steroids can have negative consequences (including potential development of Cushing’s disease). Therefore, the lowest effective maintenance dose will be used.
Eye disease can be serious and most are very painful. Seek treatment quickly to limit any possible permanent damage.
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