What Good Are Tears ?

Imagine the discomfort of dry, irritated eyes and the relief and soothing after putting eye drops in.

 Tears provide lubrication for the eyes.  They contain antibacterial proteins, salts, sugars, and oxygen to nourish the eye.  Tears flush away irritants and infectious agents that constantly get in the eyes.  Because the outer portion of the eye doesn’t have a blood supply, the tears must bring sugars and oxygen to the eye  and must remove metabolic waste from the eye.  Tears consist of oil secreted by the eyelid glands, mucus and mostly water.  Tears are secreted by two “lacrimal” glands ;   one just above the eye and the other in the third eyelid, also called the “nictating membrane”. 

Without tears, the eye becomes very irritated.  The conjunctival tissues around the eye gets red, the cornea itself over time will turn brown in an effort to protect the eye, and a gooey yellow discharge will become apparent.  Blindness can result.

Keratoconjunctivitis sicca is a fancy way of saying the eye is dry.  “Kerato” refers to the cornea or clear covering of the eye that faces the outside world.  “Conjunctivae” are the moist pink membranes of the eye socket.  “Itis” means inflammation and “sicca” means dry.  KCS means inflamed dry cornea and conjunctiva.  It occurs when there is a deficiency in the water portion of the tear film which normally accounts for 95% of the tear volume.  Without the water, all that is left is oil and mucus ; thus the gooey yellow eye discharge of this condition.  

How Do Eyes Become This Dry ?

Below are a few of the many causes of dry eye:

• Distemper infection attacks all body parts that come in contact with the environment, including the eye.  Dry eye is part of the constellation of symptoms that can occur with distemper infection.

• Exposure to sulfa containing antibiotics can lead to dry eye, which can be either temporary or permanent and occurs unpredictably.

• Anesthesia will reduce tear function temporarily which is why eyes are lubricated with ointment following surgery sometimes.

• A knock on the head near the area of one of the tear producing glands can lead to KCS.

• Removal of the third eyelid tear producing gland during surgery for Cherry Eye can lead to KCS as can too much damage to the gland prior to proper gland replacement.

• The most common cause of KCS appears to be immune mediated destruction of the tear producing gland tissues.  No one knows what causes this type of inflammation reaction; however certain breeds seem to be predisposed : American Cocker Spaniel, Minature Schnauzer and the West Highland White Terrier.

How is KCS diagnosed ?

by a test called the “Schirmer Tear Test”.  The tear production is measured to determine how dry the eyes are.

How is KCS treated ?

 This condition used to be treated with tear replacement formulas and mucus dissolving agents.

 Now, KCS is treated with an immunomodulating drug called Cyclosporine which has been used for organ transplant patients.  Cyclosporine helps to control the immune mediated gland destruction.  When applied as an eye drop or ointment, it suppresses the immune destruction that is the most common cause of KCS and tear production is usually restored. 

Once started on cyclosporine treatment, it is necessary to have the eyes re-checked in about three weeks or so to check for any improvement.  This medication is normally given once or twice daily, however if there are no improvements, it can be increased to three times daily. 

Pilocarpine is what is referred to as a “cholinergic” drug which means that it works on the autonomic nervous system which is the part of the body that controls automatic functions such as gland secretions.  It can be given in the eye (topically) or given by mouth (orally) to stimulate tear production.  Used orally, it is given at an increasing dose until side effects are seen; such as diarrhea, drooling, vomiting or a drop in heart rate.  At that point, the dose is reduced and continued indefinitely, usually twice daily.  Pilocarpine does not increase tear production in normal dogs however. 

Artificial Tears can be obtained at any drugstore.  These can be combined with other therapies and can be very soothing.  The only problem with this is that they should be used 4 to 6 times daily.

Antibiotic products are often needed when treatment is first started for KCS because secondary infections are very common as the inadequate tears are not present to wash away infectious agents.  These products also do not increase tear production. 

Mucomyst eye drops are made from a respiratory product used to dissolve thick mucus.  Mucomyst helps remove the thick eye discharge that accompanies dry eye.  The active ingredient in Mucomyst is called Acetylcysteine. 

Severin’s solution is a combination of Mucomyst, Pilocarpine, artificial tears and antibiotic which can be made up.  This “recipe” originated by a veterinary ophthalmologist named Dr. Severin in 1996.  Many animal hospitals mix up their own concoctions based on this recipe.

Surgical solutions ?

There is a very delicate procedure called Parotid Duct Transposition which is normally only performed by a veterinary ophthalmoligist.  The parotid duct is the salivary gland on either sideof the facial cheek.  It produces saliva which is carried to the mouth via a long duct.  This duct can be carefully dissected out and moved to deliver saliva over the eye.  Saliva actually makes a reasonable substitute for tears, however over time, mineral deposits will form on the eye surface and eye drops may be needed to control this for the rest of the dog’s life.  The dog’s eyes will water when fed and some people may find this offensive.

The pigment on the surface of the cornea from long term KCS is like the lens of dark sunglasses and interferes with a dog’s vision, especially at night.  If tear function is restored, vision may  also be restored by a procedure called a Superficial Keratectomy where the pigmented surface of the cornea is sanded away.  It is not recommended if the tear tissue remains a problem as the pigment would just return.