Liaison: Anngharaad “Annie” Reid
Keratoconjunctivitis Sicca (“KCS”) or Dry Eye is an eye disease. Keratoconjunctivitis sicca is a latin term. “Kerato” refers to the cornea or clear covering of the eye. “Conjunctivae” are the moist pink membranes of the eye socket. “Itis” means inflammation. “Sicca” means dry. KCS means inflamed, dry cornea and conjunctiva. Generally, it occurs when there is a deficiency in the water portion of the tear film which normally accounts for 95% of the tear volume.
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What is KCS or Dry Eye? It is an eye disease. Keratoconjunctivitis sicca is a latin term. “Kerato” refers to the cornea or clear covering of the eye. “Conjunctivae” are the moist pink membranes of the eye socket. “Itis” means inflammation. “Sicca” means dry. KCS means inflamed, dry cornea and conjunctiva. Generally, 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, the eye is left with oil and mucus; hence, the gooey yellow eye discharge characteristic of this condition.
Understanding Dry Eye/Why Tears are Good. Tears are important. They do more than just lubricate the eye. Tears flush away irritants and infectious agents and carry nutrients. Because the outer portion of the eye, or the cornea, does not have a blood supply, the antibacterial proteins, salts, sugars and even oxygen necessary to nourish the cornea are supplied through the three-layered “tear film.”
The outermost layer of the tear film is an oily layer supplied by glands in the eyelids. This layer helps prevent evaporation of the middle layer. The middle layer is the liquid aqueous layer produced by two lacrimal glands (one gland is above the eye and the other is in the third eyelid or “nictating membrane”). This is the layer that is decreased in “quantitative” KCS. The innermost layer in direct contact with the cornea is a mucous layer produced by glands located in the folds of the eyelid. The mucus layer helps the aqueous layer adhere to the surface of the cornea.
Without tears, eyes become dry and irritated and sting constantly. A dog with “dry eye” is uncomfortable almost all the time and much more prone to corneal ulcerations.
*A deficiency in the water portion of the tear film is referred to as “quantitative” KCS. A deficiency in the mucus and oil portion of the tear film is referred to as “qualitative” KCS. This discussion concerns “quantitative” KCS.
Signs and Symptoms
Dogs show their discomfort by rubbing their eyes, squinting and being sensitive to light. Their eyes may become red and inflamed and/or the cornea may appear dull and dry. There is commonly a thick, mucoid (or gooey) discharge in the eye or adhered to the eyelashes and hairs around the eye.
In time (if left untreated), the cornea will undergo destructive changes in an effort to protect the eye. These changes result in brown pigmentation, scar tissue growth, ulcer development and blood vessel growth across the eye. Blindness can result.
- By far, the most common cause appears to be an immune mediated destruction of the tear producing gland tissue. (The cause is unknown, but certain breeds, the Samoyed being one, are predisposed.)
- Chronic conjunctivitis (It is recommended that dogs exhibiting chronic recurring conjunctivitis be tested for adequate tear production to determine if they are suffering from early stages of chronic “dry eye.”)
- Infections of the tear glands (e.g., Canine Distemper)
- Loss of nerve impulses because of long-standing ear infections and other nerve disorders
- Exposure to sulfa containing antibiotics and the NSAID Etogesic (etodolac)
- Anesthesia (temporary). It is a good idea to ask your veterinarian to lubricate your Sammy’s eyes with ointment prior to surgery.
- Removal of the nictating membrane (instead of replacement) during surgery for Cherry Eye
Mode of Inheritance
The mode is unknown.
The “Schirmer Tear Test” (STT) is used to measure tear production. A measurement of 15mm or more is normal. A measurement of 11-14mm is borderline. A measurement of less than 10mm is dry. A measurement of less than 5mm is very dry. Fluorescein stain is used to define possible breaks in the corneal surface and the rate of the tear break up. Rose Bengal stain may be used to evaluate the health of the cornea’s epithelium.
Many dogs with STT measurements of less than 10mm may not show clinical signs of KCS.
Note: Treatment of animals should only be performed by a licensed veterinarian. Veterinarians should consult the current literature and current pharmacological formularies before initiating any treatment protocol.
There are several objectives in treating “dry eye.” These include:
- Tear replacement
- Reduce bacterial overgrowth
- Reduce inflammation
- Stimulate natural tear production
Because the aqueous layer of the tear film is deficient, tear replacement (artificial tears) is very important but requires an impractical frequency of administration. A breakthrough came with the discovery of cyclosporine topical therapy to control the immune mediated gland destruction (see below).
Artificial tears alone do not lubricate as well as natural tears, so the addition of a lubricant is recommended.
Reduce bacterial overgrowth
The “dry eye” patient frequently has a buildup of mucus in the folds of the eyelids that is no longer being washed away by tears. This mucus buildup is food for bacterial growth. An antibiotic and acetylcysteine are either added to or in combination therapy with the artificial tear solution to help keep the mucus discharge and bacterial overgrowth under control.
Topical anti-inflammatory drugs are indicated when the flourescein dye test shows no ulceration. Corticosteroids cannot used when ulcers are present because they delay healing.
Stimulate natural tear production:
Pilocarpine: Patients with nerve loss are treated with pilocarpine. Pilocarpine is a “cholinergic” drug – it stimulates the lacrimal glands to produce tears, but may have undesirable side effects (diarrhea, drooling, vomiting, drop in heart rate).
Cyclosporine: This is the primary treatment for “dry eye” because of its efficiency at stimulating tear production (dogs with Schirmer tear tests as low as 2mm still have an 80% chance of responding to cyclosporine), the need for fewer applications and the lack of undesirable side effects with long term use.
Cyclosporine is an immunomodulating drug that, when applied as an eye drop or ointment, suppresses the immune destruction that is the most common cause of “dry eye” and restores tear production.
Shering-Plough developed Optimmune® Ophthalmic Ointment, an eye ointment containing 0.2% cyclosporine.
Tacrolimus: Tacrolimus is one of a group of relatively new drugs called calcineuron inhibitors. These drugs are anti-inflammatory, and immunosuppressive or immunomodulatory. At the present time, tacrolimus is primarily used in the treatment of KCS and immune-mediated dermatologic diseases. Although cyclosporine has been the standard drug used to stimulate tear production, topical tacrolimus is thought to be considerably more effective and as a result may be useful for use in dogs that are unresponsive to cyclosporine.
Parotid Duct Transposition
The parotid duct is the salivary gland on either side of the facial cheek. It produces saliva which is carried to the mouth via a duct. This duct can be dissected and moved so to deliver saliva over the eye. Saliva is a reasonable substitute for tears although, in time, some mineral deposits will form on the eye surface and eye drops may be required to control this. The dog’s eyes will water when fed and facial wetting may be undesirable.
If the surface of the cornea becomes pigmented and interferes with a dog’s vision, the pigmented surface can sometimes be surgically removed. This procedure is rarely performed unless the primary underlying condition is well controlled to help prevent recurrence.