KCS (DRY EYE)

 “Dry Eye”

(More formally known as “Keratoconjunctivitis Sicca” or “KCS”)

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. Keratoconjunctivitis sicca, abbreviated "KCS," means there is an 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, one is left with oil and mucus; hence, the gooey (classically described as "ropey") yellow eye discharge characteristic of this condition.

WHY DO EYES BECOME THIS DRY?

There are many causes of dry eye. Here are some of them:

• Canine distemper infection attacks all body interfaces with the environment including the eyes. Dry eye is part of the constellation of symptoms that can occur with distemper infection. (For more information on Canine Distemper infection click here).
• In cats, herpes upper respiratory infection can lead to a chronic dry eye. (for more information on herpes conjunctivitis click here).
• There could be a congenital lack of tear producing gland tissue (as described in certain lines of Yorkshire terrier).
• Exposure to sulfa containing antibiotics (such as Trimethoprim sulfa combinations) can lead to dry eye (which can be either temporary or permanent and occurs unpredictably).
• Anesthesia will reduce tear function temporarily (thus eyes are lubricated with ointment by the attending nurse.)
• Removal of the third eyelid tear producing gland (instead of replacing the gland in its proper location) during surgery for Cherry Eye can lead to KCS as can too much damage to the gland prior to proper gland replacement.
• A knock on the head in the area of one of the tear producing glands can lead to KCS.
• The most common cause of KCS appears to be immune mediated destruction of the tear producing gland tissue. We do not know what causes this type of inflammatory reaction but certain breeds are predisposed: the American Cocker Spaniel, the Miniature Schnauzer, and the West Highland White Terrier.

HOW WE MAKE THE KCS DIAGNOSIS

When KCS is in advanced state the situation is pretty obvious but in earlier cases in may look like a simple case of conjunctivitis. In either case it is important to actually measure the tear production to determine how dry the eyes are. The test that accomplishes this is called the “Schirmer Tear Test.”

To perform the test, a strip of special paper is inserted just inside the lower eyelid in the outer corner of the eye for 60 seconds. The moisture of the eye will wet the paper. At the end of the 60 second period, the height of the moistened area is measured. A height of 15mm or more is normal. A height 11-14mm is a borderline result. A height of less than 10mm is dry. A height less than 5mm is severely dry.

HOW DO WE TREAT THIS CONDITION?

Not that long ago all we had to treat this condition was tear replacement formulas and mucus dissolving agents. These are still helpful but require an impractical frequency of administration. A breakthrough came with the discovery of cyclosporine topical therapy to control the immune mediated gland destruction.

Cyclosporine is an immunomodulating drug that had already been found helpful to organ transplant patients. 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 restored. The success of this treatment plus its convenient dosing interval (1 - 3 times daily) has made this medication the primary treatment for KCS.

Occasional patients simply do not show a good response to cyclosporine ointment but will respond when the concentration is increased. Higher concentration products can easily be formulated by compounding pharmacies or one of the alternative medications listed below can be used. Treatment is almost always required for the lifetime of the pet.

Tacrolimus is another medication able to locally suppress immunity. This product has recently gained popularity in human medication as a topical anti-inflammatory treatment that is cortisone-free. It does not come in a formulation appropriate for eyes but can be made into one by a compounding pharmacy. It is used in a manner similar to cyclosporine and is generally of similar cost.

Pilocarpine is a cholinergic drug, which means it works on the autonomic nervous system (the part that controls automatic functions such as glandular secretion). This medication can be given for a particular form of dry eye known as Neurogenic KCS. In these cases, neurogenic stimulation of the tear gland is absent, so the pilocarpine is given in an attempt to stimulate the gland. Although the drug comes as an eye drop, for KCS it is actually given orally at an increasing dose until side effects are seen (diarrhea, drooling, vomiting). If side effects are encountered the dose is reduced to that which the animal tolerates. It is continued indefinitely or until the neurogenic KCS subsides, usually at twice daily. Neurogenic KCS typically affects only one eye.

Topical steroids may be beneficial in decreasing the inflammation associated with KCS. Typically they are combined with topical antibiotics in the same solution or ointment, especially when administered to dogs.

SURGICAL SOLUTIONS?

There is a surgical solution to KCS though it is a delicate procedure in general only done by veterinary ophthalmologists. This is called the 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 long duct. This duct can be carefully dissected out and moved so as to deliver saliva over the eye. Saliva actually makes a reasonable substitute for tears though in time some mineral deposits will form on the eye surface and eye drops may be needed to control this. The dog’s eyes will water when he is fed and facial wetting may be objectionable.

The pigment on the surface of the cornea resulting from long standing KCS is like the lens of dark sunglasses and interferes with a dog’s vision especially in dark situations. If tear function is restored, vision may also be restored via a procedure called a Superficial Keratectomy where the pigmented surface of the cornea is sanded away. This is obviously not worth doing if the tear issue is still problematic as the pigment would in that case just return. As with the parotid duct transposition, a veterinary ophthalmologist is probably best suited to perform such a procedure.

To locate a veterinary ophthalmologist in your area, please visit:

www.acvo.com  

For additional information about dry eye, Merck Animal Health (manufacturer of Optimmune^®) has put together www.dog-dry-eye.com where you can find videos, FAQ's and other material.

 Page last updated: 5/25/2023