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Keratoconjunctivitis sicca (KCS) or Dry Eye

 

Description of KCS

Keratoconjunctivitis sicca (KCS) or "dry eye" describes the changes in the eye which result from lack of tear production. To understand "dry eye" it is helpful to know how tears help keep the cornea healthy. The cornea is the optically clear portion of the eye that allows entry of light into the eye. Like all living tissue, the cornea requires a supply of oxygen and energy to remain healthy. Oxygen and nutrients are supplied to most tissues by the blood that moves through the area in blood vessels. The healthy cornea has no blood vessels, if it did it wouldn't be clear, so the oxygen and nutrients are supplied through the three-layered 'tear film.'

The outer most layer of the tear film is an oily layer supplied by glands in the eyelids. This layer helps prevent evaporation of the next aqueous layer. The middle layer is the liquid aqueous layer produced by the main tear gland and a gland in the third eyelid. This is the layer that is decreased in dry eye. 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.

A breakdown in the tear film and a loss of the aqueous layer causes dry eye. This loss results in dryness to areas of the corneal surface or in more advanced cases, drying to the entire corneal surface. When the cornea is deprived of oxygen and nutrients through the tear film, it rapidly undergoes destructive changes. These changes result in brown pigmentation, scar tissue growth, ulcer development, and blood vessel growth across the cornea leading to partial vision loss.

The eyes of a patient with KCS sting constantly just as ours do on a very windy day. The stinging we feel is due to the wind drying our eyes quicker than tears can be provided. Therefore, the patient with dry eye is uncomfortable almost all the time. When a patient has "dry eye" where there is a lack of the watery layer of the tears, the oil and mucus layers are increased. This leads to a thick, mucoid, greenish discharge that sticks to the hairs around the eye. Often this is the main reason that a patient is presented to the veterinarian. The discharge will clear up whenever any medication is used but will return when the medication is stopped. When this occurs, the patient is often referred to a veterinary ophthalmologist for further examination and treatment.

Diagnosis of KCS

Diagnosis is made by collecting a history about the condition, an examination, and a number of testing procedures. These tests include the Schirmer tear test which measures the production of watery layer. Fluorescein stain is used to define possible breaks in the corneal surface and the rate of the tear breakup. In addition, Rose Bengal stain may be used to evaluate the health of the outer layer of the cornea called the epithelium.

Causes of KCS

A number of causes have been reported for dry eye. These include hypothyroidism, infections of the tear glands such as canine distemper virus and immune-mediated diseases that attack the tear glands. Another frequent cause of dry eye is a toxic effect produced by certain sulfa-containing drugs and certain anti-inflammatory drugs. Some of these drugs may be necessary for the treatment of other diseases. In some cases, changing or stopping the medication may result in improvement of the dry eye, while in others the toxic damage is done and the KCS is not reversible, and must be managed medically. In many cases the cause of dry eye remains unknown yet treatment can still be instituted. Loss of nerve impulses to the gland due to long-standing ear infections and other nerve disorders will cause a unilateral (one sided) dry eye often combined with a dry nose in some cases.

Treatment of KCS

There are several objectives in treating dry eye. These include:

  • Tear Replacement
  • Lubrication
  • Reduce bacterial overgrowth
  • Reduce inflammation
  • Stimulate natural tear production.

Since the aqueous tear fraction is absent or reduced, tear replacement is very important. Natural tear production is continuous, so it is very difficult to replicate this with drops. Most owners with a bit of co-ordination with family members can manage to apply artificial tears 4 to 6 times daily. Commerical tear replacement products such as Tears Naturale II, Hypotears, and Isopto-Tears are suitable.

Artificial tears alone do not lubricate as well as natural tears, so we recommend the addition of a lubricant in addition to the use of artificial tear solutions. Lacrilube, Tear Gel or Hylashield Nite are suitable.

The dry eye patient frequently has a buildup of mucus in the folds of the eyelids that is no longer being washed with liquid tears. This mucus is food for bacterial growth. These bacteria may not be disease-causing bacteria but need to be controlled. In most cases an antibiotic and acetylcysteine (an ingredient which will help break down the mucus) are added to the artificial tear solution to help keep the mucus discharge and the bacterial overgrowth under control.

Topical anti-inflammatory drugs are indicated when the flourescein dye test shows no ulceration. This medication reduces inflammation and long-term scarring effects. Corticosteroids (cortisone drugs) cannot be used when ulcers are present because they decrease healing speed and enhance the ulcer process.

Occasionally patients with a nerve loss are treated with pilocarpine given by mouth. This drug stimulates the lacrimal gland to produce tear but may have undesirable side effects.

The newest drug used for the treatment of dry eye is an immune-suppressing medicine called cyclosporine. This medication has provided relief of symptoms in some patients while other patients have had a marked increase in tear production. A 0.2% cyclosporine ointment called "Optimmune" is a licenced product for dogs and has proven effective in many dry eye cases, while some dogs require a stronger (but unlicenced) 1% or 2% formulation of cyclosporine.

Outcome

Most patients with dry eye will do well if medications are administered on a timely basis. In cases where medicines cannot be given regularly or do not work, surgical techniques must be considered. A parotid duct transposition (surgical movement of a duct from a saliva producing gland) is available. In general, with good owner treatment, no patient need lose eyesight due to the dry eye condition.