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Dry eyes, also known as keratoconjunctivitis sicca, is a common problem seen in dogs. It occurs when there is a deficiency in the water portion of the tear film (which accounts for 95% of tear volume). As a result, the oil and mucus left results in the characteristic yellowish-green discharge from the eyes.
Function of tears:
-lubricate eyes
-contain anti-bacterial proteins and salt to flush away irritants and infectious agents
-tears bring sugars and oxygen to nourish the eye and remove metabolic waste
Consequences of dry eyes:
-eyes get irritated and inflamed
-cornea turns brown as a result of scarring
– thick greenish-yellow discharge in eyes
-blindness
Causes of dry eyes:
- Previous infection of the eye can damage the tear glands. Eg Canine Distemper infection in dogs, Feline Herpesvirus in cats.
- Exposure to certain drugs such as trimethoprim-sulfa.
- Immune –mediated destruction of the tear producing glands in the eyes. This is the most common cause of dry eye. Usually affecting breeds like West Highland White terriers, American Cocker Spaniels and Shih Tzus.
Diagnosis of Dry Eyes:
A Schirmer Tear Test (STT) strip is placed onto the lower lid of the eye in contact with the cornea to irritate the eye. The strip is left for 60s and the tear produced as a result of irritation wets the paper. The length of the moistened area is measured.
- A reading of 15mm is considered normal.
- 11-15mm is considered mild dry eye.
- < 5mm is considered severe dry eye.
Treatment of Dry Eyes
Tacrolimus eye drops
-These are very effective in improving tear quantity and reducing pigmentation of the cornea. As commercial products are not available for use, it is usually compounded for the animal.
Artificial tear solutions
– These products help to lubricate the eye. They can be purchased from most drug stores and are useful in mild cases.
Topical anti-inflammatories
-They are beneficial in reducing the inflammation associated with KCS. These are usually combined with topical antibiotics in the same solution.
With early diagnosis, prognosis for dry eyes is good. However, in late stages where significant scarring of the cornea is present, blindness is irreversible.