There are a number of conditions that cause a watery or mucus-like discharge to overflow the eyelids and run down the sides of the face, staining the hair. Cats do not cry as people do, so this is not a factor to be considered as one of the causes. In all cats with a runny eye, the cause should be determined so that proper treatment can be given.
First, it is important to determine whether the eye is red or irritated. Irritating eye disorders are characterized by excessive tearing along with a red or painful eye. However, if the eye is not red, then a blockage in the tear drainage system is the problem.
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Keep in mind that excessive tearing or a sticky, puslike discharge from the eyes or nose is frequently associated with feline viral respiratory infections. This possibility should be investigated before the eye alone is treated.
In cats with this condition, the discharge is due to an overflow of tears caused by a blockage in the tear draining system. Inadequate tear drainage should be considered if the cat has a persistent eye discharge without redness.
A cat may be born with an inadequate tear drainage system. However, in most cases, nasolacrimal occlusion is the result of scarring from eyelid injuries acquired in cat fights. Other causes are chronic infection in the duct system and plugging of the ducts by thick secretions, dirt, or grass seeds.
To see if the drainage system is open, a veterinarian stains the pool of tears near the inner corner of the eye with fluorescein dye. If the dye does not appear at the nostril, the tear duct is blocked on that side. Nasolacrimal probes are inserted into the duct opening, and various flushing techniques are used to show the point of obstruction. The flushing often removes the blockage and opens the duct.
An overflow of tears, accompanied by unsightly staining of the hair below the eyes, occurs in some cats with short noses, large, prominent eyes, and flat faces. The problem is seen most often in Persians and Himalayans, and other breeds with shortened muzzles. These breeds are subject to chronic eye irritations and infections that produce tearing. Their facial structure usually causes a narrowing of the nasolacrimal duct and a shallow tear lake at the inner corner of the eye. All these factors may contribute to the problem.