To understand KCS, or dry eye, it
is beneficial to know how tears, or lack of them, effects the cornea.
The cornea is the optically clear
portion of the eye that allows entry of light into the eye. The healthy
cornea has no blood vessels, if it did it wouldn't be clear, so the nutrients
and oxygen that living tissue requires are supplied through a 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 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 mucous
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
and when advanced, drying of the entire corneal surface.
With the lack of the watery layer
of tears, the oil and mucus layers are increased. This leads to a
thick, mucoid, greenish discharge that sticks to the hairs around the eye.
It is imperative when the pet is displaying
signs of discomfort (rubbing face in grass, on rug, with paws) to get to
the veterinarian as soon as possible for a complete evaluation of the problem.
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