by Dawn R. Cole

Created on: February 26, 2010   Last Updated: February 27, 2010

A cat's third eyelid, also known as a haw or nictitating membrane, is a thin, pliable, triangular layer of conjunctival tissue located in the inside corners of each eye.   Normally, the haw is not visible unless the cat has suffered an injury or is ill, but there are some cats whose haw will show when they are sleepy, relaxed, or very content.   As long as the haw retracts, and remains retracted, when these cats are startled, there is no cause for alarm.   Pet parents should know what is normal for their own cat and get them to a veterinarian as soon as any ocular abnormalities appear.

Common Problems of the Third Eyelid

1. Injury = lacerations, chemical exposure, or trauma to the ocular region.   Outdoor cats run the risk of getting into fights with other animals, scratching their eye on branches, getting hit by a car, etc.   Cats who remain inside can sustain ocular injuries from sharp household objects, chemical splashes (like cleaning products), irritants, and other pets.  In both instances, injuries can also occur from mistreatment or abuse from humans.

2. Illness = the third eyelid can become visible, opaque, and protrude in response to a variety of illnesses:

a. Infections of the conjunctiva
b. Upper respiratory (viral or bacterial) and middle ear infections
c. Dehydration, chronic weight loss, fever, or anemia
d. Tetanus (protrusion of the nictitating membrane from muscle spasms around the eye)
e. An abscess from infected tissue behind the eyeball
f. Hematoma (bleeding behind the eye)
g. Tumors: squamous cell carcinoma, melanomas, and other neoplasms

3. Horner's Syndrome = can result as a consequence of injury, a middle ear infection, or some type of cancer involving the nerves in the neck or middle ear.   This syndrome can cause the cat's eye to become sunken, the third eyelid to prolapse (protrude), and the pupil to become abnormally small.

4. Cherry Eye = is a condition that occurs when the gland of the third eyelid becomes everted or prolapsed.   This gland is one of the most important tear-producing glands.  If it is displaced from its normal position, it will not function properly.   For unknown reasons, the cartilage of the haw folds over and, not only is it unsightly; it leads to excessive tearing, irritation, inflammation, and, can cause corneal lacerations.  The Burmese breeds are particularly susceptible.

5. Haw Syndrome = this is a common, but temporary protrusion of the haw that is usually seen in cats under the age of 2 and is usually accompanied by gastrointestinal problems.

Whether from an injury or an illness, conditions affecting the third eyelid are painful and will continue to worsen without medical treatment.  Prompt veterinary attention is required to prevent corneal damage and provide appropriate diagnosis and treatment for underlying infections or illnesses.  

For more information on problems with a cat's third eyelid:

www.medicinenet.com/pets/cat-health

http://pets.webmd.com/cats/cats-third-eyelid-problem s

www.sniksnak.com/cathealth

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