Protrusion, prolapse or elevation of the third eyelid refers to the abnormal elevation of the smooth inner eyelid that is located between the cornea and the inside corner of the eyelids closest to the nose. The third eyelid (TE) is usually retracted beneath the eyelids and barely noticeable. The third eyelid is also sometimes called the membrana nictitans or nictitating membrane.

Numerous disorders affecting the eye, TE and soft tissues behind the eye can result in TE protrusion. Therefore, TE protrusion represents a nonspecific symptom of ophthalmic disease that warrants further diagnostic evaluation.

The causes of protrusion of the TE fall into several categories:

Decreased or loss of function of the nerve supply to the smooth muscles of the TE and those surrounding the eyeball, from certain neurologic or systemic diseases

Relaxation of the muscles around the eyeball that work to keep the TE in the retracted position, from the use of tranquilizers, from poor physical health, etc.

Weakening of the ligament of the gland of the third eyelid with secondary glandular enlargement and prolapse (also known as cherry eye)

Tumors, cysts or inflammatory diseases of the TE

Any source of ocular (eye) pain that stimulates retraction of the eye deeper into the orbit (bony cavity in the skull or eye socket)

Any cause of settling of the eye deeper into the bony socket, such as from dehydration, weight loss, or changes in the structures behind the eye

Abnormally small sized eye. Small eyes may occur as congenital birth defects or may arise from shrinkage of the eye following severe trauma or inflammation.

Presence of a mass, such as a tumor, cyst, infection or inflammation within the orbit, and pushing the eye and the TE forward

What to Watch For

Increased prominence and elevation of the smooth inner membrane located at the inside corner of the eyelids

Other signs are dependent upon the cause of the prolapse. They may include squinting, tearing, changes in pupil size, alterations in the size or position of the eyeball, discoloration of the third eyelid, and deformities of the third eyelid.

The condition may affect one or both third eyelids.

Diagnosis

Diagnostic tests may include one or more of the following:

Complete medical history and physical examination

Complete ophthalmic examination including testing of pupillary light reflexes, Schirmer tear test, fluorescein staining of the cornea, tonometry to measure the pressure within the eye, and examination of the interior of the eye under magnification. Your veterinarian may refer your cat to a veterinary ophthalmologist for further evaluation using specialized instrumentation.

The third eyelid itself may be examined with a forceps after application of a local anesthetic.

Neurologic examination to assess the presence of neurologic disease

Complete blood count (CBC) and serum biochemistry tests to evaluate the underlying cause and identify any related problems

Skull X-rays to determine the presence of a bony orbital or sinus problem

Ultrasound examination of the eye and soft tissues within the orbit behind the eye

Specialized imaging tests such as computed tomography (CT) scan and magnetic resonance imaging (MRI) of the eye, orbit and brain

Treatment

Successful treatment requires obtaining an accurate diagnosis as to the cause. No symptomatic therapy can be initiated until the precise cause of TE elevation is identified.

Home Care

Vision is not usually compromised unless the third eyelid covers more than half of the eye. The underlying cause of the prolapse may affect vision, however. Confine your pet to a safe area until the cause of the problem is determined.

Do not administer human over-the-counter medications, such as Visine® or other ophthalmic remedies intended to "reduce eye redness" or irritation, because these medications rarely help the problem and may make diagnosis of the cause more difficult.