Protrusion of the Third Eyelid
General information
Other common/scientific names: elevation of the third eyelid; protrusion or elevation of the nictitating membrane or nictitans; prolapsed gland of the third eyelid, nictitating membrane, or nictitans; haws syndrome; cherry eye
The third eyelid, also called the nictitans or nictitating membrane, is a conjunctival fold in the medial, or inner, corner of the cat’s eye. It lies between the cornea and the lower eyelid and consists of conjunctiva, a T-shaped piece of cartilage, some lymphoid tissue, and a gland which may be responsible for up to 40% of the tear production of the eye. The third eyelid is a moveable, protective structure of the eye which can be raised and lowered. It helps produce and distribute tears in the eye, and helps protect the cornea. In certain injuries to the cornea, the third eyelid will actually be therapeutically sutured to the upper eyelid to help protect the eye and facilitate healing. In a healthy eye, the third eyelid is not noticeable, or only barely noticeable, in the inner corner of the cat’s eye.
Causes
The third eyelid may protrude in only one eye, or may be present in both eyes. If only one eye is affected, the cause is likely related to that eye alone, while protrusion of both third eyelids is more likely a symptom of systemic disease.
Protrusion of the third eyelid is often seen with fever, dehydration, pain, vomiting and diarrhea, Horner’s syndrome, emaciation, muscle atrophy or paralysis of certain muscles of the head, prolapse of the third eyelid gland, gastrointestinal (GI) parasites, GI malfunction, a congenitally small eye, FeLV infection, painful ocular disorders, masses within the orbit of the eye, or masses of the third eyelid itself. Fatigue and tranquilization may also cause the third eyelid to protrude.
Cardinal symptom
Third eyelid elevated in the inner corner of eye
Symptoms
The third eyelid may be only slightly elevated from its normal position, or may be so greatly elevated that it obscures the cornea entirely, greatly impairing the cat’s vision.
This cat has protrusion of only its left third eyelid. The third eyelid of the right eye is in its normal position, and thus cannot be seen in the photograph.
Diagnosis
Diagnosis of protrusion of the third eyelid is made based on clinical exam. Since there are so many scenarios that can lead to protrusion of the third eyelid, determining the underlying cause will involve, at a minimum, a complete physical and ophthalmic examination. Further tests, such as bloodwork and imaging studies, may be needed to diagnose the underlying problem.
Treatment
The specific treatment will depend upon the underlying reason for the protrusion of the third eyelid gland. Medical therapies or surgery may be necessary.
Prognosis
The prognosis really depends on the underlying disease process, and can range from excellent (e.g., for a superficial corneal scratch) to grave (e.g., for aggressive, malignant masses within the orbit of the eye).