Protruding nictitating membrane (third eyelid)

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A. van Praag


Left: healthy eye, with barely visible third eyelid. The brown color at the edge of the eyelid  is seen in most rabbits

Right: Protruding third eyelid in a stressed rabbit



The protruding nictitating membrane (third eyelid) may be unilateral or bilateral.

It may be accompanied by enophthalmia (sunken eye).


Bacterial infection

Conjunctivitis, accompanied by purulent, fibrotic, granular inflammation of the third eyelid

Osteomyelitis, infection of the bone of the cheek bone


Respiratory distress

Lower respiratory tract infection, e.g., pneumonia

Congestive heart failure, with presence of fluids in the peritoneal cavity and compression of the lungs

Thymoma, or benign tumor of the thymus gland, leading to compression of the lungs


Mechanical” causes

Prolapse of the Harderian gland or “Cherry eye”

Atrophy of the eyeball mass

Corneal occlusion/pseudopterygium, symblepharon

Presence of a foreign body


Physiologic causes

Pain, may be accompanied by prolapse. Including pain related to disorders of the digestive tract, e.g., ileus, diarrhea


Relaxation, before sleep



Neurological causes





Laceration after a fight between rabbits


Genetic cause

Microphtalmia, or abnormally small sized eyeball


Neoplasia, cancer

Tumor of the eyelid, or the eye

Squamous cell carcinoma of the third eyelid (more common in third eyelid lacking a brown-colored edge)

Cancer of the cheek bone, leading to osteolysis, necrosis