Protruding nictitating membrane (third eyelid)

Differential diagnosis

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 (sucken eye).

Bacterial infection

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

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
	Dehydration
	Relaxation, before sleep
	Exhaustion

Neurological causes	Rabies
	Tetanus

Trauma

Laceration after a fight between rabbits

Genetic cause

Microphtalmia, or abnormally small sized eyeball

Neoplasia	Tumor of the eyelid, or the eye
	Squamous cell carcinoma of the third eyelid (more common in third eyelid lacking a brown-colored edge)

Drugs

Sedatives

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