Presumed congenital nictitating membrane dysplasia in a Japanese white rabbit

Objective: The present report characterises a spontaneous nictitating membrane abnormality in a Japanese white rabbit. Animal studied: The animal was a male Japanese white rabbit (Oryctolagus cuniculus, Kbs:JW, 10 weeks old at the time of purchase) that had not received any treatment. A morphological abnormality of the nictitating membrane in the animal's right eye was detected. Procedures: Ophthalmological examinations, including slit-lamp biomicroscopy, corneal and conjunctival staining with fluorescein and lissamine green, fundoscopy, blinking rate measurement, Schirmer's tear test, and tonometry were performed. The animal was euthanised at 15 weeks of age, and histopathological examinations of the abnormal nictitating membrane, palpebral conjunctiva, eyelid and eyeball were performed. Results: The tip of the nictitating membrane adhered to the palpebral conjunctiva of the medial canthus. The eye and periocular tissues showed no abnormalities in the ophthalmological examinations, except for the structure of the nictitating membrane. Histopathological examination revealed that the adhered site of the nictitating membrane and the palpebral conjunctiva consisted of dense fibrous connective tissue that was consecutive to the conjunctiva adjacent to the eyelid margin and lamina propria of the nictitating membrane. The fibrous connective tissue was covered with stratified squamous epithelium. Conclusion: Based on these results, we diagnosed this abnormal finding as congenital nictitating membrane dysplasia. This paper is the first case report describing a congenital structural abnormality of the nictitating membrane in a Japanese white rabbit.