© 2002 American College of Veterinary Ophthalmologists Veterinary Ophthalmology (2002) 5, 3, 221–226 Blackwell Science, Ltd CASE REPORT BILATERAL NEUROEPITHELIAL CHORISTOMAS Bilateral neuroepithelial choristomas of the optic disc in a cynomolgus monkey (Macaca fascicularis): a case report Robert J. Munger,* V. Behrana Jensen,† Thomas W. Bouldin‡ and Robert L. Peiffer, Jr‡ *Animal Ophthalmology Clinic, PC, 4444 Trinity Mills Road, Suite 201, Dallas, TX 75287, USA, †Sierra Biomedical Division of Charles River, Reno, NV, USA, ‡University of North Carolina, Departments of Pathology and Ophthalmology, Chapel Hill, NC, USA Abstract A 6-year-old intact male cynomolgus monkey of Chinese origin was received at the Sierra Biomedical Facility. While physical examination revealed good body condition with no abnormalities, routine ophthalmic examination revealed bilateral proliferative optic neuropathy involving the dorsal aspect of the optic disc. No changes were noted in the appearance of the lesions over 8 months, and fluoroescein angiography revealed no abnormalities other than obstruction of the view of the retinal vessels by the lesions. Histopathologic studies revealed characteristics consistent with a diagnosis of bilateral neuroepithelial choristoma. Key Words: choristoma, cynomolgus monkey, optic disc Address communications to: Robert J. Munger Tel.: (972) 267–4100 Fax: (972) 267– 4200 e-mail: eyedvm@aol.com INTRODUCTION Ophthalmic examinations of exotic and laboratory animals can be challenging because of the variability of the ocular fundi between species, and because reports of normal variations and naturally occurring lesions are relatively rare. The use of primates in ophthalmic research and toxicologic studies has become more common because the eyes of these species are similar anatomically and physiologically to human eyes. Because primates are a limited and precious resource, most research and studies have first been conducted in other species in greater numbers to ensure that investigations in primates are justified. It is imperative that a veterinary ophthalmologist is able to discern the significance of any lesions noted in the eyes of animals under study, especially when the numbers are relatively low as in primate studies. This case report describes a naturally occurring bilateral lesion of the optic disc in a cynomolgus monkey that was noted during routine health examinations in a primate colony. CLINICAL FINDINGS Initial ophthalmic examinations by Sierra Biomedical personnel identified bilateral white proliferative lesions near the superior border of the optic disc. Examinations by a board certified ophthalmologist (RJM) confirmed the presence of the lesions, which remained unchanged over the following 6 months. Menace and pupillary light responses were normal, and no evidence of visual impairment was evident. Slit-lamp biomicroscopic examinations revealed no abnormalities in the anterior segment, lens, or anterior vitreous. Indirect ophthalmioscopic examination revealed bilateral, proliferative, white lesions with irregular fuzzy surfaces. The lesions were irregularly ovoid, 0.1– 0.2 disc diameters in diameter, and appeared to be elevated with extension into the vitreous from the superior aspect of the optic disc. They obscured under- lying retinal vessels. The optic discs appeared otherwise normal, and no abnormalities of the vitreous or retina were evident. The lesions resembled proliferative optic neuropathy that has been described in horses, but they were bilateral and no progression or resolution was noted at any of the sub- sequent indirect ophthalmoscopic examinations. Figures 1a and b reveal the appearance of the lesions OU by fundus photography. Fluorescein angiography was performed 6 months after initial examinations and revealed no abnormalities with the exception that the lesions obscured the visualization of the underlying retinal vessels as was expected from indirect ophthalmoscopic examinations (Figs 2 and 3).