We are reporting 2 cases of a congenital anomaly which is rare when occurring in an otherwise normal eye. Scheie and Adler1 (1941) reviewed the literature on the subject, finding 5 cases of partial aplasia of the optic nerve reported up to that time, and added 1 of their own. Another paper on this subject has since been published in Brazil.2
A brief review of the embryology of the optic nerve will facilitate understanding of the possible causes of the anomaly.3 The optic vesicle becomes the optic cup, beginning at the 4.5 mm. stage of development. This is brought about by the invagination of the outer wall, the future retina, to approximate the inner wall, the future pigment epithelium. Coincidentally, the fetal fissure forms along the ventrolateral surface of the optic cup and stalk. Mesodermal tissue then invades the optic cup through the fetal fissure, filling the