Colobomas of the optic nerve and of the macula are among the more interesting of ocular anomalies. The literature contains many clinical descriptions but relatively few anatomic studies of these defects. Caspar1 in 1887 classified colobomas of the nerve clinically on the basis of the arrangement of the blood vessels as they emerged from, and distributed themselves on, the disk. It was soon learned, however, that there was little correlation between the microscopic structure and the appearance of the fundus and that wide differences existed in the cases in which anatomic study was possible.
Most authors agree that colobomas are due to faulty development in the elements comprising the tissue "anlage." Often these tissues are modified or replaced by other tissues, and alterations may occur in tissues surrounding the coloboma as well. Coloboma of the nerve is due to anomalous closure of the fetal cleft and occurs in its