Unusual Coloboma of the Optic Nerve Entrance.

DEVELOPMENTAL anomalies of the eye in the region of the optic disc are commonly divided into two groups: those in which failure of coaptation occurs within the optic nerve sheath and those showing lesions of the peripapillary choroid or sclera. With the exception of the small holes sometimes seen on the anterior surface of the optic disc, which are probably related to aberrant formation of Bergmeister's papilla, the first type is much the less frequent of the two, and probably all the anomalies in the second group are formed by imperfect closure of the foetal fissure with the result that they appear on a line running inferiorly from the rim of the optic disc to the equator. The following report describes a coloboma of the optic nerve entrance of unusual configuration which does not belong to either group.