Coloboma of the optic nerve entrance.

THIS case of a coloboma of the optic nerve entrance is recorded because of the great scarcity of previous histological reports. Only very rarely is a coloboma found to be restricted to the optic nerve entrance (Duke-Elder, 1964); the great majority affect the adjacent choroid as well. Many of the early reports concerned eyes from animals or from anencephalic stillborn infants. These as well as the instances from otherwise normal humans were reviewed by Coats (1908). By 1943 about fifty cases had been reported, most of them without histological examination (Steinberg, 1943). The first histological report of a coloboma confined within the nerve sheath of a human eye that we have been able to trace is that of von Hippel (1898), who described a cystic excavation of the optic nerve. This apparently communicated with the vitreous by a narrow neck; both cyst and neck were lined by retina. Subsequent histological studies have been reported by Rochat (1913), Calhoun (1930), Wexler and Last (1938), and Pedler (1961). Cases with illustrations of ophthalmoscopic appearances but without histological reports are those of Nieden (1879), Szili (1887), Crampton (1913), Adler (1937), Steinberg (1943), Magnus (1946), Hughes (1947), Rio Cabaiias (1949), and Cashell (1951). There is probably no real difference between small colobomata of the optic nerve entrance and crater-like cavities or pits in the optic disc (reviewed by Greear, 1942).