The optic disc i : Classification in glaucoma

The pale, cupped disc found in the final stages of glaucomatous disease has been known from the time of Von Graefe (I854). Since then many observers have described changes that occur at the optic disc in chronic, simple glaucoma. There has been particular interest in changes which may occur in the early stages of the disease. Studies of the normal population have shown that while there is a wide diversity in the appearance of the normal optic disc, in a single subject (Armaly, I969; Fishman, I970; Kolker and Hetherington, 1970; Portnoy, 1973) the two discs are remarkably similar (Witsiuk, I966; Kronfeld, 1970; Woodruff, 1970; Portnoy, I973). In contrast, individuals with glaucomatous disease usually show manifest asymmetry of the two optic discs (Fishman, I970; Kolker and Hetherington, 1970). Many criteria have been used to describe the glaucomatous optic disc. Important among these is the ratio of the cup diameter to the diameter of the entire disc (Pickard, I923; Snydacker, I964; Hollows and McGuiness, I967; Armaly, i967, I968; Schwartz, I973; Tomlinson and Phillips, I974). This was initially measured horizontally, but recently measurement of the vertical cup to disc (C/D) ratio has been stressed, after recognition that changes in the optic cup tend initially to affect the vertical diameter (Chandler and Grant, I965; Kronfeld, I967; Kirsch and Anderson, 1973; Weisman, Assif, Phelps, Podos, and Becker, 1973). Stereoscopic examination of the optic disc in early glaucoma reveals signs which help to distinguish the normal from the glaucomatous cup (Anderson, I975; Reed and Spaeth, I974). These signs are evidence for acquired tissue loss and account for the asymmetry previously noted. Tissue loss may appear in a variety of forms: thinning of the neuroretinal rim, either localized or generalized; depression or steepening of the walls of the cup (the tinted hollow (Reed and Spaeth, 1974) or saucer);