The normal cup disc ratio is ?

Ans. is 'a' i.e., 0.3 The ratio of cup diameter to disc diameter is normally 0.3:1. Optic nerve head changes associated with glaucoma are thought to be seen prior to the development of visual field loss. The following changes are commonly seen in the optic nerve head in glaucoma : - Asymmetry of the cup: disc ratio (>0.2) between the two eyes - A localized notch or thinning of the neuroretinal rim - An enlarged cup: disc ratio (>0.5), especially if in the veical axis - Pallor of the neuroretinal rim - Superficial disc haemorrhages - Vascular signs suggestive of an acquired cupping, such as baring of the circumlinear vessels and 'overpass' of central vessels and - Parapapillary atrophy