A technique based on indirect ophthalmoscopy has been devised to enable measurement of structures in the posterior pole of the eye. It has been used to measure clinically the maximal and minimal diameters of both the optic disc and cup of 130 normal eyes from 66 patients and 33 optic discs from 20 patients with glaucomatous visual field loss. The disc area and neuroretinal rim area were derived mathematically for each eye. In the normal group the neuroretinal rim area was strongly correlated with the disc area (r = 0.89, P less than 0.0001). Only 9.1% of the glaucomatous group fell within the 95% prediction interval for the normal group, indicating a high degree of sensitivity and specificity for predicting the presence of visual field loss. Discs associated with mild field loss could be discriminated from those associated with moderate or severe field loss on the basis of disc and rim area measurements.