The cup-disc ratio is an indirect measure of the amount of neural tissue present at the optic nerve head. A large cup-disc ratio in a large disc may be accompanied by a normal neuroretinal rim. The area of the neuroretinal rim is relatively constant in normal persons and should relate to visual function. In 39 eyes of patients with suspected glaucoma, normal subjects, and patients with early open-angle glaucoma, biometric findings, psychophysical functions, and optic nerve measurements were studied. The area of the neuroretinal rim was determined from stereophotographs and corrected for the magnification by the optical components of the eye. A statistically significant relation between this neuroretinal area and parameters of visual function was found. The cup-disc ratio correlated more weakly with visual function. Covariant analysis showed the neuroretinal area to be the only parameter capable in our sample of discriminating among the three clinical groups.