Measurements of optic disc rim area are used to quantitatively evaluate the optic nerve head in open angle glaucoma. It has been suggested that disc rim area (neuroretinal rim area) is independent of disc size, unlike measurements of cup-disc ratio that co-vary with measurements of disc size. To test the relationships between topographic optic disc measurements and disc size, we used computerized image analysis (Rodenstock analyzer) of the optic nerve head to measure total disc area, cup area, disc rim area, and disc cup volume in 38 normal subjects. Magnification-corrected measurements of cup area, disc rim area, and cup volume were positively correlated with measurements of disc area. Measurements of disc rim area were therefore not independent of disc size in this group of normal subjects. A normal range of values for disc rim area can be predicted for an eye depending on the area of its optic disc. Sensitive predictions require further refinement based on the patient's age, race, and sex.