Editor, The three pillars of glaucoma diagnosis have been glaucomatous abnormalities of the optic nerve head, elevated intraocular pressure (IOP) and glaucomatous visual field defects. However, as perimetric defects have been reported to occur after the glaucomatous loss of optic nerve fibres has begun, it was the purpose of the present study to evaluate in a population-based investigation how many patients with glaucomatous optic nerve damage as defined by the appearance of the optic nerve head have a single normal IOP measurement. The results may provide information about the predictive value of IOP measurements in screening examinations for glaucoma, and may hint atthe proportions of subjects with normal-pressure glaucoma and highpressure glaucoma within the whole glaucoma group.