We measured resolution acuity at 12 different retinal locations using sinusoidal gratings in a group of normals, ocular hypertensives and glaucoma patients. Resolution was measured using both stationary gratings, which selectively stimulate parvocellular ganglion cells (P cells), and gratings which phase reversed at 30 Hz, which selectively stimulate a higher proportion of magnocellular ganglion cells (M cells). With stationary gratings, peripheral resolution was found to be significantly reduced in glaucoma patients and, to a lesser extent, in ocular hypertensives. When the stimuli phase reversed at 30 Hz these differences between groups were larger. The ratio of resolution with and without phase reversal also showed a significant difference between the three groups. These results provide strong psychophysical evidence for a selective loss of M ganglion cell density over P ganglion cell density in glaucoma.