Central vision in patients with retinal disorders has been studied with sinusoidal grating patterns. Impaired detection of fine high-contrast gratings has been observed in patients with retinitis pigmentosa and glaucoma despite 20/20 vision. Abnormal contrast sensitivity to coarse gratings occurred in patients with certain macular disorders and occasional glaucoma patients, some with near-normal Snellen acuity. Thus, contrast sensitivity measurements demonstrate central visual deficits not apparent with Snellen testing.