A 60-year-old man had variable visual acuity especially in the right eye for 2 years. The right field of vision showed a hemianopic defect on the nasal side (in addition to reduced visual acuity which was due to nuclear cataract). A localized posterior cortical cataract on the temporal side of the right lens accounted for the nasal field defect since the defect disappeared almost completely on dilatation of the pupil, and completely after cataract extraction. Asymmetrical opacities in the optical media far enough anterior or posterior to the plane of the pupil will produce asymmetrical field defects. (An opacity close to the plane of the pupil will produce concentric constriction.)