Detection and resolution acuity was measured at 30 degrees in the periphery for sinusoidal gratings under differing amounts of optical defocus. Within the range–2.0 to +2.5 diopters defocus, detection acuity was higher than resolution acuity. As defocus increased, detection acuity decreased continuously but resolution acuity was little affected until around 2.0 diopters defocus. The results indicate that resolution performance is sampling limited in peripheral vision, even for significant refractive error, and is more robust than detection acuity to the effects of optical defocus.