An optical system for measuring retinal-image quality has a light system constructed and arranged to provide light to be directed onto a retina of a subjects eye, a detection system arranged to receive at least a portion of the light after being reflected or scattered back from the retina of the subjects eye, and an afocal optical system arranged in an optical path of the light between the light system and the detection system. The afocal optical system is constructed and arranged to correct a refractive error of the subjects eye.
