An ophthalmic optical power measurement device can include a light source configured to direct an input beam of light into the eye of a patient. The ophthalmic optical power measurement device can also include an aperture configured to receive an output beam that consists of light from the input beam that scatters from a location on the retina of the eye and exits through the pupil of the eye. The ophthalmic optical power measurement device can also include a detector configured to receive the output beam after it has passed through the aperture. A processor can be configured to determine the size of a spot created by the output beam on the detector, and to determine the optical power of the eye based upon the size of the spot.