Abstract

Apparatus and method provide for automatically measuring the refractive error of a subject's eye and thus the prescription for lens or eye glasses for correcting this error. Under the control of a programmed automatic data processing system, an objective refraction measurement is made. Test symbols are then alternately presented to the subject under control of the data processing system. The symbols are viewed by the subject through an optical system whose refractive power may be continuously varied under control of the data processing system. The initial setting of the optical system is based upon the objective refraction measurement. The data processing system varies the size of the symbols presented to compensate for the power of the optical system so that a given symbol will appear to the subject to be of constant size. In one illustrative embodiment of the present invention, the subject communicates with the data processing equipment via a subject response device to indicate his preference for one or the other of the presented symbols. The data processing system interprets the responses to modify the setting of the optical system, alter the presentation of symbols and elicit another response from the subject. The subjective refraction is continuously monitored by objective refraction to ensure optimization of the refractive correction.