An auto-refractometer according to this invention comprises a light beam source for producing a measuring ray wherein beams from a pair of invisible infrared ray emission diodes are alternately flickered, and real images of the beams are converged on respective sides of ridges at the output side of a V-shape coincidence prism at positions close to the ray axis thereby reducing the horizontal distance between the beams. A measuring optical system includes a transmitting collimater which projects said measuring ray passing through a vertical slit to permit focusing of a slit image on the retina. A receiving collimator collects beams reflected from the cornea and the retina, and by a semi-transparent mirror, and directs them via a reflection mirror to an interference bar which interferes with the beam from the cornea. A split prism divides the beam received from the retina, and a pair of elements photo-electrically convert the divided beam into electrical outputs. An electrical circuit includes a movable mechanism integrally associated with a lens system to focusing the image reflected from the retina on said split prism. The circuit produces high-speed flickering of the infrared ray emission diodes and responds to differential outputs from the photo-electric elements to cause said movable mechanism to move by an amount corresponding to the refractory diopter of the eye.
Auto-refractometer