PURPOSE: To attain exact and objective measurement by irradiating an eyeball with the coherent light of a single wavelength component, changing a wavelength in a prescribed range while optical path difference to be based on the pupil axis length of two light waves, which are reflected with the cornea and eyeground, is measured as the phase difference of the two light waves and measuring the pupil axis length of a checked eye from the change quantity of this phase difference.
CONSTITUTION: Collimated laser light to be incident to an eye to be checked 8 is reflected on the surface of the cornea. Then, when such reflected light 9 and reflected light 10 form the retina are condensed by a lens 11, since the contrast of a concentric circle-shaped interference stripe, which is obtained by the interference of the two reflected light beams, goes to be the most satisfactory in a position where the beam diameters of the both reflected light beams go to be almost same, a pin hole or a ring slit 12 is arranged in such a position and the interference stripe is formed. The change of light and darkness in the formed interference stripe is detected by a photo-detecting element 13. The photo-electric converted electric signal of the photodetecting element 13 reflects the change of light quantity in the prescribed spot of the interference stripe. Then, since the output signal change of the photodetecting element 13 is analyzed by a processing unit 14 while the wavelength of a semiconductor laser element 3 is changed, the length of the pupil axis length is measured.
AITSU YOSHINAGA
FUJITA AKIHIRO
