Abstract: An ophthalmologic apparatus includes an illumination system that is supported to be rotatable about a subject's eye with an irradiation direction of illumination light kept toward the subject's eye and an observation system that has a camera device and is arranged opposite to a position of the subject's eye across the illumination system. The camera device includes an imaging unit that receives reflection of the illumination light from the subject's eye and a light emitting unit for background illumination that is provided in the observation system and located below the subject's eye.

Abstract: A second harmonic generation (SHG) device is used for conversion of wavelength. The direction of polarization of light beams is suitably rotated by a direction-of-polarization rotating unit, for example by 45.degree., and thereafter these light beams are guided into the SHG device. This can minimize attenuation of intensity of light beam due to conversion of wavelength. Hence, using this direction-of-polarization rotating unit in the apparatus for measuring the medium, the intensity of light being incident upon the photodetector can be increased, whereby the refractive index of the medium can be measured more accurately than by the conventional apparatus.

Abstract: The present invention relates to an optical interference measuring apparatus and method for measuring displacement of an object. The apparatus and method reduces the displacement-measurement error caused by changes of the refractive index of the atmosphere or the like, in a measurement optical path and a reference optical path, by suppressing crosstalk caused by unfavorable mixing of reference light and measurement light with each other, thereby improving accuracy in the measurement. The apparatus produces interference between a measurement light beam and a reference light beam. The measurement light is propagated through a measurement optical path including a measurement reflector, which is at least movable along the measurement optical path. The reference light is propagated through a reference optical path including a reference reflector. The interference occurs in a predetermined interference system, whereby the displacement of the measurement reflector can be measured.