Patent US 4,637,700

The invention relates to an ophthalmologic method for determining the refraction of the eye with a high time resolution. For the measurement an object is imaged onto the retina. In the light reflected by the retina the sharpness of the image of said object is determined depending upon its distance from the eye. The measurement is carried out with unvisible infrared light of a small band width. Consequently, the vision is not disturbed and the influence of the chromatic aberration of the eye is reduced. The method is not used to find the distance of the object with the best image. In contrast, two distances having the same degree of non-sharpness are determined. This procedure provides a differential signal having a good S/N-ratio for determining the refraction of the eye. The method and the apparatus are adapted for the automatic objective determination of the refraction, specifically the adjustment of the human eye to different distances depending on the time when the visual distance is changed, i.e. the method and apparatus is not only useful for determining the static but also the dynamic functions.