shaped or wavy manner the three dimensional coordinates of the cornea surfaces and lens surfaces are then obtained together with the z coordinates of short coherence interferometry in order to implement topographic data acquisition in this manner it must be possible to control the measurement beam at selected locations on the two dimensional pupil as is described in fig3 this is possible by means of a pair of scanning mirrors 72 and 72 u2032 whose axes of rotation extend normal to one another in fig3 for example the axis of rotation of mirror 72 lies in the drawing plane and the axis of rotation of mirror 72 u2032 is oriented normal to the drawing plane finally it is noted that the scanning of the reference beam can also be carried out in another way other than by the moving mirror 21 for example by arrangements such as those described in application a 472 99 u201c periodically operating optical path length modulator u201d the scanning of the optical length of the reference arm can also be replaced by scanning the optical length of the measurement arm as is shown in fig4 in this case the measurement beam 4 is reflected to a roof prism 51 by a deflecting mirror 50 and is.