1. An apparatus for measuring a subject's eye having an instrument axis, comprising: a slit projector for projecting slits of light; at least one sensor, the apparatus adapted to form a first image of light from a first slit on the at least one sensor after the light scatters from the eye along a first pathway, and the apparatus adapted to form a second image of light from the first slit on the at least one sensor after the light scatters from the eye along a second pathway; a processor operatively coupled to receive the first image and the second image, the processor adapted to perform a projective transformation of the second image and to combine data from the first image and the second image, after it is transformed, to form a third image.