Systems and methods for modifying an eye including a light source with light elements, a photodetector producing a signal representing images of the light elements and corresponding to locations on an ocular surface, an optical system directing light from the light elements reflected by the ocular surface onto the photodetector, a memory including code for processing the signal, and a processor for executing the code and outputting shape data for use in calculating a treatment plan for the eye. The code includes instructions for determining the shape data based on a combination of zonal reconstruction and polynomial fitting using the plurality of images.