A system for shape determination for a surface of an eye, comprising: a light source (112, 122) comprising a plurality of light elements; a photodetector; an optical system for directing light from the light elements reflected by a surface of the eye onto the photodetector, the photodetector configured to produce a signal comprising a plurality of images of at least some of the plurality of light elements, each image corresponding to a location on the surface of the eye; a memory including programming code for processing the signal produced by the photodetector; and a processor for executing the programming code and outputting shape data for use in calculating a treatment plan for a corneal refractive procedure on the eye; wherein the programming code comprises instructions for determining the shape data based on a combination of zonal reconstruction and polynomial fitting using the plurality of images, wherein the zonal reconstruction comprises: determining a light pattern from the plurality of images, the light pattern representing the surface of the eye; forming a plurality of neighborhoods of vertices based on the light pattern; and fitting a polynomial to each neighborhood of the plurality of neighborhoods; characterised by the forming a plurality of neighborhoods comprises a Delaunay triangulation of the vertices wherein the zonal reconstruction further comprises filtering unwanted neighborhoods from the plurality of neighborhoods prior to fitting a polynomial by eliminating Delaunay triangles having at least one vertex angle below a predetermined minimum. a light source (112, 122) comprising a plurality of light elements; a photodetector; an optical system for directing light from the light elements reflected by a surface of the eye onto the photodetector, the photodetector configured to produce a signal comprising a plurality of images of at least some of the plurality of light elements, each image corresponding to a location on the surface of the eye; a memory including programming code for processing the signal produced by the photodetector; and a processor for executing the programming code and outputting shape data for use in calculating a treatment plan for a corneal refractive procedure on the eye; wherein the programming code comprises instructions for determining the shape data based on a combination of zonal reconstruction and polynomial fitting using the plurality of images, wherein the zonal reconstruction comprises: determining a light pattern from the plurality of images, the light pattern representing the surface of the eye; forming a plurality of neighborhoods of vertices based on the light pattern; and fitting a polynomial to each neighborhood of the plurality of neighborhoods; characterised by the forming a plurality of neighborhoods comprises a Delaunay triangulation of the vertices wherein the zonal reconstruction further comprises filtering unwanted neighborhoods from the plurality of neighborhoods prior to fitting a polynomial by eliminating Delaunay triangles having at least one vertex angle below a predetermined minimum. determining a light pattern from the plurality of images, the light pattern representing the surface of the eye; forming a plurality of neighborhoods of vertices based on the light pattern; and fitting a polynomial to each neighborhood of the plurality of neighborhoods; characterised by the forming a plurality of neighborhoods comprises a Delaunay triangulation of the vertices wherein the zonal reconstruction further comprises filtering unwanted neighborhoods from the plurality of neighborhoods prior to fitting a polynomial by eliminating Delaunay triangles having at least one vertex angle below a predetermined minimum.