An apparatus for determining a position of a subjects cornea, comprisinga camera, a first illumination apparatus adapted to provide a first beam of lightand a first diffuse portion of light that are coincident, and a second illuminationapparatus adapted to provide a second beam of light and a second diffuse portionof light, that are coincident. In some embodiments, the first, second, thirdand fourth images are disposed on the midpoints of a square, when a cornea is locatedalong an optical axis of camera.
