1. A method of determining an orientation of a Landold C in an image containing a plurality of pixels, the method comprising: determining a center of the Landolt C; extending a plurality of rays from the center of the Landolt C radially outward; determining a plurality of distances, where each distance of the plurality of distances represents a distance from the center of the Landolt C to a darkest pixel along each ray of the plurality of rays; identifying a peak in the plurality of distances; and determining the orientation of the Landolt C based on the peak in the plurality of distances.