A prosthesis capable of being worn on the eye of a wearer having a convex surface and a concave surface. The prosthesis has an aperture widening zone for widening the natural palpebral fissure of the wearers eye. The aperture widening zone may include a surface feature having an outer slope, an inner slope, and a maximum added thickness delta located between the outer slope and the inner slope. At least a portion of the surface feature may be designed in using one or more spline curve functions. Methods for designing and manufacturing prostheses having a surface feature at least partially designed using one or more spline curve functions are also provided.
