Digital Designs. In every basic optics course, ray tracing is taught to prove optical principles. Typical to most ray tracing diagrams are three or four rays of light to show the optical path of light through the system. Before digital computers were invented, ray tracing in detail was a laborious project. 

 

Today with computers and ray tracing software, it becomes possible to trace an infinite number of rays and analyze what happens optically to each light ray. This allows for the design of lenses that factor in spherical and other aberrations as the eye rotates to see through areas of a lens other than the optical centre. Today digital lens designs from all the major companies are very good and all are based on the same optical principles and digital ray tracing so the final lens designs are more similar than different.