The Finished Single Vision are aspheric, the SFSV and D-28s are not; they are spherical in design. How do you know what the intermediate power is on a trifocal lens? Typically the intermediate power would be 50% of the prescribed add power. Other ... more

The front surface of an aspheric lens has curves that gradually flatten or steepen as they move away from the optical center of the lens. A non-aspheric or spherical lens has the same radius curve over the entire surface. Aspheric lenses will ... more