every .25D =
.05mm radius
converting Diopters to radius and vica versa
337.5/[diopter power/radius(mm)]
spherical equivalent
divide cyl power in half and add it to sphere power
f=Diopter power/(1-original lens power x distance (m) lens is moved
Vertex formula
moving lens toward eye
converting spectacle RX to CL Rx
make distance positive
moving lens away from eye
converting CL RX to spectacle RX
make distance negative