Convert plus cylinder prescriptions to minus cylinder prescriptions or vice-versa.
Calculate what magnitude and orientation of oblique Fresnel prism.
Calculate contact lens power from spectacle Rx.
Estimated residual astigmatism based off corneal Ks.
Calculate visual acuity from letter size and distance.
Calculate visual acuity from cy/cm and distance.
Calculate spectacle Rx from a contact lens Rx.
Calculate lens power given two vertex distances.