Meridional refractometry is a process whereby the meridional power of the corrective lens is measured in three predetermined meridians of the eye and the final prescription calculated from these data. The calculation is based on equations derived from Laurance's approximation of the meridional power of a cylindrical lens. The derivation of these equations, beginning with Laurance's approximation, is given. Prior knowledge of the position of the principal axes is not required, but the method is only applicable to the correction of regular ametropias.
Brubaker RF, Reinecke RD, Copeland JC. Meridional RefractometryI. Derivation of Equations. Arch Ophthalmol. 1969;81(6):849-852. doi:10.1001/archopht.1969.00990010851018