Toric lens volume

Theory is derived for the calculation of the volume of tyre- and barrel-form toric lenses. The integral produced is evaluated using an approximate method of integration. Differences between the two volumes are considered insignificant in the context of spectacle lens manufacture. Methods of approximating the volumes of both tyre- and barrel-form toric lenses are examined. An approximate method, relying upon standard formulae pertaining to the volume of the sphere and cylinder, is sufficiently refined for most practical purposes and obviates the use of a sophisticated calculator or computer.