Birefringent multifocal lenses: theory and application to the correction of refractive error.

Light passing through birefringent materials experiences two indices of refraction, and lenses made of or incorporating birefringent materials will therefore exhibit two focal points. The optics of birefringence are summarized, and their application to lenses is described. Prototype lenses based on these principles were produced, and the bifocal effect was observed. Multifocal lenses based on these principles have numerous uses, including contact and intraocular lenses.