Toric periphery rigid lenses

Abstract

Lenses with toric peripheries and spherical optic zones have been advocated to improve the fit of rigid lenses on corneas with moderate astigmatism. However there is usually little discussion of the theoretical background to this fitting technique. A review of the manufacturing process permits the development of a model which will allow the computation of those optic zone data that are dependent on other specified lens parameters. These data then enable tear layer profiling to predict improvements in fit for specific lens designs and corneal models. Results from such calculations indicate that many lenses cannot be manufactured precisely as ordered and this could result in variability in specification and performance. The physical fit of tonic periphery lenses can be shown to be optimal when the selected parameters produce a monocurve back surface along the steep meridian. This is confirmed when fitting lenses in a clinical environment.