The aspherizing of intra-ocular lenses

While a spherically surfaced intra-ocular lens cannot be designed to give zero spherical aberration for the whole eye, aspherizing one surface of an intra-ocular lens can produce zero Seidel spherical aberration in a pseudophakic eye or set it to any desired level provided the corneal asphericity is known and this does not change with the operation. Equations for determining the asphericities are given. Asphericities for five lens shapes; the minimum spherical aberration lens and its reverse form, the equi-biconvex lens, the plano-convex lens and its reverse form are determined. The Seidel aberrations of eyes with aspherized intra-ocular lenses were compared with that of eyes with spherical intra-ocular lenses. While aspherizing eliminates the Seidel spherical aberration, some residual higher order spherical aberration exists and the amount of this residual spherical aberration depends upon the lens shape. However, this residual aberration can be reduced but not made zero by modifying the asphericity. For currently used plano-convex lenses, only the curves surface can be aspherized. The effect of variations in the anterior corneal asphericity on the necessary lens asphericity was also investigated.