Spherical lens versus aspheric artificial cornea for intraocular lens testing

Recent versions of the International Organization for Standardization (ISO)-based model eye for intraocular lens testing include an artificial cornea whose spherical aberration is chosen to match the value of a human cornea. Aspheric lenses have been used as artificial corneas, but they are expensive and difficult to manufacture. This Letter demonstrates that the aspheric lens can be advantageously replaced with a simple biconvex spherical lens of the same focal length and similar wavefront error. A linear dependence is shown between the Coddington shape factor of the spherical lens and the value of the induced spherical aberration. This relationship is used to match the wavefront error of the spherical lens to the one produced by the aspheric lens. A modified ISO model eye, containing this alternative spherical lens as the artificial cornea, is proposed for the on-axis optical assessment of intraocular lenses. Its suitability for off-axis testing is discussed.