Assessing the optical performance of multifocal (diffractive) intraocular lenses

Abstract

Background and purpose: While the optical performance of monofocal refractive lenses can be measured quite easily, more efforts are required to assess the performance of multifocal lenses, due to imaging to several foci. The purpose of this study was to develop a rugged test setup for evaluation of the optical properties of intraocular lenses (IOLs) in conformity to the International Standard ISO 11979.

Methods: We built a test setup in order to measure the point spread function and to determine the modulation transfer function (MTF) of IOLs. We measured three multifocal IOLs with (1) a diffraction limited model cornea and (2) an individualized aspheric model cornea which shows a significant amount of spherical aberration.

Results: All the three IOL samples tested showed a different impact of spherical aberration on the MTF. The bispheric lenses (Alcon and Dr Schmidt) showed a degradation of the MTF and Strehl ratio with model (2) compared to model (1). In contrast, the MTF of the Tecnis lens, which has a prolate aspheric front surface, improved dramatically in combination with model (2).

Conclusion: We demonstrated the functional capability of our measurement system by presentation of a set of working examples. Two different model corneas were used to study the influence of spherical aberration on the MTF of our working examples. An aspheric model cornea, which had already been shown to be suitable for testing monofocal aspherics, was shown to be well suited for testing aspheric multifocal lenses.