Topography and longitudinal chromatic aberration characterizations of refractive–diffractive multifocal intraocular lenses

Purpose: Most optical systems present chromatic aberration quantified along the optical axis by the longitudinal chromatic aberration (LCA). LCA is controlled by the biomaterial Abbe number combined with diffractive effects, driven by the intraocular lens (IOL) topography. This study experimentally aimed at describing the effect in vitro of LCA in diffractive multifocal IOLs, with the help of dedicated optical benches and topographic characterization. Setting: Centre Spatial de Liège, Belgium. Design: Optical and topology analysis of various multifocal diffractive IOLs. Methods: Seven diffractive multifocal IOLs, available on the market and exhibiting different diffractive profiles, made from various biomaterials, were characterized under different wavelengths. Results: Through-focus modulation transfer function (MTF) curves and IOL diffraction efficiency depends on the incident light wavelength. In this study, the topology properties of various multifocal IOLs were investigated and their characteristics were correlated to their optical behavior for various wavelengths. Chromatic properties and their origins were then compared. As expected, diffractive and refractive effects were found to act in opposite ways, and could be partially or completely compensated. Conclusions: The LCA of each of the IOLs was evaluated in vitro. In most of the multifocal IOLs studied, some of the foci were found to be refractive, whereas others were diffractive. Although the results were not extrapolated to clinical relevance, it was shown, in some of the cases, that LCA could be fully compensated.