Polychromatic Image Performance of Diffractive Bifocal Intraocular Lenses: Longitudinal Chromatic Aberration and Energy Efficiency

The study evaluated-theoretically and experimentally-the longitudinal chromatic aberration (LCA) and through-focus energy efficiency (TF-EE) of diffractive-refractive bifocal intraocular lenses (2f-IOLs). Four aspheric 2f-IOLs (Tecnis +4.00 diopter [D] ZMA00, +2.75 D ZKB00, and AcrySof +4.0 D SN6AD3, +2.5 D SV25T0) of same base power 30 D, but different design, additional (add) power, and different material, were tested in vitro in terms of TF-EE when illuminated by 3 red (λ(R) = 625 nm), green (λ(G) = 530 nm), and blue (λ(B) = 455 nm) lights. The LCA affecting the distance and near foci was derived theoretically and measured experimentally from the contributions of the IOLs' refractive and diffractive powers. Longitudinal chromatic aberration was evaluated in a pseudophakic schematic eye. The distance focus of all 2f-IOLs showed lower energy efficiency (EE) for the blue than for the red light. AcrySof IOLs showed the largest amount of positive LCA in the distance focus that, combined with corneal LCA, would increase the resulting distance LCA in a pseudophakic eye. The near focus of all 2f-IOLs showed higher EE for the blue than for the red light. Better compensation for the LCA of a pseudophakic eye at near focus is obtained with Tecnis than with AcrySof 2f-IOLs. The energy distribution between the foci of diffractive 2f-IOLs depends on the lens design, the illumination wavelength, and to a lesser extent, the add power. In distance vision, 2f-IOLs' refractive base power increases the positive LCA of prior ocular media, and the resulting LCA may even surpass the natural LCA of human eye. In near vision, however, the achromatizing effect of diffractive 2f-IOLs may compensate, in part, the natural eye's LCA.