Our results, mainly contained in
Table 3 and
Figure 2, are consistent with other results obtained by numerical simulation in related works.
2,7,8 They analyzed numerically the design of hybrid diffractive–refractive IOLs inserted in a polychromatic pseudophakic model eye. For instance, an aspheric monofocal hybrid IOL, proposed by López-Gil and Montés-Micó,
7 has the diffractive surface intended to correct for the eye's LCA. In this lens, the diffractive profile directs nearly all the incoming light to its first diffraction order, where diffractive and refractive powers add up and, as a result, a single achromatic focal point is formed for distance object imaging in a modified Navarro et al. model eye.
20,24 Castignoles et al.
8 paid more attention to the diffractive element of multifocal IOLs, more specifically, to the influence of the phase profile function (binary, parabolic, sinusoidal) on the distribution of EE between the ± 2, ± 1, and 0 diffraction orders. They extended their simulation beyond the design wavelength (λ = 550 nm) to include the effects of chromatism in a simplified eye model consisting of a planar diffractive element against a perfect lens equivalent to the human eye. A step closer to our study can be found in the comprehensive work done by Ravikumar et al.,
2 who further included three different hybrid IOLs: monofocal, nonapodized bifocal, and apodized bifocal, in their polychromatic analysis of IOL performance. In their numerical simulations, the authors used a reduced eye model optimally focused for distance objects at the wavelength
λ = 550 nm. The total refractive power of the reduced eye, coming from the combination of the cornea and the refractive portion of the hybrid IOL, was treated as corresponding to a single diopter at the cornea plane. An equivalent diffractive optical element at the corneal plane was computed to produce the same diffraction pattern on the retina as the physical diffractive profile virtually inserted in the IOL plane. Although the work reported by Ravikumar et al.
2 has provided a valuable basis for ours, some of their simplifications could not be assumed in our study. In particular, they assumed that the LCA of the Indiana eye chromatic model was a reasonable estimate for the LCA in pseudophakic eyes, thus neglecting the distinct contribution of different IOL materials (with different refraction index and dispersive characteristics) to the LCA of both the distance and near foci of the pseudophakic eye. As a consequence, they found in their simulations a uniform [LCA
D]
Eye ≈ 1.3 D in eyes implanted with either Tecnis or AcrySof lenses. In contrast to their simulated results, the formula we derived and our experimental results (
Table 3 and
Fig. 2) prove the role that the refractive features of 1f-IOLs and diffractive 2f-IOL materials (i.e., refraction index and Abbe value) play in the LCA of their image focal planes. In this regard, we have shown that the [LCA
D]
Eye may be significantly larger in the case of IOLs made of highly dispersive material, reaching values close to 3 D in distance vision. Moreover, we have also shown the influence of the refractive features of diffractive 2f-IOL materials on the achromatizing effect at near vision.