To achieve the clinical outcomes claimed for these monofocal enhanced IOLs, manufacturers need to deviate from the perfect monofocal optics to obtain a design that can generate a point spread function slightly more resilient do defocus than a typical monofocal design would. This is the case of both IOLs under analysis. It seems that both IOLs employ similar approaches to obtain functional intermediate vision that consists of aspheric surfaces with paraxial focal power above the nominal power that decreases very rapidly away from the center of the optical zone up to about 0.9 mm. After this point, the designs start to diverge from each other, with the Isopure showing a larger negative gradient in power that will overcompensate the average corneal spherical aberration [1]. This feature of the Isopure design is probably intended to further increase the DoFi for eyes with larger pupils. The increased negative spherical aberration in the Isopure design can be partially compensated by targeting a small myopic residual error, leading to a proportional increase of the lens central power, which will be equivalent to shift the power profile plotted in Fig. 1 up in the y-axis. On the other hand, if emmetropia is achieved for photopic pupil diameters, a likely consequence of this increased negative spherical aberration is that as the pupil gets larger, under low illumination levels, the Isopure design might induce a small hyperopic residual error. This effect was also measured by Azor et al. in an ISO2 optical bench setup, with an artificial cornea with a spherical aberration of + 0.27 µm for a 6-mm diameter [12]. These authors reported a hyperopic shift of + 0.20D and 0D for the Isopure and Eyhance, respectively, for an aperture diameter of 4.5 mm in the IOL plane, which corresponds to the diameter of the optical zone plotted in Fig. 1. The opposite effect, i.e., small myopic shifts, might also be expected with both lenses when the diameter of the optical zone being illuminated is around 2 mm, as reported by the same authors [12], which would be the case in an eye with an entrance pupil of about 2.4 mm. The agreement between the results reported by Azor et al. and the inferences made from the power profiles can be justified from the fact that the balance of energy at the image plane will be related to the ratio between the different refractive powers inside the area of the optical zone being illuminated [13]. For both IOL models under analysis, when the diameter of the aperture at the IOL plane is smaller than 2 mm (radius < 1 mm), light will be refracted only by the central part of the optical zone that contributes very little to distance; thus, a myopic shift occurs. This effect can either be positive or negative, depending at which distance the patient is looking at. In other words, one can infer the pupil dependence of these designs from looking at the power profile. This pupil-dependent behavior might impact the general satisfaction of patients, as their natural pupils change size under different illumination conditions. These aspects should be evaluated in future studies, through clinical quality of vision questionnaires and/or psychophysic testing.

The ex vivo fourth-order spherical aberration found agrees with the values reported by Alarcon et al. [4] for the Eyhance and the Tecnis standard monofocal (approximately − 0.22 and − 0.21 microns for a 4.5-mm optical zone, respectively), measured with the Hartman-Shack aberrometer Crystalwave (Lumetrics, Rochester, USA). The ex vivo fourth-order spherical aberration found for the Isopure is in close agreement with the value reported in Fig. 9C of its patent application [14], measured in an optical bench with a neutral spherical aberration cornea. The in vivo spherical aberration values also agree with previous results [15] that reported a more negative spherical aberration with the Isopure than with the Tecnis standard monofocal.

To our knowledge, this is the first study to conduct an objective evaluation and comparison of both the Eyhance and the Isopure IOLs. The optical characterization of both lenses in terms of its power profile can be found in the correspondent patent and patent application. The results obtained with the NIMO TR1504 seem to agree with the manufacturer’s description for the Eyhance, plotted in the patent’s Fig. 4 [16]. In the case of the Isopure, and although the patent application does not provide numerical data in the power profile of its Fig. 10A [14], the resemblance between its shape and the power profile measured with the NIMO is obvious.

The similarity obtained in the subjective results are also consistent with the similar refractive profiles measured with the NIMO TR1504, considering the average natural entrance pupil diameter of the patients (3.6 mm). Although the number of patients in the present analysis is low, the subjective through-focus performance of both the Eyhance and the Isopure is consistent with previous reports for monocular visual acuity defocus curves. For instance, Bova and Vita [15] reported mean monocular visual acuities in 42 eyes implanted with the Isopure of 0.18 and 0.28 LogMAR, at defocus positions − 1.00D and − 1.50D, respectively, which are in close agreement with the present findings (0.15 and 0.26 LogMAR, respectively). Stodulka and Slovak [17], who evaluated 36 eyes implanted with the Isopure, also reported similar mean monocular values of 0.18 and 0.30 LogMAR for the same defocus positions of − 1.00D and − 1.50D, respectively. For the Eyhance, the present results also agree with previous findings. Yangezes et al. [18] evaluated 71 eyes implanted with the Tecnis Eyhance. These authors reported mean monocular visual acuities of 0.10 and 0.20 LogMAR at − 1.00D and − 1.50D, respectively, which agree with the present findings.

In conclusion, both IOL designs use a similar approach to enhance the depth-of-field and provide functional intermediate vision. In the present findings, the Eyhance showed marginally better subjective performance than the Isopure at the target vergences between − 1.00D and − 2.00D. Although a small difference of 3 letters might approach clinical relevance, these results did not reach statistical significance and were not replicated by the objective findings.