The simulation model allowed experimental calculation and comparison of retinal image quality of the different ablation profiles, based on the same patient collective.
Table 3 and
Figure 3D showed that the reduction of induced Z
4 0 using aspheric ablation profiles led to an improved retinal image quality (BCVSOTF) compared with the standard treatment (0
n). Although the differences were marginal at smaller pupil diameters, they were statistically significant at a 6-mm pupil diameter, where the greatest BCVSOTF difference (ΔBCVSOTF) could be found between the 0
n and the 3
n profile. This difference (0.22 log units) roughly equals two high-contrast logMAR steps and therefore can be considered clinically relevant.
19 Because of induction of negative Z
4 0 (overcorrection) and the relative high Z
6 0 induction, the 6
n profile contained steeper slopes and thus showed a behavior different from that of the 0
n, 1
n, and 3
n profiles. Compared with the 3
n profile, the 6
n profile decreased BCVSOTF more at smaller pupil diameters. This effect, which could also be explained by the Z
4 0 overcorrection and higher induction of Z
6 0, was reduced for diameters larger than 6 mm (
Fig. 3D). Because SA can enhance depth of focus
16,27 and there is evidence that the reduction of SA by aspheric intraocular lenses (IOLs) can compromise depth of focus,
28 it seemed necessary to investigate depth of focus of the different profiles. We calculated depth of focus by defocusing the LOA-optimized simulated postoperative WFE and used the metric VSOTF as the criterion of optical quality (optical depth of focus). The cutoff from the maximum VSOTF (in-focus) was set to −0.2 log VSOTF units. Depth of focus simulation showed that there were no differences between spherical and aspheric profiles for a 3-mm pupil diameter and only marginal differences for a 6-mm pupil diameter (
Table 5,
Fig. 6). This could be explained by the fact that the treatment left residual primary and secondary SA in postoperative eyes that still affected depth of focus. Like the curves of WFE and VSOTF as a function of pupil diameter, the defocus curves of the 6
n profile were of different shape with a sharp dip around −2.25 D (3-mm pupil diameter) and −1 D (6-mm pupil diameter), most likely due to induction of negative Z
4 0 and positive Z
6 0. Even though they were statistically significant, we believe the differences in depth of focus to be negligible because they were not noticeable for the near-vision–important 3-mm pupil diameter and they were small over a 6-mm diameter.