# Optical Behavior of an Enhanced Monofocal Intraocular Lens Compared with a Standard One
## 4 Discussion
Therefore, we can assume that compared with the enhanced EMV lens, the monofocal one presents a much flatter profile close to the optical center of the lens. The abrupt discontinuity in all the enhanced lens profiles in the peripheral zone, which was approximately +/ - 2.00 to 2.25 mm from the center (at the edge of the optical zone between 4 and 4.5 mm), could have been caused by the blending between the optic and the peripheral zones and is of little clinical relevance [25]. Despite this reduced power observed in the central zone, we believe this would not affect patient vision in the case of such a small pupil due to the stenopecic or pinhole effect that produces an increased depth of field, thus offsetting any retinal image blur caused by that possible refraction defect. The increased peripheral power of the enhanced model would produce the effect of an addition directly related to pupil size and the lens' nominal power, giving rise to more added power the greater the nominal power. Accordingly, the EMV monofocal lens is able to enhance intermediate vision by offering an overplus correction of 0.5 D to 1.00 D for pupil sizes of 2 mm and 0.8 D to 1.5 D for 4 mm pupils according to the lens' nominal power. These results align with recent publications by [PERSON] et al. [26] and [PERSON] et al. [27], who, in their optical bench studies, reported strong correlations between the performance of the RayOne-EMV lens, increased pupillary size, improved intermediate simulated VA, and reduced distance simulated VA and MTF. Spherical aberration is, by definition, a variation in the effective power of an optical system from the center to the periphery that remains constant across any lens meridian. Thus, this wavefront presents radial symmetry, with no dependence on the angular direction. For this reason, it is defined by central polynomials of the Zernike pyramid, which has 0 azimuthal orders, and therefore, these polynomials do not show dependence on the angular or azimuthal direction. It is common to identify spherical aberration with the so-called primary spherical aberration, as represented by the Zernike polynomial \(Z_{4}^{0}\). However, this is not the only polynomial that contributes to the spherical aberration of an optical system, as all central azimuthal orders above the fourth can do so, which is referred to as secondary spherical aberration. It is because of this that in this study, we considered all central polynomials of the Zernike pyramid so that we could better characterize the spherical aberration induced by the EMV lens examined. We detected significant contributions of the polynomials \(Z_{4}^{0}\), \(Z_{6}^{0}\) and \(Z_{8}^{0}\), although the SA of the eighth order had less influence and null contributions of \(Z_{10}^{0}\) and \(Z_{12}^{0}\) were found. As may be seen in Figure 3, the standard monofocal lens showed almost no aberration across the whole optic zone for the three nominal powers examined. However, for all three powers considered, the enhanced monofocal designs showed a similar aberration pattern such that their central 2 mm featured neutral spherical aberration and this gradually increased to 4 mm, reaching a value of around 0.05 microns, but with a significant drop for an optic size above 4 mm, where the SA changed to negative values (see Figures 3 and 4). This variation in spherical aberration from the central 2 mm toward the periphery (up to 4 mm) is consistent with the increase in positive power observed in the radial power map. Our analysis of RMS HOAs for the two IOL models revealed a stepwise behavior of the standard monofocal whereby, for both 3 mm and 4.5 mm pupils, the higher the lens power, the greater the HOA. The behavior of the enhanced monofocal was, however, flatter in that less variation was produced in aberrations measured for the three lens powers and for both pupil sizes. The increment in the HOA at the enhanced IOL periphery was a result of its aspherical design. However, in photopic conditions, this increment has no effect on patient vision for normal pupil diameters.