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The purpose of this work was to evaluate peripheral image quality in the pseudophakic eye using computational, physical, and psychophysical methods. We designed and constructed a physical model of the pseudophakic human eye with realistic dimensions using a corneal phantom and a board-only camera that was pivoted around an axis that matched the anatomical center of a human retina, assuming a radius of curvature of 12 mm, while it was submersed in a 23.4 mm long water filled chamber to emulate human ocular axial length. We used this optical setup to perform direct recording of the point spread function (PSF) and the associated retinal images for a commercial intraocular lens (IOL). Additionally, psychophysical tests were carried out to investigate the impact of the off-axis astigmatism in peripheral visual performance, where spectacle-induced astigmatism simulated the pseudophakic conditions in healthy subjects. Our findings using the physical eye model confirm the existence of large amounts of astigmatism in the periphery of the pseudophakic eye. The psychophysical tests revealed a significant reduction of detection sensitivity in the peripheral visual field. The latter suggests that off-axis astigmatism in patients implanted with IOLs may have performance and safety implications for activities requiring efficient peripheral vision.
To evaluate the impact of multifocal contact lens wear on the image quality metrics across the visual field in the context of eye growth and myopia control. Two-dimensional cross-correlation coefficients were estimated by comparing a reference image against the computed retinal images for every location. Retinal images were simulated based on the measured optical aberrations of the naked eye and a set of multifocal contact lenses (centre-near and centre-distance designs), and images were spatially filtered to match the resolution limit at each eccentricity. Value maps showing the reduction in the quality of the image through each optical condition were obtained by subtracting the optical image quality from the theoretical physiological limits. Results indicate that multifocal contact lenses degrade the image quality independently from their optical design, though this result depends on the type of analysis conducted. Analysis of the image quality across the visual field should not be oversimplified to a single number but split into regional and groups because it provides more insightful information and can avoid misinterpretation of the results. The decay of the image quality caused by the multifocal contacts alone, cannot explain the translation of peripheral defocus towards protection on myopia progression, and a different explanation needs to be found.
A closed feedback loop between the level of retinal blur and the subsequent growth of the eye is widely described in the literature (for review see Wallman and Winawer 2004)10. The leading hypothesis also assumes, that outside of the emmetropization process, eye growth is driven by the level of blur in the periphery10,11,12,13. The peripheral aberrations that comprise peripheral blur, are known to be dominated by astigmatism even when no astigmatism is present in the fovea14,15. This astigmatism together with comma and trefoil varies rapidly across angles while the rest of the high order aberrations remains mainly independent of the angle16,17. As a result of this angular dependence, asymmetrical aberrations increase with eccentricity and results in an oriented point spread function (PSF) with a decrease in the image quality. However, as a result of the reduced resolution found in the periphery16, the changes on the visual quality promoted by the defocus alone might be subtle and not high enough to be perceived by the visual system18. So, defocus alone might not explain why those contact lenses deter the progression of myopia19.
Two main hypotheses may still grant to a certain extent a role to defocus in the progression of myopia. The first one proposes the conflict in the spatially oriented ganglion cells20,21,22,23 and its selectivity that can act as myopigenic clues24. Thus, eye growth might be prompted in case a large anisotropy is present in the periphery25, and the underlying mechanism of multifocal contact lenses may be related to a reduction of the ratio of radial to azimuthal contrast25. Nonetheless, this anisotropic or directional blur has been reported to match neuronally, suggesting a coupling between the two systems25,26,27,28,29. Thus, this hypothesis can not explain why some contact lenses still report some effect slowing myopia even after two years of wear7,30. Meanwhile, another hypothesis suggests that the ebb in the image quality might be a possible indicator for the retina to react to the presence of blur, deploying signals that are related to the growth of the eye30. Nowadays, wave-front technologies allow us to recompose refractive errors and aberrations of the eye at different eccentricities31 and thus, image quality metrics can be computed readily across the visual field.
In this study, the image quality metrics while wearing contact lenses are mapped and estimated for a visual field of 20 degrees surrounding the fovea. The visual field is segmented for further analysis, and the possible implications of the image quality crumble through multifocal contact lenses are discussed in detail.
The core findings are split into three main groups: (A) the analysis of the root mean square errors (RMSE), where a single number reports the differences against the achievable limit for each image quality conditions, (B) the full-field data-sets analysis, where all the points from the maps were analysed, and finally (C) the sub-analysis by regions and groups (peripheral refractive patterns and optical states), where points are analysed by taking into account their location and the refractive pattern of the subject.
Currently, several optical treatments have shown a reduction in the progression of myopia, but the underlying mechanisms on which these treatments rely, still, remain unclear. As one theory supports the influence of the peripheral refractive error of the eye, the current study obtained similar results as reported earlier32,33. Looking beyond peripheral refraction, a global approach describing the retinal defocus patterns34 can explain the inter-subject variability regarding the efficacy of myopia interventions2. While the question remains, as to how the retina distinguishes lower order as well as higher order aberrations, a more in-depth analysis of the full image quality is required. Indicators that allow describing the image quality with such treatments will then, facilitate the understanding of the progression of myopia or the development of more efficient optical treatments to control the progression of myopia.
Estimation of the spatial frequency limit. (A) Surface plot of the function, plus the dataset from different studies included. (B) Representation of the reference image through a low-pass filter that restricts to the spatial frequency limit on each retinal location. For display purposes herein, only the foveal and 20 NTSI (nasal/temporal/superior/inferior) eccentricities are imaged.
Shows the image quality across the visual field for one subject while wearing (A) no lens correction, (B) a multifocal contact lens with centre-near design and (C) a centre-distance contact lens design. It also shows the differences that these optical conditions caused to the image quality limit.
Image quality metrics were computed across a large visual field, not only for the naked eye but additionally for two different optical designs of multifocal contact lenses. Other authors have published prior work on image quality and contact lenses18,35,36,37, but to the best of our knowledge, this study reports for first-time results for a wider visual field (not only the horizontal meridian) and relies on real aberration measurements rather than theoretical simulations18.
In congruence with the published literature38,39, results indicate that image quality across the visual field is reduced when multifocal contact lenses are worn. However, the overall results presented some inconsistencies, depending on the analysis. On the one hand, with the RMSE full-field comparison, the image quality from the naked eye did not decay significantly when the multifocal centre-distance design was present. In contradiction, and when analysing the local or full-field grouped data, this optical design of the contact lens did promote significant differences against the naked eye.
Results of the RMSE, where only the centre-near design deteriorate the image quality, cannot explain why several authors found that centre-distance contact lenses show a better efficacy on the control of myopia progression40,41. Nonetheless, when assessing a more detailed test, the centre-distance design seemed also capable of promoting differences in every peripheral refractive group, except for the positive temporal skew (PTS) pattern. The absence of significant changes in this group might be the underlying reason why the RMSE comparison failed to find significant differences.
In the grouped/ranked analysis, the mean of the groups did not present differences between centre-near and centre-distance, which precludes from concluding that there are high differences in the reduction of image quality between contact lenses. The regional analysis of the different optical solutions indicated that the inferior field might be the main contributor for the non-significant changes between the different contact lens designs (as in the full-field analysis). Although no pattern can be established in the pairwise regional differences between peripheral refractive groups, it appears that image quality worsens on a similar manner for relative peripheral hyperopia (RPH), relative peripheral myopia (RPM) and positve nasal skew (PNS) groups in the central area (0 to 5 degrees). Namely, the positive nasal skew (PNS) and the relative peripheral myopia (RPM) full inferior visual field presented a similar behaviour. Contrarily to the pure defocus analysis34, the deterioration of the image quality when contact lenses are worn, does not seem to rely on the skewness of the peripheral refraction. Only PTS (positive temporal skew) appears to overtake the optical treatments and be less receptive to changes produced by multifocal centre-distance lenses. 59ce067264