The current study shows the evolutions of aberrations in the eye and in the anterior cornea of children corrected with dual-focus CL and single-vision spectacles. As measures were obtained after take-off the optical compensation the novelty of this work is centered in study of structures/ tissues dynamics in adaptation or response to different optical compensations.
Other studies previously have evaluated the aberrations and the light disturbance induced by wearing CL designed for myopia control.22, 32 Center-distance design MFCL, which were previously considered favorable to myopia control by producing peripheral relative myopia, were evaluated by several authors such as Fedtke et al.33 MFCL were shown to significantly induce positive shifts in primary SA (4th order SA), whose absolute value increased according to the increase of pupil size and add power. Dual-focus designed lenses also produced positive SA in 3 mm pupil size, but conversely, in greater pupil sizes of 4 mm, a higher negative value of 4th order SA was found, and even more so in the 5 mm pupil size. These findings show that the changes in HOA induced by dual-focus designs (such as MiSight) are substantially more pupil-dependent than the center-distance MFCL designs31, 34 and shows the role of SA whose magnitude differently affects the myopia control.34
Previous MASS studies have also reported an increase on monocular light disturbance perception28 and near-vision worsening26 in subjects wearing MiSight (study group) compared with subjects wearing single-vision spectacles (control group). Nevertheless, over 2 years of follow-up there could be seen a significant binocular attenuation effect, and a consequent decrease in the monocular light disturbance. Fernandes et al.35 did not find significant differences between manifest light disturbance in presbyopes after 15 days in participants who had been wearing Biofinity MF compared with monovision CL. In addition, there were no signiﬁcant changes in the Quality of Vision questionnaire between different CL modality, suggesting an objective and subjective adaptation to multifocality over time. Another previous study also found satisfactory high-contrast distance and near visual acuity (VA) (LogMAR about 0.00 or better) with both lens modalities (monovision and MFCL) being highly comparable with the best corrected VA in spectacles at both long and short distance.36
In the present study, contrary to other studies, we performed measurements on the condition of the naked eye. For this reason, we were able to perceive the changes at the HOA level promoted by changes occurring in the eye, essentially through the influence of CL in the cornea and by the axial elongation during the myopia progression (with and without influence). The data shows that after 2 years, the ocular axial length significantly increased in both groups; the LO_RMS_T and HO_RMS_T only significantly increased in the control group as the AL increased 0.160 mm more than in the MiSight study group (0.45 D vs 0.74 D), confirming the influence of the increase of myopia (promoted by axial elongation) in RMS especially promoted by LO_RMS, since HO_RMS did not change significantly over 2 years.
There have been several previous studies regarding the relation between HOA and refractive error. In a recent review, Hughes et al.34 considered this topic to be controversial and Little et al.12 thought it to be due mainly asymmetries in sample size, differences in subjects’ age/ethnicity, or varying methodological procedures, including differences in classification of refractive error. Despite this, most studies37, 38 show that HOA values are higher in myopes than emmetropes or hyperopes, and there is a correlation between primary SA (4th order) and refractive error in such a way that value of 4th order SA in the eye becomes less positive with increasing myopia and axial length.13 Contrary to results from the literature, the present study did not reveal significantly changes in SA of the eye during the 2-year period of evaluation, during which myopia progressed asymmetrically in both groups. Despite differences in terms of axial elongation between the groups studied, none showed tendency to SA values becoming less negative over the 2 years. These findings indicate that the SA of the eye (SA_T) firstly evolved differently with AL growth in our sample compared with other larger Asiatic samples13, and secondly the greater fluctuation occurred in the control group throughout the evaluation, although there were no significant differences.
The baseline myopia of the subjects allocated to the MiSight group was slightly higher (p > 0.05) than in the control as these subjects were older (p < 0.05); for this reason, we have in the MiSight group slightly longer eyes, higher RMS_T and more positive SA_T (p > 0.05 to all). Considering the findings from Little et al.12, this group, by having longer eyes, should present less positive values for primary SA, which was not verified in the study. With regard to axial length, however, at the end of 2 years, differences between the groups had already become significant (p < 0.05), the axial length in the control group being 0.160 mm longer and the value of SA less positive. Another important aspect concerns the tendency to increase the axial length/myopia shift according to the basal SA of the eye13, 39; our results reversely to other studies showed that it is not clear the correlation between high positive SA values and low myopic shift actually occurred in the MiSight group.
In the current study, the axial elongation retention rate at 2 years was 36%27 lower than that found in another recent study with a similar methodology (53%).40 However, this asymmetry can be explained in relation to differences in age/AL among the groups at baseline as explained above.
The center-distance MFCL and orthokeratology,41 by reducing the peripheral hyperopia, produce positive SA42 that is known to be effective in myopia retention, and is inducted by contact lenses.43 The present study looked at different changes in aberrations in myopic children treated with dual-focus MFCL vs spectacles. If, on the one hand, it is known that different commercially available designs of MFCL worn on the eye differently affect the magnitude of the peripheral refraction and SA profiles along different visual field meridians,44 on the other hand, it is certain that its effectiveness depends on multiple factors as the inherent aberration/SA, the age and the pupil size present in the eye at the beginning of treatment.
At corneal level, no significant changes were seen suggesting that the wearing of MiSight in children’s eyes did not produce any influence on corneal shape, resulting in no changes in corneal aberrations, even after 24-months of daily use of approximately 11 hours per day, 6 days per week.27 The safety and acceptance of MiSight has already been evaluated45 over 3 years and does not report significant adverse events in children between 8 and 12 years old.40 Hiraoka et al.46 recently found a significant correlation between myopia progression/axial elongation and many components of corneal HOA. Our results indicate corneal HO RMS to be around 0.296 ± 0.307 µm and 0.278 ± 0.247 µm at baseline respectively in the control and MiSight groups; these values are low, and according to the same study46, a high change in axial length must be expected. Throughout the 2 years of this study, no differences in either group were found indicating that corneal HOA and SA did not substantially influence the regulation of myopia progression over time; nor were they significantly affected or regulated by dual focus MFCL approach to myopia management.
In conclusion, this study shows no differences between the inherent total and corneal aberrations in children who have been using dual-focus MFCL and single-vision spectacles over 2 years. However, the results show an increment in low order aberrations in the control group that was due the higher myopia progression and axial elongation seen in this group and reported in previous MASS study.