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Abstract
Multifocal contact lenses are increasingly popular interventions for controlling myopia. This study presents the short-term effects of multifocal contact lenses on foveal and peripheral vision. The MiSight contact lenses designed to inhibit myopia progression and the 1-Day Acuvue Moist contact lenses designed for presbyopia were investigated. The MiSight produced similar foveal results to spectacles despite the increased astigmatism and coma. The MiSight also reduced the low-contrast resolution acuity in the periphery, despite no clear change in relative peripheral refraction. When compared with spectacles, Acuvue Moist decreased accommodative response and reduced foveal high- and low-contrast resolution acuity, whereas peripheral thresholds were more similar to those of spectacles. The most likely treatment property for myopia control by the MiSight is the contrast reduction in the peripheral visual field and the changed accommodation.
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. INTRODUCTION
The prevalence of myopia has increased rapidly worldwide over the last years, and, according to the World Health Organization (WHO), 50% of the world’s population will be myopic and 10% highly myopic by 2050 [1]. Myopes have an increased risk of developing myopic maculopathy [2], retinal detachment [3], cataract [4], and glaucoma [5]; thus, there is growing need to decrease myopia progression. Studies have found a relation between the early onset of myopia and high myopia in adult life [6,7]; therefore, it is important to control and halt the progression of myopia at a young age. Although not yet well-understood, two often-mentioned environmental causes for myopia progression are peripheral image quality and lag of accommodation.
It was originally believed that only foveal optical errors controlled eye growth, but animal studies have shown that the peripheral retina is also important for eye growth regulation; peripheral image quality can modify ocular growth even in the presence of a clear foveal image [8,9]. Based on many animal studies, two hypotheses are presented in regard to the effect of peripheral vision in myopia. The first is that peripheral hypermetropic defocus in the human eye can accelerate eye growth; the second is that optical corrections that either eliminate peripheral hypermetropic defocus or produce myopic peripheral defocus can slow the progression of myopia [10–13]. Another suggested cause of myopia is based on the associations found between underaccommodation and increased rate of myopia progression. With negative power lenses or when viewing nearby targets, the eye often accommodates less than what is needed to bring the target into focus. This underaccommodation is referred to as lag of accommodation (hypermetropic retinal defocus). Larger lag of accommodation during near work has been associated with the development and progression of myopia [14,15]. Furthermore, myopic children and young adults show greater variability in accommodative response, reduced accommodative facility, and enhanced accommodative convergence (elevated AC/A ratios) when compared with age-matched emmetropes [16].
Many different interventions, including pharmaceutical and optical methods, now aim to control myopia progression: Atropine in low concentration [17]; Orthokeratology rigid contact lenses [18–20]; bifocals and progressive addition spectacles [21–23]; multifocal soft contact lenses. This study concentrates on multifocal contact lenses, an increasingly popular myopia intervention method. The principle of this intervention is that a center distance (CD) design controls the progression of myopia by presenting two simultaneous images, i.e., one image focused on the retina and one in front of the retina to create a myopic blur, while looking at a distant target with relaxed accommodation. However, such multifocal designs will cause large irregular optical aberrations in peripheral angles that may affect the depth of focus more than does the peripheral refractive error [24]. Furthermore, the effective properties of these lenses are not yet well known, and the treatment effect varies between individuals [24]. This could be because multifocality can affect the level of accommodation and the foveal and peripheral image quality in young myopic eyes [24–27]. Several previous studies have investigated the effect of one commercially available CD contact lens design (i.e., MiSight) on foveal optics, vision, and accommodation; however, the results were not compared with those of peripheral effects [28–30]. It is thereby difficult to know whether the reduced myopia progression with these multifocal lenses is because of their effect on accommodation or on peripheral image quality. Therefore, this study will investigate the short-term effects on accommodation and on foveal and peripheral optical and visual quality by MiSight multifocal contact lenses. The aim is to unravel the effect on accommodation and on peripheral image quality of these lenses compared with ordinary spectacles, also incorporating foveal and peripheral wavefront aberration data collected during vision evaluations. To identify changes in properties that are specifically linked to myopia control, the same measurements were also performed with a popular multifocal contact lens with the opposite design, i.e., center near (CN), used for presbyopia (Acuvue Moist).
Table 1. Subjectsa
2. METHODS
A. Subjects and Contact Lenses
Eight myopes with refractive states between ${-}{1.50}$ and ${-}{7.00}$ diopters (D), aged between 22 and 40 years old, participated in this study (more details in Table 1). All subjects had good ocular health and were experienced contact lens users. The subjects underwent measurements divided in to two parts: (1) monocular clinical accommodation evaluations; (2) monocular low-contrast vision evaluations, with three different types of optical correction measured in the following order:
- (a) their habitual spectacles (control)
- (b) MiSight 1-day (CooperVision)
- (c) Acuvue Moist 1-day (Johnson & Johnson)
The MiSight contact lens is a multifocal contact lens with a center-distance (CD) design with ${+}{2.00}\;{\rm{D}}$ treatment zones. It corrects the myopic refractive error while simultaneously presenting a myopically defocused image; it has also been proven to slow the progression of myopia in children [28–30]. The power profile of a MiSight contact lens with a nominal power of ${-}{3.00}\;{\rm{D}}$ is shown in Fig. 1.
Fig. 1. Power profile of the MiSight contact lens for myopia control. The presented contact lens has a nominal power of ${-}{3.00}\;{\rm{D}}$. The horizontal bands indicate 1.00 D steps. Adopted from Ruiz-Alcocer [46].
The Acuvue Moist contact lens is a multifocal contact lens with a center-near design (CN) used for presbyopia correction. It corrects myopia or hypermetropia while providing clear near vision due to the additional power offered by the lens profile. The Acuvue Moist multifocal contact lens is available in low, mid-, and high adds; it is also a smooth design with progressively more negative power when moving radially from the center out toward the edges of the lens. In this study, the used lens had a high add of ${+}{2.50}\;{\rm{D}}$.
The fitting of the contact lens was checked with a slit lamp according to clinical standard to ensure that the lens was sitting properly on the subject’s eye before starting the measurements. A few minutes were given to the subjects to adapt to the contact lens, and the measurements started when the subjects felt comfortable. Natural pupils were used throughout the measurements. Prior to experiments, written informed consent was obtained from the subjects. The study was approved by the Swedish Ethical Review Authority and conformed to the tenets of the Declaration of Helsinki.
B. Clinical Visual Function and Accommodation Evaluation
For clinical visual function and accommodation evaluation, each of the three optical corrections was applied one at a time on the tested eye, and the following measurements were taken monocularly (the fellow eye was covered with an occluder):
- • Distant and near high-contrast letter visual acuity (VA)
- • Near point of accommodation (NPA)
- • Accommodative facility (AF)
- • Accommodative response (AR)
The majority of the tests (near VA, NPA, AF, AR) were performed under standard room illumination (700 lux), except the distant VA test, which was performed under slightly dim light (300 lux).
The subjects were evaluated for their monocular foveal distant (4 m) visual acuity with a high-contrast EDTRS visual acuity chart with letter sizes from 1.0 to ${-}{0.3}$ logMAR. For monocular foveal near-vision evaluation, a near-visual-acuity high-contrast EDTRS chart was used at 0.4 m distance. The subjects were asked to read the letters on the chart line-by-line until they were unable to recognize the letters.
A Royal Air Force (RAF) ruler was used for monocular foveal NPA estimation; Donder’s push-up and pull-away tests were performed.
Monocular foveal accommodative facility was measured by ${{\pm 2}.{00}}\;{\rm{D}}$ flipper. The test was performed under standard room illumination for 30 s, while the subjects were holding a near-vision acuity EDTRS chart at 0.4 m distance and had to focus on a row slightly larger than their best vision.
The Shin Nippon Natural Vision Auto Refractometer NVISION-K 5001 was used for monocular foveal AR measurements. Refraction measurements were performed first with the subject looking at a nonaccommodative target at 4 m and second when looking at a target 0.4 m from the eye. The AR was determined as the difference between the spherical equivalent at 4 m minus the spherical equivalent at 0.4 m. Additionally, astigmatism was converted to power vectors by using the equations derived by Thibos et al. [31].
The duration of the clinical accommodation evaluation was around 1.5 h. Regular breaks were taken to avoid fatigue; all measurements were repeated thrice, and the average values were used for analysis.
C. Evaluation of Image Quality and Low-Contrast Vision
The second part of the experiment was performed in a laboratory adaptive optics (AO) setup with a Hartmann–Shack (HS) wavefront sensor, a deformable mirror, and a monitor for stimulus presentation. During the experiment, the HS wavefront sensor recorded the pupil size as well as the foveal and peripheral wavefront data live for further image-quality analysis. The AO system operates in near-infrared light but is calibrated to measure in visible light. The AO system consists of the HASO wavefront sensor and the Mirao 52 D deformable mirror (52 actuators, ${{\pm 50}}\;{{\unicode{x00B5}{\rm m}}}$ stroke, corrects up to sixth Zernike order, https://www.imagine-eyes.com), which was set to static compensation only for the internal aberrations of the AO system (i.e., the AO part of the system was not running in closed loop during the experiment). Details of the system have been earlier described by Rosén et al. [32].
Monocular low-contrast (10%) resolution acuity measurements were performed for all three conditions (a, b, c; beginning of the Methods section) foveally as well as at 20° nasal visual field. The subjects were fixating on a Maltese cross mounted 2.6 m away, while peripheral acuity thresholds and wavefront aberrations were measured on their right or left eye with natural pupil sizes. A chin-forehead-rest was used for stability, an infrared camera was used for alignment, and the HS sensor of the AO system was used to monitor the subject’s fixation throughout the experimental procedure. If necessary, the subjects were realigned in order to obtain a full and sharp pupil image.
The psychophysical procedure to obtain the low-contrast resolution thresholds was implemented in MATLAB and Psychophysics toolbox, following the same process as described earlier [33]. The low-contrast resolution acuity task was chosen because it is limited by optical properties and not by the neural sampling also in the periphery [34,35]. The stimulus pattern consisted of low-contrast (10%) oblique (${-}{{45}}^\circ$ and 45°) Gabor gratings in a Gaussian window with a standard deviation of 1.6°. The oblique orientation of the gratings was chosen in order to avoid any neural preferences due to the meridional effect [36]. Additionally, the size of the displayed gratings was adjusted to compensate for the spectacle magnification. Bayesian psychophysical procedures were used to vary the spatial frequency of the gratings and measure the acuity thresholds. The stimuli were presented for 500 ms on a calibrated CRT monitor 2.6 m away from the subject; further, the subject had to identify the orientation of the gratings in a two-alternative forced choice paradigm. A sound cue was played in the beginning of each trial to ensure that the subject was aware of the stimulus presentation. The subject then had to press the corresponding key on a keypad according to the orientation of the gratings. When the stimulus could not be resolved, the subject was instructed to guess; guess rate and lapse rate were set to 50% and 5%, respectively. No feedback was given to the subjects whether they were responding right or wrong, and the acuity was determined in 40 trials. All measurements were repeated three times, and the average acuity values were used for further analysis. Every third set (or more often if needed), the subjects would rest to avoid fatigue. Before the actual experiment, a test round was performed to ensure that the subject understood the routine. The duration of the second part of the experiment with low-contrast vision evaluation was almost 1.5 h per subject.
D. Data Analysis
Wilcoxon paired-samples two-tailed signed rank tests were conducted to compare the multifocal contact lenses with spectacles (control).
Bar plots were used to show the individual data whereas box-and-whiskers plots were used to show the distributions of the data. In the box-and-whiskers plots, the center black line represents the median, the edges of the box represent the interquartile range, the whiskers represent the data outside the middle 50%, and the dots represent the outliers.
3. RESULTS
The short-term effects on foveal and peripheral vision of the MiSight and the Acuvue Moist multifocal contact lenses were evaluated. It should be noted that, during the experiments, several subjects spontaneously expressed that MiSight was clearly less comfortable compared with Acuvue Moist both in fitting and in visual quality.
In the following bar plots, the subjects are sorted according to their accommodative response with spectacles (from minimum accommodative response to maximum accommodative response).
Fig. 2. Foveal monocular distant (4 m, top) and near (0.4 m, bottom) letter visual acuity in logMAR. The bars are not visible for Subject 6 (top left graph) and Subject 1 (bottom left graph), as they correspond to 0 logMAR.
Fig. 3. Monocular near point of accommodation in cm as estimated from the Donder’s push-up test (left) and monocular accommodation facility in cycles/minute as measured by ${\rm{\pm 2}.{00}}\;{\rm{D}}$ flipper (right).
Fig. 4. Monocular accommodative response in diopters as measured with an open-field autorefractor. The accommodative response is determined as the difference between the spherical equivalent at 4 m minus the spherical equivalent at 0.4 m.
Fig. 5. Monocular change in cylinder with accommodation in diopters as measured with an open-field autorefractor. The change in cylinder with accommodation is determined as the difference between the cylinder at 4 m minus the cylinder at 0.4 m. Positive sign means an increase in cylinder; negative sign indicates a decrease. The nonvisible bars for Subjects 3 and 7 correspond to 0 D.
A. Clinical Visual Function and Accommodation Evaluation
- • Distant and near letter visual acuity
The monocular foveal letter VA values for distant (4 m) and near (0.4 m) vision are given in Fig. 2. For distant VA, there was no statistically significant difference ($p \gt {0.05}$) between the MiSight lenses and the control case, whereas the difference between the Acuvue Moist lenses and the control case was statistically significant ($p \lt {0.05}$), as expected; Acuvue Moist lenses are used for presbyopia correction and the positive addition (${+}{2.50}\;{\rm{D}}$) degraded the distant vision of the subjects by 0.20 logMAR on average. For near vision, there was no statistically significant difference ($p \gt {0.05}$) neither for MiSight versus control nor for Acuvue Moist versus control.
- • Near point of accommodation and accommodative facility
In Fig. 3, the monocular NPA (in cm from the eye) and the accommodative facility (in cycles/minute) are presented. For NPA, no statistically significant difference ($p \gt {0.05}$) was found when the subjects were wearing their spectacles compared with when they were having contact lenses. For accommodative facility, there was no statistically significant difference ($p \gt {0.05}$) between the MiSight design and the control. However, there was a statistically significant difference ($p \lt {0.05}$) when the control case was compared with the Acuvue Moist multifocals.
- • Accommodative response
Figure 4 presents the change in accommodative response measured with an open-field autorefractor. The accommodative response is determined as the difference between the spherical equivalent at 4 m minus the spherical equivalent at 0.4 m. The Acuvue Moist design decreased the accommodative response by 1.00 D (statistically significant difference, $p \lt {0.05}$) on average when compared with the control, and the MiSight design increased the accommodative response in six out of the eight subjects compared with the control but not at a significant level.
Both multifocal designs induced astigmatism when measured in the autorefractor. The MiSight lenses increased the cylinder in all subjects, whereas Acuvue Moist lenses increased the cylinder in five out of eight subjects when compared with the control at 4 m, with an average increase of 0.75 D and 0.25 D, respectively. There was also a change in cylinder with accommodation, as shown in Fig. 5. The change is determined as the difference between the cylinder at 4 m minus the cylinder at 0.4 m, ignoring any change in the axis of the cylinder; a positive sign means an increase in cylinder with accommodation, whereas a negative sign indicates a decrease. For six of the eight subjects, the cylinder increased with accommodation up to approximately 1.50 D with MiSight lenses, whereas the Acuvue Moist lenses showed smaller cylinders for most of the subjects.
Table 2. Wilcoxon Paired-Samples Two-Tailed Signed Rank Tests in Astigmatism (Power Vectors)a
Fig. 6. Foveal and peripheral (20° nasal visual field) monocular low-contrast (10%) resolution grating acuity thresholds in logMAR.
For statistical analysis, the measured astigmatism from the autorefractor was converted to power vectors; differences in astigmatism were tested with Wilcoxon paired-samples two-tailed signed rank tests. Table 2 presents the tested differences as well as the results of the statistical tests. The MiSight lens showed significantly more negative values compared with the control for three out of four cases.
B. Low-Contrast Vision Evaluation
Figure 6 presents the low-contrast (10%) resolution grating acuity thresholds for foveal and peripheral (20° nasal visual field) far vision. The MiSight contact lenses reduced the foveal resolution acuity by 0.05 logMAR when compared with control, although the difference was not significant ($p \gt {0.05}$). With the Acuvue Moist the reduction in foveal vision was significant ($p \lt {0.05}$) and on average 0.13 logMAR less than the control.
The peripheral thresholds were decreased significantly ($p \lt {0.05}$) with the MiSight lenses by 0.10 logMAR when compared with spectacle correction, whereas the thresholds for Acuvue Moist were similar to those of the control case.
C. Wavefront Analysis
Figure 7 shows the largest foveal and peripheral Zernike coefficients (except for defocus) for 4 mm pupil diameter for the three optical correction conditions. Because the right and the left eye are mirror symmetric for on- and off-axis aberrations, the signs of the coefficients for oblique astigmatism and horizontal coma were changed for the subjects that had their left eye measured [37]. Wilcoxon tests were performed on the differences between the conditions (control-MiSight, control-Acuvue Moist), with foveal horizontal coma showing a statistically significant increase for MiSight lenses (${{\rm{T}}_ -} \le {{\rm{T}}_{0.10(2),8}},\;p \lt {0.10}$), and peripheral vertical astigmatism showing a decrease both for MiSight and Acuvue Moist (${{\rm{T}}_ +} \le {{\rm{T}}_{0.10(2),8}},\;p \lt {0.10}$).
Table 3 presents the relative peripheral refraction (RPR) of the subjects averaged over time separately for the three conditions. The RPR is defined as the difference between the peripheral refractive error minus the foveal refractive error. The refractive error was calculated from the wavefront using second- (defocus), fourth- (spherical aberration), and sixth- (secondary spherical aberration) order Zernike coefficients with natural pupil size. Negative values indicate a more myopic periphery, whereas positive values indicate a more hypermetropic periphery relative to the fovea. There was no statistically significant difference between the MiSight lenses and the control ($p \gt {0.05}$), but there was a statistically significant difference between the Acuvue Moist lenses and the spectacles ($p \lt {0.05}$).
D. Foveal and Peripheral Image Quality
The foveal and peripheral (20° nasal visual field) modulation transfer functions (MTFs) were calculated for all subject and conditions from the wavefront data gathered during the low-contrast vision evaluation. The MTFs were obtained for natural pupil size at $\lambda = {{550}}\;{\rm{nm}}$. For peripheral measurements, the elliptical shape of the pupil was taken into account using a cosine function [38]. Figure 8 shows the median versus maximum MTF values of Subject 5. Generally, for all subjects except Subject 4, the control case showed the best foveal MTF, followed by Acuvue Moist, followed by MiSight, which produced the worst foveal MTF. This trend was less clear in the periphery.
Table 3. Relative Peripheral Refraction (RPR)a
Fig. 8. Monochromatic foveal and peripheral (20° nasal visual field) modulation transfer function (MTF) curves for natural pupil size for Subject 5. The plotted curves represent the median (solid line) versus the maximum (dotted line) MTF values.
4. DISCUSSION
This study investigates the short-term effect on foveal and peripheral vision of two multifocal contact lenses. The aim is to document changes in accommodation and in foveal and peripheral image quality since these properties are thought to be linked to myopia progression. The results were compared with those of spectacles, since spectacles are the most common correction for myopic children.
When compared with spectacles, MiSight contact lenses produced similar foveal visual quality for far and near, whereas the peripheral low-contrast resolution acuity was significantly decreased. Accommodative response was increased in six out of eight subjects with MiSight lenses, whereas accommodative facility and NPA tended to be worse. Astigmatism at far and near and foveal coma were increased for all subjects. Acuvue Moist multifocals showed almost the opposite results: they significantly decreased the foveal visual quality for far when compared with spectacles, whereas foveal VA at 0.4 m and peripheral low-contrast resolution acuity were similar to those of spectacles. Accommodative response and facility were significantly reduced, but the astigmatism was similar to control both at far and near. It is worth mentioning that the Acuvue Moist was the last lens to be tested and showed reduced foveal letter VA at 4 m despite any potential learning effects.
In a previous study, Ruiz-Pomeda et al. found no statistically significant difference in the amplitude of accommodation between the MiSight group and the single-vision spectacles (MiSight: ${13.88}\;{{\pm}}\;{3.58}\;{\rm{D}}$, spectacles: ${12.40}\;{{\pm}}\;{2.55}\;{\rm{D}}$). In the same study, the accommodative response at 0.33 m for MiSight (${1.08}\;{{\pm}}\;{0.61}\;{\rm{D}}$) was also similar to the single-vision spectacles (${1.24}\;{{\pm}}\;{0.75}\;{\rm{D}}$) [28]. Gifford et al. compared accommodative responses at five distances of young myopes wearing single-vision contact lenses and four different multifocal contact lens types for myopia control (including MiSight lenses). The authors found similar accommodative responses between single-vision and MiSight contact lenses (slopes: ${1.01}\;{{\pm}}\;{0.06}$ and ${0.96}\;{{\pm}}\;{0.15}$, respectively), whereas the slopes for the rest of the multifocal designs were approximately ${0.84}\;{{\pm}}\;{0.15}$ [39]. The results of the current study are in agreement with Ruiz-Pomeda et al. and Gifford et al.; MiSight lenses showed no significant difference neither in the NPA nor in the accommodative response. Also, it was found that the MiSight contact lenses produced similar distant and near foveal VA when compared with control; consistent with the previous findings from Ruiz-Pomeda et al. and Chamberlain et al. [30].
Sha et al. compared the visual performance of four different contact lens designs for myopia control, including MiSight. The authors found that subjects wearing MiSight lenses achieved significantly worse monocular accommodation facility when compared with two of the other designs (Prototype 1 and Prototype 2). In the current study, although not statistically significant, accommodation facility with MiSight was worse than with spectacles (MiSight ${12.8}\;{{\pm}}\;{{5}}\;{\rm{cycles/minute}}$, spectacles ${15.3}\;{{\pm}}\;{{5}}\;{\rm{cycles/minute}}$) but still better than the finding of Sha et al. (MiSight ${11.7}\;{{\pm}}\;{4.8}\;{\rm{cycles/minute}}$) [29]. In the same study, the subjects assessed the four different designs and reported better visual performance and ocular comfort with Prototype 1 and Prototype 2 when compared with MiSight. In the current study, likewise, all subjects reported visual disturbances with MiSight lenses, something that was not reported when the Acuvue Moist lenses were applied. Specifically, the subjects reported discomfort, reduced contrast, and slightly compromised near vision with ghost images. However, this could be due to the fact that the subjects did not have the time to adapt to the optics of MiSight lenses. Despite the discomfort, the MiSight lenses did not reduce the foveal visual quality of the subjects when compared with spectacles. An explanation for this might be that the MiSight lenses reduce contrast for such low spatial frequencies that the foveal low-contrast resolution acuity measurements were not affected.
Bakaraju et al. found differences in J0 and J45 when the COAS-HD aberrometer (HS sensor principle) and the Shin-Nippon autorefractor were compared for multifocal contact lenses measurements. For J0, the authors found that the COAS-HD produced more positive measurements for the CN designs, whereas the autorefractor measures were more positive with the CD design. For J45, they found mean differences ranged between 0.10 D and 1.50 D within both the instruments [40].
In the current study, the wavefront aberrations and the MTF curves were measured continuously during the low-contrast vision evaluation. Therefore, in the absence of long-term vision adaptation, the average changes in the MTFs for different conditions ought to correspond to the observed trend in low-contrast vision. Although this was true on the qualitative level, we did not find a direct quantitative correspondence between the MTF and the logMAR values obtained from the psychophysical procedures, neither for the fovea nor the periphery. Although previous work suggests that Hartmann–Shack wavefront sensors can measure lower- and higher-order aberrations on multifocal contact lenses accurately enough [41], artifacts such as spots-doubling on the border of the multifocal contact lens zones make the analysis more challenging [42]. To investigate the correctness of the MTF curves, additional foveal and peripheral wavefront measurements on subjects S4 and S7 were performed in a lab-based dual-angle system where the accuracy of the wavefront reconstruction could be verified manually [43]. No artifacts were spotted in these verification measurements, and the changes in the MTF curves for the different optical conditions were similar to those recorded in the adaptive optics system. We thereby concluded that the wavefront measurements are accurate and that the lack of a direct quantitative correspondence might be due to the fact that the wavefront was recorded continuously over time and not only when the Gabor gratings were presented to the eye.
A. Possible Properties for Myopia Control
Animal studies suggest that myopic peripheral blur can reduce eye growth; it is believed that peripheral image quality is also linked to myopia in humans [8,9,11,13]. Previous studies have reported a treatment effect with MiSight contact lenses for myopia control in children [28,30]. Although the current study has been performed on a relatively small sample size of adults, its results show that this contact lens changes three properties of the image quality that might be related to myopia control.
The first and most likely property of MiSight lenses is the contrast reduction in the peripheral visual field. The wavefront measurements did not show any clear difference in RPR (see Table 3) between the MiSight and the spectacles, despite the large effect on peripheral vision. Thus, the observed contrast reduction in the peripheral visual field was not caused mainly by defocus but by a more complicated higher-order aberrations pattern. However, these higher-order aberrations not only reduce the contrast in the peripheral image, they also increase the depth-of-focus. We therefore believe that it could be more efficient with a myopia control intervention that takes into account the peripheral optical errors of the individual eye. This can render a smaller depth-of-focus and hence produce large contrast reductions also for lower magnitudes of RPR. The second property for myopia control may be the additional astigmatism with the MiSight lenses; higher astigmatism and coma lead to a more asymmetric point spread function, which may be used by the eye to easier detect the location of the image with respect to the retina. The third possible property could be the larger accommodative response shown by some of the subjects in this study (see Fig. 4); it cannot be determined, however, whether it is because of a smaller accommodative lag for near or a larger accommodative lead for far with the MiSight lenses. However, it is concluded that the zones with additional power in the MiSight lens are not used as “reading-glasses” by the eye during near vision; if they had been used, the accommodative response would have look more like that of the Acuvue Moist lenses.
In the context of myopia control, it is also important to note that the same multifocal contact lens can have different treatment effect in different individuals. For example, the treatment zones of MiSight lens will not have the same impact on individuals with small pupils or in bright light conditions when compared with individuals with larger pupils or in darker conditions. This is illustrated in Fig. 9 by the peripheral (20° nasal visual field) Hartmann–Shack spot diagrams of Subject 4 with the contact lenses; MiSight lens on the left side and Acuvue Moist on the right. In the MiSight case, the zones of the lens are clearly visible, whereas Acuvue moist shows a more uniform profile (the nonuniformity at the right edge of the picture is because of the optical-zone edge of the lens). This is due to the fact that MiSight lens has a more distinct profile with alternating distance and near zones, whereas Acuvue Moist has a more gradual change in power between near and distance zones [44].
Fig. 9. Spot diagrams at 20° nasal visual field of Subject 3 as obtained from the Hartmann-Shack sensor during the experiment. The MiSight lens is on the left side and the Acuvue Moist on the right side with 7.5 mm and 6.7 mm in average pupil size, respectively.
5. CONCLUSION
The short-term effect on foveal and peripheral vision of two multifocal contact lenses was measured; 1) the MiSight 1-day center-distance (CD) contact lens (treatment zones ${+}{2.00}\;{\rm{D}}$, CooperVision) and 2) the Acuvue Moist 1-day center-near (CN) contact lens (high add ${+}{2.50}\;{\rm{D}}$, Johnson & Johnson). In summary, MiSight contact lenses differed from spectacles with more astigmatism and coma, worsened peripheral low-contrast resolution acuity, and increased accommodative response. These differences may be the myopia control properties of the MiSight lens. It is noteworthy that the reduced peripheral low-contrast vision with the MiSight lenses was not because of a more myopic RPR, which is the common belief about the effect of these lenses. The Acuvue Moist lenses did not show the same differences; they produced similar astigmatism and peripheral vision as the spectacles, more hypermetropic RPR, and decreased foveal vison and accommodative response. In spite of this, subjects reported Acuvue Moist as being more comfortable than MiSight. The most likely treatment property for myopia control by the MiSight is the contrast reduction in the peripheral visual field and the changed accommodation. It is interesting to note that the magnitude of the induced peripheral blur is not caused by pure defocus but is still large enough to reduce peripheral visual function even more compared with the already quite poor peripheral image quality produced by the off-axis angle through the spectacles and the natural optics of the eye [45]. A reduction in peripheral image quality on such a scale may hamper daily tasks involving peripheral vision, such as detection, orientation, and locomotion. The results may be important in the quest of understanding and improving myopia control interventions.
Funding
European Union’s H2020 ITN Network “MyFUN” under Marie Skłodowska-Curie (675137).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
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