Multifocal correction also caused a hyperopic shift in peripheral refraction at all locations in low myopes as demonstrated in Fig. 2A. The relative peripheral refraction profile was similar between no correction and SV and MF corrections in the temporal VF (Fig. 2B). However, there was significant myopic shift in relative peripheral refraction in the nasal VF (FN10 = 9.217, p = 0.008; FN20 = 29.491, p < 0.001; FN30 = 45.328, p < 0.001; FN35 = 18.799, p = 0.001) with MF compared with SV correction (Fig. 2B). Multifocal correction also caused a hyperopic shift in peripheral refraction at all locations in moderate myopes (Fig. 3A). Moreover, overall differences in relative peripheral refraction profile between full SV and MF correction were found (F = 16.880, p < 0.001), which were confirmed by post hoc tests specifically at 35 degrees in the temporal VF (FT35 = 8.039, p = 0.012) and all locations in the nasal VF (FN10 = 0.909, p = 0.003; FN20 = 54.100, p < 0.001; FN30 = 71.018, p < 0.001; FN35 = 50.385, p < 0.001) as illustrated in Fig. 3B.
Similarly, compared with no correction, SV and MF correction caused a significant change in the J 180 profile (F = 2.720, p = 0.003) in moderate myopes as shown in Fig. 4B. Single-vision SCL correction caused a positive increase in J 180 at 30 degrees (p = 0.004) in the temporal VF and at 30 (p = 0.018) and 35 degrees (p = 0.003) in the nasal VF, as indicated by post hoc t tests. Furthermore, compared with no correction, MF SCLs caused a negative increase at 10 (p = 0.023) and 30 degrees (p = 0.021) in the nasal VF. In addition, compared with SV correction, MF correction caused a negative shift in J 180 at 10 (p = 0.012), 20 (p = 0.014), 30 (p = 0.001), and 35 degrees (p = 0.001) in the nasal VF in moderate myopes.
Experimental animal studies investigating vision-dependent mechanisms that regulate refractive error development have demonstrated that, contrary to traditional belief, refractive error development seems to be influenced more by peripheral defocus than previously believed.27,28 Recently, Smith et al.26 imposed hyperopic peripheral defocus with unrestricted central vision in infant rhesus monkeys with intact and photoablated foveas. Imposing this hyperopic defocus in the periphery was found to promote the development of central axial myopia in the presence of both functioning and nonfunctional foveas. Liu and Wildsoet29 demonstrated in the chick eye model that a plano center and +5 D periphery concentric bifocal spectacle lens tended to produce central hyperopia coupled with apparent inhibition of axial length elongation. More recently, Ho et al.46 demonstrated differences in human retinal electrical response to defocus with the paracentral retina responding more strongly to defocus compared with the central retina, further supporting the theory that refractive error development is more influenced by peripheral visual signals. Consequently, it has been hypothesized that inducing a myopic defocus onto the peripheral retina of progressive myopes might potentially slow or stop the progression of central myopia.36 Therefore, optical means of manipulating peripheral vision have become of great interest and may provide a possible strategy for myopia control in humans.
Antimyopia MF SCLs with plus power in the periphery to induce myopic defocus onto the peripheral retina have been developed as a means of myopia control. However, there are commercially available MF SCLs, traditionally fitted for presbyopic correction, which have similar designs to these novel antimyopia SCLs. The purpose of this study was to determine the effects of Proclear Multifocals (Coopervision), a commercially available SCL that has a distance center correction and a plus add (+2.00 DS) periphery design, on peripheral refraction in young adult myopes compared with SV SCLs.
Myopic shifts in relative peripheral refraction profiles were found in both low and moderate myopes wearing MF compared with SV SCLs. Although an absolute myopic defocus was apparent at most eccentric locations in both low and moderate myopes, a full +2.00 D myopic shift in peripheral refraction was not measured. This is likely to be caused by the autorefractor averaging refraction across its 2.3-mm measurement ring rather than measuring refraction at a single defined point on the retina. The myopic shift was more apparent in the nasal compared with the temporal VF, and this is likely to be caused by temporal decentration of SCLs, an effect which has been previously noted.40,47 As animal studies have suggested that the effects of optical defocus on refractive error seem to be locally mediated,25 this asymmetric refractive shift induced by MF SCLs must be viewed with caution. Corresponding regional changes in ocular shape have been demonstrated with optical defocus induced over restricted retinal regions in primates,48,49 and thus, there is a possibility that MF SCLs may promote undesirable asymmetric ocular growth in human myopes. Future longitudinal studies on the effects of MF SCLs on ocular shape are indicated. Furthermore, eyes that demonstrate poor SCL centration may not be suitable to wear MF SCLs as a potential form of myopia control.
As previously mentioned, Proclear Multifocal SCLs used in this study are of similar design to MF SCLs that have been specifically developed for potential myopia control. The AMCL is a silicone hydrogel SCL designed to induce myopia on to the peripheral retina. The design of this contact lens is described in detail elsewhere.40 Axial length increase after 12 months of AMCL wear in 43 children of Chinese ethnicity was 0.27 mm (95% confidence interval, 0.22 to 0.32 mm) and 0.40 mm for 39 spectacle lens wearers (95% confidence interval, 0.35 to 0.45 mm), equivalent to approximately 33% less myopia progression in the AMCL group. Compared with spectacle lens wearers, myopic shift in relative peripheral refraction was found in children wearing these novel SCLs at 20, 30, and 40 degrees in the nasal VF and at 30 and 40 degrees in the temporal VF.40 A more myopic relative peripheral refractive profile was found with the AMCL compared with baseline.
The Dual-Focus lens, commercially known as the MiSight lens (Coopervision), was developed and investigated by Anstice and Phillips39 who similarly demonstrated reduced myopia progression with these MF SCLs in a group of 40 myopic children aged between 11 and 14 years. Subjects were randomized to wear the Dual-Focus lens in one eye and an SV SCL in the contralateral eye for 10 months (period 1). Lens assignment was then swapped for the second 10 months (period 2). During period 1, axial length elongation of 0.11 ± 0.09 mm compared with 0.22 ± 0.09 mm was measured in the eyes wearing the Dual-Focus lens and SV SCL, respectively. After the crossover period, the eye now wearing the Dual-Focus lens was reported to show axial elongation of 0.03 ± 0.10 mm compared with the eye now wearing SV SCLs, which had axial elongation of 0.14 ± 0.09 mm. We are unaware of any published reports on peripheral refraction changes with the Dual-Focus lens.
Although the described antimyopia MF SCLs have been developed based on the hypothesis that peripheral hyperopia, present in a typical myope, may stimulate central myopia development, there have been studies contradicting this hypothesis. Sng et al.54 found that the development of myopia was associated with a change in peripheral refraction from relative myopia to relative hyperopia, indicating that peripheral refraction may be more a reflection of ocular shape change rather than being a myopiogenic factor. Furthermore, analysis of results from the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) study found no significant association between the amount of relative peripheral hyperopia and risk of onset of central myopia.55 However, it must be noted that peripheral refraction was measured in only one position (30-degree temporal gaze) in the entire VF. Very recently, Jaeken and Artal56 measured peripheral optical quality using a Hartmann-Shack wavefront sensor. Peripheral defocus and oblique astigmatism were found to be the main contributors to degradation of the peripheral image in both emmetropic and myopic eyes. Furthermore, they found the amount of peripheral blur to be similar between the two refractive groups and therefore argued against the hypothesis of retinal defocus influencing refractive error development. They proposed that if emmetropization is driven by peripheral blur, differences in peripheral blur would be expected between emmetropic and myopic eyes. However, this was not the case.
Despite conflicting reports and new perspectives on the theory of myopia control through manipulation of peripheral defocus, studies have shown that optical methods that reduce the amount of hyperopia induced onto the peripheral retina, in particular the antimyopia MF SCLs,39,40 seem to slow down the progression of myopia. In this study, refraction measured with the Proclear MF SCLs with center distance correction and +2.00 D add periphery was myopic at most locations along the horizontal VF meridian. According to the peripheral defocus hypothesis, this peripheral myopia may be antimyopiogenic. For clinicians who do not have access to the MiSight or Dual-Focus lenses, the results from this study suggest that the Proclear MF SCL can be used as an alternative for potential myopia control in progressive myopic children, although caution must be taken as induced peripheral refraction profiles with MF SCLs were found to be asymmetric in this study. Thus, myopic children with poor lens centration may not be suitable for myopia control with MF SCLs. However, studies of the long-term efficacy of MF SCL wear for myopia control in children are lacking, and further research is indicated.
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