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Ophthalmology
Different kinds of therapies (optical, pharmaceutical, environmental, or behavioral) have been researched to prevent or postpone the beginning of myopia and to decrease its progression in order to minimize the associated ocular diseases connected to myopia. Regarding environmental approaches, several meta-analyses have shown that spending more time outside is associated with a lower incidence of myopia.
- myopia
- myopia control
- myopic defocus
- spectacle lens
- defocus incorporated multiple segments
1. Pharmacological Treatment
Pharmacological treatment with low-dose 0.01% atropine has been shown to be the most effective strategy for decreasing myopic development in different studies, with successful rates varying from 45 to 77% regarding refractive error reduction, but no impact on axial length [4,18,21]. Although functionally successful, this approach displayed long-term adverse effects including photophobia, glare, and accommodation loss [18,22,23].
2. Ortho-Keratology
The research for alternatives has led to an increase in orthokeratology, or ortho-K (OK), which exploits specially designed and fitted contact lenses to temporarily reshape the cornea [24]. Orthokeratology has shown beneficial effects against myopia progression and axial elongation by 30 to 55 percent [25,26]. The most common complication of ortho-K treatment was corneal staining, with other clinically significant side effects including epithelial iron deposit, prominent fibrillary lines, and transient changes of corneal biomechanical properties, but no long-term effects on the corneal endothelium were observed [27]. In contrast, those contact lenses needed careful maintenance for eye health, because improper handling or cleaning increases the risk of infection, although the risk of microbial keratitis reported in a systematic review was found to be similar to other overnight corneal reshaping lenses [28,29].
3. Contact Lenses
Over time, bifocal (BFSCL) or multifocal soft contact lenses (MFSCL), peripheral gradient lenses, extended depth of focus (EDOF) contact lenses, and progressive addition lenses have all been explored to manage myopic development [16,30,31,32,33,34,35,36,37]. The first generation of bifocal or dual-focus lenses used a concentric zone of rings with plus power addition, resulting in a peripheral myopic defocus. These designs adopted a gradual increase in the positive power toward the periphery (progressive design) or featured discrete zones (concentric ring design), with the peripheral area of the lens having a considerably higher positive power. Concentric ring designs allow stronger axial elongation control than progressive ring designs, but refraction alterations are comparable [4]. Globally, these bifocal soft contact lenses reported a 30–38% reduction in myopia development regarding refraction, and a 31–51% reduction in axial length [38]. Moreover, other research studies have reported that the efficacy of bifocal contact lenses may improve in particular settings: increased usage time, high-rate myopic progression, structural designs with a greater hyperopic power in the mid-periphery [31]. MiSight is an example of a multizone design contact lens which has demonstrated decreased myopia progression (59%) and axial development of the eye (52%) during a three-year follow up [16,30].
Among these approaches, To Chi-ho and Carly Lam from the Centre for Myopia Research under PolyU’s School of Optometry have developed Defocus Incorporated Soft Contact (DISC) lenses [33], which consist of a central correction zone and a series of alternating defocusing and correction zones spreading to the perimeter in a 50:50 ratio, with the defocusing zones at +2.5 D, whereas the corrective zones match the distance prescription. As a result, the daily wearing of DISC lenses significantly slowed axial elongation and myopia progression by 25% when compared to controls [33]. A recent update in the contact lens approach for myopia control was reported by Walline et al. who conducted the BLINK clinical trial, in which children wearing high add power (+2.50 D) MFSCL had significantly less myopia progression and axial elongation over three years, when compared to SV lenses [39].
Similar to ortho-K, the contact lenses approach carries several management problems, linked with infections, corneal traumatism, and long-term biocompatibility.
4. Spectacle Lenses
In comparison to contact lenses and pharmaceutical therapies, intervention with spectacle lenses is a straightforward and less intrusive way for children and their parents, particularly for children under the age of eight [12]. The best prescription must be validated according to associated risk factors, taking into account several patient-specific characteristics connected to myopia development and progression [5]. Single-vision (SV) spectacle lenses have been found to provide less than a 14% decrease in myopia progression. In contrast to SV spectacle lenses, multiple articles have suggested that myopic defocus (MD) slows eye development and progression, whereas hyperopic defocus enhances eye growth [40,41,42]. Nevertheless, differently from previously thought, a recent systematic review reported that under-correction of myopia is not recommended as it did not slow myopia progression [43].
Many investigations have analyzed several kinds of new spectacle lens with relative peripheral defocus, with conflicting initial results [32,44]. Bifocals or progressive additional lenses (PALs) were introduced, allowing the user to see well at distances and up close, reducing accommodative strain and lag during prolonged near work [45]. In many investigations, these lenses showed therapeutic improvements ranging from 6% to 50% as compared to SV spectacles. A stronger impact was found in children with a higher degree of myopia (>3.0 D), accommodative lag, or near esophoria [45,46]. However, in comparison to single vision lenses (SVLs), bifocal spectacles or PALs had little impact in delaying myopia development during meta-analysis, with moderate-certainty evidence. Furthermore, the same meta-analysis highlighted that previously designed peripheral defocus-correcting lenses had mixed results in terms of refractive error and axial length, offering a low level of evidence regarding clinical results [47,48,49].
Since April 2021, a new variety of spectacle lenses with peripheral defocusing capability, known as Defocus Incorporated Multiple Segments (DIMS) technology, have been marketed from Hoya in Germany, Austria, and Switzerland under the trade name “MiYOSMART” (Hoya Lens Thailand Ltd., Bangkok, Thailand) [50]. This dual-focus spectacle lens, similarly to DISC contact lens, has a zonal structure with tiny, circular (≈1 mm diameter) lenslets in the mid-periphery, each with add power (+3.50 D). The novelty of this technology relies on the fact that images from each lenslet do not converge to generate a single image in the focal plane corresponding to the add power, but rather numerous distinct images. DIMS lenses have been reported to substantially delay myopia development when compared to single vision (SV) lenses in a recent clinical trial, while showing an absence of the negative effects of pharmaceutical therapies and a reduction in maintenance level when compared to contact lenses [50]. Several issues, however, remain to be investigated, including the quality of vision, which refers to the comfort and frequency of visual symptoms after wearing added-power spectral lenses and the efficacy of myopia control in long-term follow-ups [51].
This entry is adapted from the peer-reviewed paper 10.3390/vision6020020
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