In recent years, the research progress on the mechanisms of myopia prevention and control has provided new insights for the design of novel spectacles. At the same time, novel spectacles have become one of the main solutions for clinical myopia management globally. Additionally, the recent breakthrough device designation given by the FDA to SightGlass Vision means that America may soon have its first commercially available set of myopia spectacles.

Despite their widespread use in Asia, there is no clinical guideline on their use, and few lenses of these designs have undergone clinical testing (see sidebar “Clinical testing on myopia control spectacles”). While research into the clinical application of myopia spectacles is still ongoing, their popularity is growing. In the article below, we will review their design and proposed mechanisms.

Spectacle features and proposed mechanisms

The designs of the spectacles discussed below vary primarily in the following features:

• Number, size, and shape (round or hexagon) of the lenslets.
• Constant or varying power, axis, and aberration of each lenslets, either by eccentricity or clockwise location.
• Arrangement of the lenslets (isolated vs. adjacent).
• Surface ratio between the distance carrier and total area of the lenslets.

The proposed mechanisms of these spectacles are as follows:

• Reducing hyperopic defocus by reducing accommodative lag. Research suggests that a greater lag of accommodation is linked to the progression of myopia, although establishing a clear causal relationship between cause and effect is not fully determined. If we assume that the occurrence of accommodative lag, a subtype of hyperopic defocus, serves as a significant stimulus for the initiation of myopia, then optical designs capable of effectively minimizing this lag could serve as a protective measure against the development and progression of myopia. Interventions, such as bifocals and progressive addition lenses (PALs), aimed at reducing accommodative demand and, consequently, diminishing accommodative lag, have been explored for myopia control for several decades.^2-5
• Reducing peripheral defocus. The concept of relative peripheral retinal hyperopic defocus has been proposed as another significant factor contributing to the development of myopia.^6-8 Studies using primate models⁹ indicate that the peripheral retina, even in the absence of visual cues from the central retina due to laser ablation of the macula, can regulate emmetropization by accurately interpreting defocus signals. Moreover, the imposition of hyperopic defocus on the peripheral retinal field can lead to accelerated axial growth and the development of myopia, even with unimpeded central vision. Double-blind randomized clinical trials grounded in this theory have demonstrated effectiveness in controlling myopia.
• Inducing higher-order aberration (HOA). The effectiveness of orthokeratology lenses in myopia control has been consistently demonstrated in numerous studies, although the precise mechanism remains unclear. A widely accepted theory proposes that the myopia-controlling effect of orthokeratology is linked to a notable increase in HOAs resulting from the treatment, especially positive spherical aberration and coma. Recent advancements in spectacles incorporating lenslets to deliberately induce HOAs have demonstrated effectiveness in myopia control.^10-12
• Reducing retinal image contrast. Studies indicate that certain lenses known for their myopia control effects can result in a decrease in retinal imaging contrast. As a result, lenses specifically crafted to reduce retinal imaging contrast have undergone clinical trials, showing promising effectiveness in myopia control.^13-15
• Dampening retinal detection of “myopia-go” signals. Despite the various theories underlying each innovative spectacle design aimed at myopia control, there is no overarching theory capable of explaining the axial-inhibiting effect of different designs that target increasing central plus power, reducing peripheral hyperopic defocus, inducing higher-order aberrations (HOAs), or decreasing retinal image contrast. One hypothesis, based on my understanding of animal studies, that is cohesive for all commercially available anti-myopia designs, is related to how the retina decodes the "myopia-go" signals, taking into account image quality, the sign and magnitude of defocus, as well as aberration signals. Unlike a camera, which records absolute values at each pixel on the screen, the retina has evolved to excel in decoding changes in both spatial and temporal domains, whether they involve color, luminance, defocus, or aberration. Essentially, all novel optical interventions for myopia control may work by reducing the retina's sensitivity in decoding the "myopia-go" signals, thereby inhibiting abnormal axial elongation.

Benefits of new technology

It's important to note that the future of these spectacles will depend on ongoing research findings, technological innovations, and the collaboration between clinicians, researchers, and industry partners. As more is learned about the underlying mechanisms of myopia, novel spectacles with lenslet technology will likely serve as the first line treatment in comprehensive myopia management in pediatric population, considering their combined advantages including convenience, safety, easiness of fitting, and relatively lower cost. OM

References

1. Expert Consensus on the Application of Spectacle Related to Myopia Prevention and Control in Myopia Management (2023). Chinese J of optometry & vision science. 2023,25(11):801-808. DOI:10.3760/cma.j.cn115909-20230920-00082
2. Hasebe S, Ohtsuki H, Nonaka T, et al. Effect of progressive addition lenses on myopia progression in Japanese children: a prospective, randomized, double-masked, crossover trial. Invest Ophthalmol Vis Sci. 2008;49(7):2781-2789. DOI: 10.1167/iovs.07-0385.
3. Edwards MH, Li RW, Lam CS, et al. The Hong Kong progressive lens myopia control study: study design and main findings. Invest Ophthalmol Vis Sci. 2002;43(9):2852-2858. DOI: 10.1007/s00417-002-0529-0.
4. Shih YF, Hsiao CK, Chen CJ, et al. An intervention trial on efficacy of atropine and multi-focal glasses in controlling myopic progression. Acta Ophthalmol Scand. 2001;79(3): 233-236. DOI: 10.1034/j.1600-0420.2001.790304.x.
5. Gwiazda J, Hyman L, Hussein M, et al. A randomized clinical trial of progressive addition lenses versus single vision lenses on the progression of myopia in children. Invest Ophthalmol Vis Sci. 2003;44(4):1492-1500. DOI: 10.1167/iovs.02-0816.
6. Benavente-Pérez A, Nour A, Troilo D. Axial eye growth and refractive error development can be modified by exposing the peripheral retina to relative myopic or hyperopic defocus. Invest Ophthalmol Vis Sci. 2014;55(10): 6765-6773. DOI: 10.1167/iovs.14-14524.
7. Mutti DO, Hayes JR, Mitchell GL, et al. Refractive error, axial length, and relative peripheral refractive error before and after the onset of myopia. Invest Ophthalmol Vis Sci. 2007;48(6):2510-2519. DOI: 10.1167/iovs.06-0562.
8. Mak CY, Yam JC, Chen LJ, et al. Epidemiology of myopia and prevention of myopia progression in children in East Asia: a review. Hong Kong Med J. 2018;24(6): 602-609. DOI: 10.12809/hkmj187513.
9. Huang J, Hung LF, Smith EL. Effects of foveal ablation on the pattern of peripheral refractive errors in normal and formdeprived infant rhesus monkeys (Macaca mulatta). Invest Ophthalmol Vis Sci. 2011;52(9):6428-6434. DOI: 10.1167/iovs.10-6757.
10. Philip K, Sankaridurg P, Holden B, et al. Influence of higher order aberrations and retinal image quality in myopisation of emmetropic eyes. Vision Res. 2014;105: 233-243. DOI: 10.1016/j.visres.2014.10.003.
11. Hiraoka T, Kotsuka J, Kakita T, et al. Relationship between higher-order wavefront aberrations and natural progression of myopia in schoolchildren. Sci Rep. 2017;7(1):7876. DOI:10.1038/s41598-017-08177-6.
12. Lau JK, Vincent SJ, Collins MJ, et al. Ocular higher-order aberrations and axial eye growth in young Hong Kong children. Sci Rep. 2018;8(1):6726. DOI: 10.1038/s41598-018-24906-x.
13. Gao Y, Lim EW, Yang A, et al. The impact of spectacle lenses for myopia control on visual functions. Ophthalmic Physiol Opt, 2021;41(6):1320-1331. DOI: 10.1111/opo.12878.
14. Chang CF, Cheng HC. Effect of orthokeratology lens on contrast sensitivity function and high-order aberrations in children and adults. Eye Contact Lens. 2020;46(6):375-380. DOI: 10.1097/ICL.0000000000000667.
15. Nti AN, Gregory HR, Ritchey ER, et al. Contrast sensitivity with center-distance multifocal soft contact lenses. Optom Vis Sci. 2022;99(4):342-349. DOI: 10.1097/OPX.0000000000001874.