Optimizing Multifocal Management of Myopia

Scott Read

Soft multifocal contact lenses, which simultaneously focus light from both distant and near objects, have been increasingly used for the correction of presbyopic patients in the past 2-3 decades. More recently, new applications have emerged for these lenses in the area of myopia control. We now have substantial evidence that soft multifocal lenses can significantly slow progression in myopic children. Studies of a range of different multifocal lens designs across different populations show that soft multifocal contact lenses can slow myopic eye growth, typically by between 30-60%. [1] From an optical point of view, soft multifocal contact lenses that have a central distance zone and a more peripheral near zone introduce increased levels of spherical aberration that result in greater positive refractive power (resulting in myopic defocus) in the marginal pupil region.[2]

While soft multifocal lenses have been shown to influence accommodative posture and binocular vision characteristics,[3] the most likely mechanism underlying the effects of these lenses on eye growth and myopia progression is the impact of this positive refractive power (myopic defocus, in which light is focused in front of the retina) that is introduced by soft multifocal lenses. Myopic defocus is well documented to slow eye growth in animal studies, and there is mounting evidence of the same outcome in human eyes.[4]

Figure 1: The optical effects of multifocal lenses, illustrating the natural bare eye higher-order wavefront aberrations of a myopic subject (left) and the altered higher-order aberration profile associated with multifocal soft contact lens wear in this subject (right). Images courtesy of Dr. Rohan Hughes.

The recent publication of the outcomes from the BLINK study [5] provides further evidence supporting the safety and efficacy of multifocal contact lenses in childhood myopia control. This study examined medium and high addition power multifocal lenses and found significantly greater reductions in axial eye growth in the high add group. This evidence of an apparent dose-response effect associated with the optical properties of the lenses from this study suggests the promising possibility that further improvements in myopia control efficacy may be possible, with optimised optical designs that introduce higher levels of myopic defocus.

To optimise multifocal contact lenses for myopia control, there are multiple considerations. Regarding treatment effects, it is important to note that the quoted slow-down in myopia progression from clinical trials is typically a mean for the population studied, with some children showing much better response and some worse response/efficacy than this mean treatment effect. Understanding the reasons underlying these variations in response will be important for optimising treatments in the future.

The optical effects of the lenses will interact with the natural aberrations and pupil size of children’s eyes (Figure 1). Therefore, an improved understanding of the optics of myopic children’s eyes – and how this interacts with treatment effects – may assist in the design of novel approaches for increased efficacy. The eye’s aberrations also change during accommodation (with an increase in negative spherical aberration typically noted) therefore, understanding how the optics of myopic children’s eyes change during accommodation and how this interacts with the optical effects of lenses and their treatment effects is another important area.

While improvements in treatment effects may be possible by altering the magnitude and distribution of the optical power of the lenses, it may be the case that a ‘one-size fits all’ approach would not be sufficient for optimal treatment of all children, and a customised approach to optimise the lens optical effects may be required. Given the visual demands of the modern child,[6] and the importance of clear vision for educational achievement, it is also critical that the visual function impact of myopia control lenses is considered to ensure that multifocal lenses don’t negatively impact children’s visual function.

While it is clear that significant work is needed in multiple areas to better understand the optical effects of multifocal lenses and how they can optimally impact childhood eye growth to achieve improved myopia control outcomes, results to date suggest that clinically significant effects can be achieved with current lens designs, with the promise of improved outcomes in the future as our understanding of the optical effects on eye growth continues to improve.

References

1. Wildsoet CF, Chia AWL, Cho P, Guggenheim JA, Roelof-Polling J, Read SA, Sankaridurg P, Saw S-M, Trier K, Walline JJ, Wu P-C, Wolffsohn JS. IMI – Interventions for myopia onset and progression report. Invest Ophthalmol Vis Sci. 2019 60: M106–M131018.
   
2. Bakaraju RC, Ehrmann K, Ho A et al. Inherent ocular spherical aberration and multifocal contact lens optical performance. Optom Vis Sci. 2010 84: 1009-1022.
   
3. Gong CR, Troilo D, Richdale K. Accommodation and phoria in children wearing multifocal contact lenses. Optom Vis Sci. 2017 94: 353–360.
   
4. Chakraborty R, Ostrin L, Benavente-Perez A, Verkicharla PK. Optical mechanisms regulating emetropisation and refractive errors: evidence from animal models. Clin Exp Optom. 2020 103:55-67.
   
5. Walline JJ, Walker MK, Mutti DO et al. Effect of high add power, medium add power, or single vision contact lenses on myopia progression in children. The BLINK randomized clinical trial. JAMA. 2020 324:571-580.
   
6. Narayanasamy S, Vincent SJ, Sampson GP, Wood JM. Visual demands in modern Australian primary school classrooms. Clin Exp Optom. 2016 99:233-40