The next generation spectacle lenses for myopia control

Most newer myopia control spectacle lens designs behave like a single vision lens for myopia correction, with an overlaying 'treatment zone' for myopia control.

• Clear central aperture: each has a clear single vision distance zone in the centre of the lens, usually with a diameter between 7 to 10mm.
• Alternating treatment zones: the surrounding area contains elements (e.g. lenslets) which provide myopic defocus across the retina. In the case of DOT, diffusive microdots disperse light onto the retina and modulate contrast. MPDL lenses use freeform technology (like a progressive lens) to incorporate defocus.
• Single vision ‘background’: each design (except for MPDL) has a 'background' of single vision correction throughout the periphery of the lens.
• Do not alter binocular vision or accommodation: DIMS and HAL lenses behave like a single vision lens and do not alter accommodation or binocular vision function. Early data for the DOT lens appears similar. There is no such data for the CARE or MPDL lens yet.
• Each should be fit like a single vision lens: the interpupillary distance and fitting height should be carefully measured, and the frame adjusted to securely fit the child’s face, to ensure the clear central zone is optimized for good vision and centration.

In the past, the predominant theory of myopia control was the peripheral defocus theory, whereby the peripheral retina receives myopic defocus as a slow-down or stop signal for eye growth. More recently, the prevailing thought is the simultaneous myopic retinal defocus theory. 

The simultaneous myopic defocus theory involves two planes of focus:

1. One plane on the retina to correct myopia
2. A second plane in front of the retina for myopic defocus - anywhere across the retina, and not just in the periphery

DIMS technology works on the concept of creating simultaneous defocus, during both distance and near viewing - one plane on the retina due to the single vision zone(s) of the lens, and one plane creating myopic defocus due to the +3.50D defocus lenslets.1

HAL technology takes this a step further by introducing the concept of a 'volume of myopic defocus'. Consider this a shift in theory from simultaneous defocus in two planes (one being on the retina to correct myopia, and the other in front of the retina for myopic defocus) to a three-dimensional 'volume' of defocus in front of the retina of varying dioptric power.2

CARE lenses use the myopic defocus theory, by employing cylindrical refractive elements to generate defocus. With cylindrical elements rather than traditional spherical ones, the light that passes through them doesn't focus to a single point.3 The unique shape of these cylinders, along with the surrounding clear and defocus zones, spreads the light out in a controlled way. This creates a soft, blended area of myopic defocus in front of the retina.

MPDL lenses are designed to induce simultaneous myopic retinal defocus during distance and near vision, like DIMS and HAL lenses. However, the lens uses a freeform design for producing defocus, rather than lenslets. The treatment area incorporates a peripheral defocus of +1.50 D nasally, +1.80 D temporally, and +2.00 D inferiorly.4 Based on theories that nasal and temporal regions of the retina have differing sensitivity to defocus,5 the asymmetric design was optimized to align with the shape of the myopic retina.

DOT lenses are based on the contrast theory of myopia – an entirely different approach. Instead of employing lenslets to create simultaneous defocus, the SightGlass DOT lens uses diffusers to modulate retinal contrast.6 The contrast theory hypothesizes that overstimulation of the retina from high contrast is associated with overstimulation of eye growth, thus instigating myopia progression.7

HOYA MiYOSMART spectacle lenses use Defocus Incorporated Multiple Segments (DIMS) technology, designed by Hong Kong Polytechnic University. 

DIMS spectacle lenses comprise a central optical zone (9 mm in diameter) for correcting distance refractive errors. This is surrounded by a 33 mm diameter annular zone with multiple segments, with each segment having a relative positive power of +3.50 D and diameter of 1.03 mm. This design simultaneously introduces myopic defocus and provides clear vision for the wearer at all viewing distances.1

Essilor Stellest™ spectacle lenses incorporate Highly Aspherical Lenslet (HAL) technology in their lens design.

HAL spectacle lenses are comprised of a spherical front surface with 11 concentric rings formed by contiguous aspherical lenslets (diameter of 1.1 mm). The area of the lens without lenslets provides distance correction. 

The geometry of aspherical lenslets has been calculated to generate a volume of myopic defocus (VoMD) in front of the retina at any eccentricity, serving as a myopia control signal.2 The use of highly aspherical lenslets allow rays of light to be deviated in a manner that creates a three-dimensional quantity of light in front of the retina. The use of lenslets with greater asphericity contributes to a larger VoMD, which in turn is purported to reduce lens-induced myopia in chicks.

In the two-year randomized clinical trial, Chinese children (n=157) aged 8-13 years with myopia of -0.75D to -4.75D were randomized into either single vision (SV), highly aspherical lenslet (HAL) or slightly aspherical lenslet (SAL) spectacle lenses. After two years, myopia progressed by -0.66D/0.34mm in the HAL group, -1.04D/0.51mm in the SAL group and -1.46D/0.69mm in the SV group. 

Daily wearing time was self-reported, with a mean of around 13.5 hours per day, similar across the groups. Children who self-reported wearing the HAL lenses at least 12 hours every day showed 0.99D less final myopia and only 0.28mm of total axial growth over two years.

Long-term studies have been published on HAL spectacle lenses. The 5-year data showed that children who continuously wore HAL spectacle lenses for 5 years had 1.75D less myopia progression, 0.72mm less axial elongation, and 29% reduced incidence of high myopia, compared to controls. Additionally, 6-year data has been announced, pending journal publication.

SightGlass Vision DOT spectacle lenses use Diffusion Optics Technology (DOT), which are a little bit different from DIMS and HAL in that they do not use lenslets, but diffusers. 

What are these diffusers? They are thousands of small elements across the lens, shaped as dots that scatter light onto the retina and slightly reduce contrast. The small (around 5mm) central section of the lens does not incorporate these dots, providing clear vision and facilitating lens power verification.

DOT lenses are based on the contrast theory, which suggests that high retinal contrast signals (e.g. in indoor environments) may stimulate axial elongation.6 Low retinal contrast (e.g. in outdoor environments) on the other hand, signals the eye to slow or stop growing.

SightGlass Vision DOT lenses have been investigated in the CYPRESS study, a 4-year multicenter randomized controlled trial undertaken in North American children aged 6-10 years, with myopia of -0.75 to -4.50D.9 As the study was undertaken during the COVID-19 pandemic, the outcomes were impacted by public health restrictions.

Despite the significant disruption, DOT lenses reduced axial elongation by 0.20 mm and refractive error progression by 0.52 D compared to controls over four years. The most significant treatment benefits were observed in the first year (pre-COVID) – a 0.40D (74%) reduction in myopia progression and a 0.15mm (50%) reduction in axial elongation. In the fourth year, eye growth in DOT wearers was similar to physiological eye growth observed in age-matched emmetropic eyes.

Zeiss MyoCare and MyoCare S are two variants of Cylindrical Annular Refractive Element (CARE) spectacle lenses, manufactured by ZEISS Vision Care International GmbH (Germany).

The CARE lens incorporates a 7 mm central zone, whereas the CARE S lens incorporates a 9 mm central zone. The nominal power of the cylindrical elements for CARE is +9.2 D and translates to a mean relative positive power of +4.6 D, whereas with CARE S, the nominal power of the cylindrical elements was +7.6 D and translated to a mean relative positive power of +3.8 D. 

The two lenses were originally designed as part of a one-year clinical study to determine if a higher positive power (CARE) could provide a greater myopia control efficacy (compared to CARE S).3

In a 2-year randomized controlled trial, 240 Chinese children (aged 6 to 13) with myopia -0.75D to -5.00D were randomly assigned either CARE lenses (80 children), CARE S lenses (80 children) or single-vision (SV) lenses (57 children). 

12-month results showed CARE lenses slowed myopia progression by 0.28D (43% reduction) and CARE S by 0.27D (41% reduction) compared to SV lenses.3 Axial length progression was also 0.12mm less with CARE lenses (a 37% reduction) and 0.10mm with CARE S lenses (31% reduction).

Asymmetric myopic peripheral defocus lenses (MPDL, IOT MyoLess) utilize a freeform design to induce simultaneous myopic retinal defocus for both distance and near vision.

MPDL lenses feature a 7 mm central ovoidal optic zone surrounded by a peripheral treatment area comprising relative positive powers of +1.50 D nasally, +1.80 D temporally, and +2.00 D inferiorly. As a result of the distribution of progressive power across the area of the lens, MPDL lenses produce asymmetrical myopic defocus along the horizontal direction.4 

The asymmetrical power progression between the nasal and temporal areas of the lens was designed to optimize the lens’ myopia control effects. Faria-Ribeiro et al. reported that a nasal-temporal asymmetry at the retina may be associated a slower progression of myopia.10 In eyes with progressive myopia, the nasal-temporal asymmetry was not observed. MPDL lenses incorporate an asymmetric power profile to replicate retinal asymmetry and harness its purported inhibitory effects on myopia.

In a 1-year randomized controlled trial conducted in Spain, children aged 6-12 years (n=69) with myopia less than −0.50 D were randomly assigned to wear either MPDL or SVL. 12-month results showed that MPDL lenses slowed myopia progression by 0.25D, and axial elongation by 0.09 mm (39%), compared with SV lenses.

2-year results have recently been published for the same trial, finding that MPDL lenses reduced myopia progression by 0.23D (53%) and axial elongation by 0.10 mm (29%) compared with SV lenses.5

As direct comparisons cannot be made between studies, we cannot definitively say which of these treatments is clearly superior.

However – based on their one-year randomized controlled trial results, DIMS (HOYA MiYOSMART), HAL (Essilor Stellest), and DOT (SightGlass DOT) lenses appear to have similar efficacy. These interventions can all be described as "slowing progression by at least half".

Below is an overview of the 6- and 12-month results for each of the lens designs.

^#Available in Canada and UK – not yet available in Australia. 

*Zeiss MyoCare also has a ‘CARE S’ design - there were no significant differences between this and the CARE results in overall efficacy.

**NA = not available (data not specified)

What do you see in those results? Let's compare the changes between the control and treatment groups. Keep in mind that we can't directly compare percentage efficacy across multiple studies.

1. Control groups. The single vision wearers in each study had similar axial length progression at 6 and 12 months, albeit perhaps slightly slower for the DOT lens control group, for which 6 month data was not available. This is interesting as the DOT lens study includes a younger population, but was undertaken on an ethnically diverse population across 14 sites in North America, compared to the other three studies undertaken on children in China. Refractive progression in the control group was more variable, as this is a less precise measure.
2. Treatment groups. Similar axial length progression at 12 months appears in the DIMS, HAL and DOT lens data. Without direct comparison it cannot be concluded with certainty, but the CARE study progression the treatment group does look to be greater than in the other three studies. When it comes to refractive progression, the story appears to be similar.