Spectacle options for myopia control are a highly appealing prospect to commence early intervention for children who are younger or less willing to wear contact lenses.
Two new designs – Defocus Incorporated Multiple Segments (DIMS) and Highly Aspherical Lenslet Target or H.A.L.T. technology – have been researched and developed. DIMS has been licensed to Hoya and is now available in Australia. H.A.L.T. has been developed by Essilor and is eagerly anticipated by the local market.
Here Dr Paul Gifford investigates these two designs, their presumed mechanism and comparative efficacy for myopia control, based on published research.
The newest myopia controlling spectacles can correct and control myopia as well as the most effective contact lens options. Additionally, they are more effective in slowing childhood myopia progression than bifocal or progressive addition spectacle lenses.1
when the child looks away from the clear central zone, they receive simultaneous in-focus information from the single vision distance correction… and myopic defocus information
The technology underpinning these new myopia controlling spectacles – H.A.L.T. and DIMS – can be pictured, in general terms, as a single vision lens for myopia correction with a superimposed array of tiny lenslets across the surface. For clear central vision, there is a window in the middle of the lens where no lenslets exist. Spaces between the lenslets provide single vision distance correction in oblique viewing positions. The difference between the two lens designs comes down to the array, volume and optical power of the lenslets in each.
This new technology asks us to think differently about how a spectacle lens works.
WHAT IS DIMS AND H.A.L.T. TECHNOLOGY?
Both DIMS and H.A.L.T. technology spectacle lenses take a step beyond the traditional spectacle to behave more like a myopia controlling contact lens. The benefit of a contact lens is that it moves with the eye, so the same optical profile is provided to the central and peripheral retina, regardless of the angle of view. This is easy to imagine in the case of a soft multifocal or dual-focus myopia controlling contact lens, worn on the eye during the day. In the case of orthokeratology, the treatment is ‘fixed’ through the overnight corneal profile change.
Think of DIMS and H.A.L.T. technology as like a single vision lens for myopia correction, with an overlaying ‘treatment zone’ for myopia control.
- Each has a clear single vision distance zone in the centre of the lens, and a ‘background’ of single vision correction in the periphery of the lens,
- Each has a surrounding zone of lenslets to create a differential myopic defocus across the retina, with spaces in between them for the single vision correction,
- Each behaves like a single vision lens in that they do not alter accommodation or binocular vision function as do progressive addition and bifocal spectacle lenses, and
- Each should be fit like a single vision lens, with careful attention paid to measuring the fitting height to ensure the child makes the most of the clear central zone for best acuity.
While an eye moves behind a spectacle lens, these new lenses can be thought of as ‘behaving more like a myopia controlling contact lens’ because, when the child looks away from the clear central zone, they receive simultaneous in-focus information from the single vision distance correction (falling on the retinal plane) and myopic defocus information (falling somewhere in front of the retinal plane). This is likely why their myopia control efficacy seems to exceed any of the previous spectacle lens solutions and equals that of dual focus soft and orthokeratology contact lenses,1 with a similar mechanism of action to the contact lens options.
PRESUMED MECHANISM OF ACTION
The long-standing theory of myopia control mechanisms is that of peripheral defocus, whereby the peripheral retina receives myopic defocus as a slow-down or stop signal for eye growth.2 The more recent thought has evolved to the simultaneous myopic retinal defocus theory. This can be pictured as two planes of focus; one being on the retina to correct myopia, and the other in front of the retina for myopic defocus, which could be anywhere across the retina and not just in the ‘periphery’. The latest research on this in animal models has sought to understand where on the retina (e.g. how far into the periphery) and how much defocus difference is required.3
DIMS technology works on the concept of creating simultaneous defocus, during both distance and near viewing, with 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.4
H.A.L.T. technology takes this a step further by introducing the concept of a ‘volume of myopic defocus’.5 This terminology and theory, as applied to human interventions, is new to the field. However, it is cited in the clinical trial paper5 as having a basis in the use of aspherical lenses with a power gradient in animal studies. 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.
DIMS TECHNOLOGY IN MIYOSMART BY HOYA
DIMS technology was designed by Hong Kong Polytechnic University. It is described in the clinical trial paper as “compris[ing] a central optical zone (9mm in diameter) for correcting distance refractive errors, and an annular multiple focal zone with multiple segments (33mm in diameter) having a relative positive power (+3.50D). The diameter of each segment is 1.03mm. This design simultaneously introduces myopic defocus and provides clear vision for the wearer at all viewing distances. There are multiple foci from myopic defocus at a plane in front of the retina, which would be received as blur images on the retina.”4
In the two year randomised clinical trial, Hong Kong Chinese children aged eight to 13-years with myopia -1.00 to -5.00D, and no more than 1.50D astigmatism, wore either single vision distance (SV) or the DIMS spectacle lens. After two years (n=160), their average myopia progression was -0.41D vs -0.85D and 0.21mm vs 0.55mm in DIMS and SV respectively, representing around a 50% refractive and 60% axial length control effect.4 This is an absolute control effect of 0.44D and 0.34mm less myopia over two years.
The paper reported that 21.5% of children who wore DIMS had no myopia progression over two years, compared to only 7% of those who wore SV lenses. Distance and near acuity in DIMS was similar to SV at around 6/6 or 20/20. While children with strabismus or binocular vision (BV) anomalies were excluded from the study, DIMS showed no influence on near phoria or lag of accommodation compared to SV. A newly published three-year study7 also showed continued good results, as the SV wearing children were switched into DIMS.
H.A.L.T. TECHNOLOGY IN STELLEST BY ESSILOR
Essilor’s Stellest lens is described as comprising Highly Aspherical Lenslet Target (H.A.L.T.) technology.8 The recent publication of the one year clinical trial paper5 describes these spectacle lenses as having “a spherical front surface with 11 concentric rings formed by contiguous aspherical lenslets (diameter of 1.1mm). 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 in front of the retina at any eccentricity, serving as a myopia control signal (Figure 2).” The clinical trial paper5 describes the use of aspherical lenses with a power gradient in animal studies as a basis for use of the highly aspherical lenslets. It states that “Instead of focusing light on two distinct surfaces, as in the case of competing defocus lenses, these aspherical lenses deviate rays of light continuously in a nonlinear manner that creates a threedimensional quantity of light in front of the retina, which we call volume of myopic defocus (VoMD) in this paper. Greater asphericity, that is, a larger VoMD, reduces lens-induced myopia in chicks.”
The one year results of the ongoing randomised clinical trial were recently reported. Chinese children aged eight to 13-years with myopia of -0.75D to -4.75D were randomised into either single vision, highly aspherical lenslet (HAL) or slightly aspherical lenslet (SAL) spectacle lenses.
After one year, (n=161) myopia progressed -0.81D/0.36mm in SV, -0.48D/0.25mm in SAL and -0.27D/0.13mm in HAL.5 This represents around a 70% refractive and 60% axial length efficacy for HAL and 40% refractive and 30% axial length efficacy for SAL. The absolute effects were 0.54D/0.23mm less myopia for HAL wearers and 0.33D/0.11mm less myopia for SAL wearers.
Axial length was stable over the one year study in 28% of the HAL group, 9% of SAL and 0% of SV groups. Distance and near acuity was no different between the groups, being around 6/6 (20/20) at distance and 6/7.5 (20/30) at near. There was no influence of the SAL or HAL lens design on near phoria or lag of accommodation.5
A research abstract on the two-year clinical trial data9 reported that myopia progressed -1.46D/0.69mm in SV, -1.04D/0.51mm in SAL, and -0.66D/0.34mm in HAL. In children who wore their lenses every day for at least 12 hours per day, the absolute myopia control effect compared to SV was 0.99D/0.41mm less myopia in HAL and 0.57D/0.26mm less myopia in SAL.
HOW DO THEY COMPARE FOR EFFICACY?
Currently, we have a one year randomised controlled trial for H.A.L.T. technology5 and two years for DIMS,4 both published as full scientific papers. Two year peerreviewed data is available for H.A.L.T., but not yet as a full paper.9 Both have been conducted with Chinese children aged eight to 13-years as participants, and with similar baseline characteristics. In both studies, a single vision distance (SV) spectacle lens was worn by the control group. Since the highly aspherical lenslets (HAL) group had the larger myopia control effect in the newer study,5 this data will be compared to DIMS after 12 months for each lens type.
It is also important to compare the control groups for each study to understand any differences contributing to the absolute and percentage effects observed. When comparing the treatment and control groups for each study, we need to keep in mind that direct statistical comparison isn’t possible – instead viewing the means and standard deviations for similarity is the best approach.
In absolute terms, the children in the HAL study – both treatment and control groups – had slightly more refractive progression than the children in the DIMS study, but their axial length progression was similar to the DIMS study participants.4,5 Given that axial length measurement by interferometry techniques is around seven times more accurate than cycloplegic refraction,10 these are the more relevant results.
In relative terms, the percentages are similar. For axial length, DIMS controlled growth by 66% and HAL by 64% over 12 months. As recent analysis has explained, percentages must be carefully applied only to the duration of the study and not extrapolated further, as percentage treatment effect changes over time and tends to be greatest in the first 12 months.1
Both lenses provide a valuable innovation for myopia control in children, with comparative efficacy to dual-focus soft contact lenses, orthokeratology and 0.05% atropine.1 It’s important to start an intervention for myopia control as soon as possible, to have the greatest impact in reducing final myopia,1 and such effective spectacle lens options open the door to myopia management for younger children, those not ready for contact lenses, and even for prescribing as a powerful back-up or part-time option with myopia controlling contact lens wear.
Dr Paul Gifford is a research scientist and industry innovator who graduated as an optometrist from City University, London in 1995, then worked in clinical practice for a decade before being awarded his PhD in hyperopic orthokeratology and contact lens optics in 2009 from the University of New South Wales (UNSW), Sydney. Dr Gifford’s experience includes every facet of the optometry profession, from clinical practice to academia, research and industry. He holds over 60 peer reviewed and professional publications, and has presented more than 70 conference lectures in Australia and internationally. Dr Gifford holds three professional fellowships; and has been conferred two prestigious research awards from the British Contact Lens Association, along with seven other research awards during his PhD, and two post-doctorate research grants. He holds an adjunct academic position at UNSW and consults to the contact lens industry on projects relating to product and systems design and software solutions including machine learning. He is a co-founder and director of the education platform Myopia Profile.
- Brennan NA, Toubouti YM, Cheng X, Bullimore MA. Efficacy in myopia control. Prog Retin Eye Res. 2020 Nov 27:100923.
- Smith EL 3rd. Prentice Award Lecture 2010: A case for peripheral optical treatment strategies for myopia. Optom Vis Sci. 2011 Sep;88(9):1029-44. doi: 10.1097/ OPX.0b013e3182279cfa. PMID: 21747306; PMCID: PMC3371664.
- Smith Iii EL, Arumugam B, Hung LF, She Z, Beach K, Sankaridurg P. Eccentricity-dependent effects of simultaneous competing defocus on emmetropization in infant rhesus monkeys. Vision Res. 2020 Dec;177:32-40.
- Lam CSY, Tang WC, Tse DY, Lee RPK, Chun RKM, Hasegawa K, Qi H, Hatanaka T, To CH. Defocus Incorporated Multiple Segments (DIMS) spectacle lenses slow myopia progression: a 2-year randomised clinical trial. Br J Ophthalmol. 2020 Mar;104(3):363-368.
- Bao J, Yang A, Huang Y, Li X, Pan Y, Ding C, Lim EW, Zheng J, Spiegel DP, Drobe B, Lu F, Chen H. One-year myopia control efficacy of spectacle lenses with aspherical lenslets. Br J Ophthalmol. 2021:318367.
- Lam CSY, Tang WC, Tse DY, Lee RPK, Chun RKM, Hasegawa K, Qi H, Hatanaka T, To CH.Defocus Incorporated Multiple Segments (DIMS) spectacle lenses slow myopia progression: a 2-year randomised clinical trial. Br J Ophthalmol 2020;104:363–368. doi:10.1136/ bjophthalmol-2018-313739.
- Lam CS, Tang WC, Lee PH, Zhang HY, Qi H, Hasegawa K, To CH. Myopia control effect of defocus incorporated multiple segments (DIMS) spectacle lens in Chinese children: results of a 3-year follow-up study. Br J Ophthalmol. 2021 Mar 17:bjophthalmol-2020-317664.
- Press Release: www.essilor.com/en/medias/pressreleases/ essilors-game-changing-stellest-lens-shownto- slow-down-myopia-progression-in-children-by-morethan- 60-after-one-year-interim-clinical-trial/. Accessed 5th October 2021.
- Bao J, Huang Y, Li X, Yang A, Lim EW, Spiegel D, Drobe B, Chen H. Myopia control with spectacle lenses with aspherical lenslets: a 2-year randomized clinical trial. Invest. Ophthalmol. Vis. Sci. 2021;62(8):2888.
- Wolffsohn JS, Kollbaum PS, Berntsen DA, Atchison DA, Benavente A, Bradley A, Buckhurst H, Collins M, Fujikado T, Hiraoka T, Hirota M, Jones D, Logan NS, Lundstrom L, Torii H, Read SA, Naidoo K. IMI – Clinical Myopia Control Trials and Instrumentation Report. Invest Ophthalmol Vis Sci. 2019;60(3):M132-M160.