One-year myopia control efficacy of spectacle lenses with aspherical lenslets

Paper title: One-year myopia control efficacy of spectacle lenses with aspherical lenslets

Authors: Jinhua Bao (1,2), Adeline Yang (2,3), Yingying Huang (1,2), Xue Li (1,2), Yiguo Pan (1,2), Chenglu Ding (1,2), Ee Woon Lim (2,3), Jingwei Zheng (1), Daniel P Spiegel (2,3), Björn Drobe (2,3), Hao Chen (1,2)

1. Eye Hospital and School of Ophthalmology and Optometry, Wenzhou Medical University, Wenzhou, Zhejiang, China
2. Wenzhou Medical University–Essilor International Research Center (WEIRC), Wenzhou Medical University, Wenzhou, Zhejiang, China
3. R&D AMERA, Essilor International, Singapore

Date: Apr 2021

Reference: Br J Ophthalmol. 2021;Apr 2:bjophthalmol-2020-318367. [Link to open access paper]

This new innovation in myopia controlling spectacle lens technology uses aspheric lenslets to "creates a three-dimensional quantity of light in front of the retina, which we call volume of myopic defocus (VoMD) in this paper." Each lenslet is 1.1mm in diameter and "11 concentric rings are formed [across the lens] by  contiguous aspherical lenslets.

Chinese children (n=170) aged 8-13 years with myopia of -0.75D to -4.75D  were randomized into either single vision, highly aspherical lenslet (HAL) or slightly aspherical lenslet (SAL) spectacle lenses. After one year, myopia progressed -0.81D/0.36mm in SV, -0.48D/0.25mm in SAL and -0.27D/0.13mm in HAL. This represented around a 60-70% refractive and axial length efficacy for HAL and 30-40% for SAL.

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, and near phoria and accommodative lag, were unaffected by the lens designs on baseline measurement.

This one-year data shows robust myopia control of the HAL treatment spectacles, analogous to the efficacy seen in dual focus contact lenses and orthokeratology. The prospect of a myopia controlling spectacle with better efficacy than current progressive addition or bifocal spectacle lens options is clinically appealing.

Since myopia control strategies tend to show greatest efficacy in the initial stage of treatment,¹ longer term data is required - as this is an ongoing clinical trial this can be expected.

This is a robust randomized controlled trial with the outcome measures being gold standard - cycloplegic autorefraction and axial length measurement by interferometry (Lenstar LS900 instrument). The sample size was appropriately powered to detect hypothesized differences.

Future research directions

• Longer duration of the same clinical trial, which is planned for two years, to assess any alteration in the treatment effect over time. This will also permit direct comparison to the Defocus Incorporated Multiple Segments (DIMS) spectacle lens two year RCT.2
• Future trials in children of other ethnicities will be important to determine how generalizable these results are from those found in Chinese children.
• Verification of the differential optical effect of HAL and SAL at the retinal level, given that the different 'volume(s) of myopic defocus' have only been modelled so far.

To evaluate the 1-year efficacy of two new myopia control spectacle lenses with lenslets of different asphericity - highly aspherical lenslets (HAL) and slightly aspherical lenslets (SAL). 

This 2-year clinical trial was designed to be a randomized, controlled, double-masked study with follow-up visits every 6 months. This paper presented the planned 12 month interim analysis. Participants were:

• Aged 8-13 years
• Myopic with baseline spherical equivalent refractive error between -0.75 and -4.75D
• No more than 1.50D astigmatic
• No more than 1.00D anisometropic
• Monocular best corrected visual acuity of 0.05 (6/6-2or 20/20-2) logMAR or better in both eyes
• No ocular pathology or binocular vision issues, and no history of other myopia control intervention

The paper describes the use of aspheric lenses with a power gradient in animal studies. 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 three-dimensional 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."

• Measured at dispensing baseline, 6-months and 12-months:
  • Objective cycloplegic spherical equivalent refraction: Topcon KR-800, measured at least 30 min after instillation of two drops of 1% cyclopentolate administered 5 min apart
  • Axial length: Lenstar LS900 instrument using the average of 5 measurements
• Measured at dispensing baseline only:
  • Near horizontal phoria (33 cm, modified Thorington technique)
  • Lag of accommodation (33cm, monocular measurement under binocular viewing conditions, using Grand Seiko WAM-5500 open field autorefractor)
  • Distance best corrected visual acuity (BCVA) using multifunction VA tester
  • Near BCVA at 40cm using 100% contrast ETDRS.
• Phone interview after 3 days and 2 weeks after dispensing to ensure and record adaptation outcomes
• Questionnaire to assess wering time and compliance administered at 6-months and 12-months.

After one year, myopia progressed -0.81D/0.36mm in SV, -0.48D/0.25mm in SAL and -0.27D/0.13mm in HAL. This represents around 60-70% efficacy for HAL and 30-40% efficacy for SAL, and an absolute effect of 0.54D/0.23mm less myopia for HAL wearers and 0.33D/0.11mm less myopia for SAL wearers after 12 months.

Axial length was stable over the one year study in 28% of the HAL group, 9% of SAL and 0% of SV groups.

A younger age and early age of myopia onset were correlated with greater axial length change in the SV and SAL groups, but not in the HAL group, indicating a robust myopia control effect of the HAL lens in younger children.

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 at baseline - follow up data on this is not presented.

Daily wearing time was self-reported as around 13 hours in each group. Within 3 days, on telephone questionnaire, 90% of HAL, 100% of SAL and 94% of SV wearers reported being adapted to their lenses, with no significant difference between teh group. All wearers were self-reportedly adapted within a week. No adverse events related to the interventions were reported.

Results from this study reveal an innovative new option for myopia controlling spectacle lenses with, the one-year data on HAL efficacy comparable to DIMS spectacle lenses,² dual focus soft contact lenses³ and orthokeratology.⁴ Completion of the two year clinical trial will provide a similar level of data to these other interventions to allow more accurate comparison.

Paper title: One-year myopia control efficacy of spectacle lenses with aspherical lenslets

[Link to open access paper]