How do different lenslet configurations in myopia control spectacle lenses influence visual performance?

Paper title: Influence of Lenslet Configuration on Short-Term Visual Performance in Myopia Control Spectacle Lenses

Authors: Xue Li (1,2,3), Chenglu Ding (1,2), Yuhao Li (1,2), Ee Woon Lim (3,4), Yi Gao (3,4), Bruno Fermigier (5), Adeline Yang (3,4), Hao Chen (1,2,3), Jinua Bao (1,2,3)

1. Eye Hospital and School of Ophthalmology and Optometry, Wenzhou Medical University, Wenzhou, China
2. National Clinical Research Centre for Ocular Diseases, Wenzhou, China
3. Wenzhou Medical University- Essilor International Research Centre (WEIRC), Wenzhou, China
4. R&D AMERA, Essilor International, Singapore, Singapore

Date: May 2021

Reference: Li X, Ding C, Li Y, Lim EW, et al. Influence of Lenslet Configuration on Short-Term Visual Performance in Myopia Control Spectacle Lenses. Front Neurosci. 2021 May 25;15:667329. [link]

This study evaluated visual performance and optical quality through various lenslet configurations in 50 myopic children. 4 lens designs were used; 1 single vision lens, 2 lens designs with concentric rings of highly aspherical lenslets (HAL) and slightly aspherical lenslets (SAL); and 1 lens design with honeycomb configuration of spherical lenslets (HC). All 3 designs degraded short-term visual performance in some capacity, with concentric ring design (HAL and SAL) generally having a significantly lower impact on both visual acuity (VA) and contrast sensitivity (CS) than honeycomb configuration (HC). 

When viewing through the lenslet zones, the HC design resulted in a significantly worse reduction in VA (0.09 ± 0.07 logMAR, approx 1 line) than the other two designs, however the difference in VA between HC and HAL and SAL (0.02 and 0.03logMAR respectively) correlates to an approximate 1-2 letter difference, which is unlikely to be clinically significant. CS was reduced by all 3 configurations of lenslets, with the greatest loss in HC. At both photopic and mesopic levels, HC reduced CS at high spatial frequencies more than SAL and HAL. Objective visual quality, measured by MTFa (modulation transfer function area) was larger in HAL and SAL than HC, indicating the lenslets of concentric ring configurations may provide superior optical performance. All lenslet designs reduced mid- and high-spatial frequencies somewhat. Very high spatial frequencies were reduced with HC but not with HAL and SAL configurations.

The impact of HAL and SAL on VA and CS was similar across all conditions, indicating that the magnitude of asphericity of the lenslets had little effect on visual performance. Glare had minimal impact on visual performance compared to low illumination conditions.  

Importantly, this study tested central vision through the lenslet zones, which would be the view through the spectacle lens periphery without a patient turning their head to use the single-vision central zone of the lens. The overall findings here of small impacts on visual performance could therefore be potentially even less with natural head turns to see in the periphery that take in the central zone for viewing.

Clinically, this provides insight into the visual experience of wearing spectacles with lenslets, which can be expected to only have small impacts on visual performance in children in typical viewing conditions. Two of the lenslet configurations tested - HAL and HC - are commercially available as myopia control spectacle lenses. 

An interesting outcome was that visual acuity through the lenslet zones of each spectacle lens design was minimally affected by the presence of glare. Low illumination had more of an impact. This provides useful guidance on patient expectations for the wearing experience.

We still need to determine if the impact on visual performance and optical quality reported here is clinically relevant for young wearers. It is unlikely that there will be a clinically significant impact if these lenses are worn appropriately (with lenslets in periphery vs centrally, as in this experiment) and an adaptation period is given. Further research on long-term adaptation of visual functions would be useful. 

Title: Influence of Lenslet Configuration on Short-Term Visual Performance in Myopia Control Spectacle Lenses

Authors: Xue Li, Chenglu Ding, Yuhao Li, Ee Woon Lim, Yi Gao, Bruno Fermigier, Adeline Yang, Hao Chen, Jinua Bao

Purpose: This study aimed to evaluate short-term visual performance and optical quality of three different lenslet configurations on myopia control spectacle lenses.

Methods: This study utilized a cross-over design. Distance visual acuity (VA) was measured in 50 myopic children; contrast sensitivity (CS) was measured in 36 myopic children. For each test, four spectacle lenses were evaluated in a random order: single-vision lens (SVL), lens with concentric rings of highly aspherical lenslets (HAL), lens with concentric rings of slightly aspherical lenslets (SAL), and lens with honeycomb configuration of spherical lenslets (HC). The modulation transfer function (MTF) and MTF area (MTFa) were used to determine optical quality. All tests were performed monocularly on the right eye with full correction.

Results: HAL and SAL had larger MTFa than HC. VA in lenses with lenslets was significantly reduced compared to SVL (all < 0.01). The reduction in VA was worse with HC than with SAL ( = 0.02) and HAL ( = 0.03); no effect of lenslet asphericity was found (p > 0.05). VA changes induced by lenslets showed no correlation with spherical equivalent refraction (all p > 0.05) and were weakly positively associated with age for SAL (r = 0.36, p = 0.01) and HC (r = 0.31, p = 0.03), but not for HAL (p = 0.30). The area under the log contrast sensitivity function (AULCSF) decreased with HAL and HC (all p < 0.001) in all illumination levels, and AULCSF with HAL was higher than that with HC in a photopic condition (1.17 ± 0.10 vs. 1.10 ± 0.13, p = 0.0004). The presence of lenslets did not affect CS at 3 cycles per degree (cpd) (p = 0.80). At 6 to 18 cpd, CS was significantly reduced by HAL and HC (all p < 0.05), but not SAL (p > 0.05) compared to SVL. At high spatial frequencies (>12 cpd) both SAL and HAL reduced CS significantly less than HC (all p < 0.01).

Conclusions: Short-term visual performance was minimally impaired by looking through the lenslet structure of myopia control spectacle lenses. Concentric rings with aspherical lenslets had a significantly lower impact on both VA and CS than honeycomb configuration with spherical lenslets.

[Link to open access paper]