Is peripheral vision and reading speed affected by aspherical lenslet spectacle lenses?

Paper title: The impact of spectacle lenses for myopia control on visual functions

Authors: Yi Gao (1), Ee Woon Lim (1), Adeline Yang (1), Bjorn Drobe (1), Mark A Bullimore (2)

1. Research & Development, Vision Sciences AMERA, Essilor International, Singapore, Singapore.
2. College of Optometry, University of Houston, Houston, Texas, USA.

Date: Sep 2021

Reference: Gao Y, Lim EW, Yang A, Drobe B, Bullimore MA. The impact of spectacle lenses for myopia control on visual functions. Ophthalmic Physiol Opt. 2021 Nov;41(6):1320-1331

[Link to open access paper]

This study assessed the peripheral visual performance and reading speed for wearers of HAL (highly aspherical lenslet) and SAL (slightly aspherical lenslet) spectacle lenses designed for myopia control in children. Both lenses feature aspherical lenslets in concentric rings around a 9mm clear central zone.

Adults aged between 19 and 47yrs old with healthy eyes and refractive errors ranging from +1.75D to -8.50D participated in the study.

Of the pool of 28 participants, between 8-10 took part in one or more of 5 different experiments where the HAL and SAL lenses were compared to a single vision control lens.

The visual performance of the lens designs was evaluated by assessing:

1. Foveal visual acuity through lens periphery
   • A single Landolt ring was a fixation point at 3m under 100 and 10% contrast conditions
   • The subjects indicated the direction of the rings and their responses were converted to a logMAR acuity acuities
2. Foveal reading speed through the lens periphery
   • The subjects needed to recite total sentences displayed on a screen at 40cm at 100% and 10% contrast background
   • Their reading speed was measured in words per sentence
3. Peripheral motion detection (Gabor patches)
   • The task was to fixate on a cross in the centre of a screen at 42cm while a Gabor patch was presented at 26° eccentricity within the visual field
   • The contrast varied, starting at 100%
4. Peripheral motion detection (Cardinal motion)
   • 360 randomly positioned dots were presented at 42cm and moved at 4° per second either expanding, contracting or moving clockwise or anti-clockwise within the visual field
   • Fixation was on a central circle was needed while identifying the direction of the motion with a contrast of 100%
5. Useful field of view
   • This assessed visual attention and the ability to discriminate objects on a dark background screen centrally, peripherally and then peripherally with other visual distractions being present

Under high contrast conditions, the HAL or SAL lens designs did not significantly affect the visual acuity through the lens, the reading speed or peripheral vision motion detection.

With 10% low contrast conditions, the HAL lens design reduced acuity by 0.14logMAR (approximately 1.5 lines). The SAL design reduced acuity by 0.10logMAR (approx. 1 line). HAL also impacted reading speed at low contrast more than single vision.

There was no significant difference found between the HAL, SAL and single vision lens types for peripheral motion or for useful field of view (tests for visual attention).

Overall, the HAL design was shown to have no clinically significantly effect on peripheral visual performance or high contrast acuity and reading speed, when tested in adults.

1. The HAL lens was designed with the intention of being used in myopia control for children. Although this study recruited adult participants for the peripheral visual function experiments, another study¹ measured the optical quality and contrast sensitivity function of the HAL and SAL designs for myopic children and found the real-life impact of slight visual acuity and contrast sensitivity loss was likely to be negligible.
2. The HAL design did give slightly reduced visual acuities and reading speed through the lens periphery in low contrast (10%) conditions. However, the word size in the reading task was close to the low contrast acuity threshold, indicating that this was a difficult test to do. Typical reading and peripheral vision use would be in high contrast conditions and with larger word sizes for children. Additionally, head movement could also see some of the central clear zone of the lens being used for some of these tasks.
3. Most myopia is found to develop after the critical period of visual development.² Given that the novel lens designs were found to have little to no influence on peripheral visual function or reading speed in adults, it could be presumed to perform at least as well in children without significant concern for impact on visual development.

The HAL and SAL lenses were compared to a single vision lens in this study

• One study¹ has examined the short-term visual performance differences between HAL aspherical lenslet design and a lens design with spherical lenslets in a honeycomb configuration. Although there was a slight visual acuity reduction from lenslet designs compared to a single vision lens, HAL and SAL designs were shown to impact the visual acuity less than honeycomb arrangement lenses.
• It would be interesting to compare the peripheral visual performance of myopia control spectacle lenses now available in children, however the methodology of testing may be difficult for this participant age group.

Title: The impact of spectacle lenses for myopia control on visual functions

Authors: Yi Gao, Ee Woon Lim, Adeline Yang, Bjorn Drobe, Mark A Bullimore

Purpose: Spectacle lenses containing multiple small peripheral elements have been developed for myopia control in children. It is important that their effect on vision be quantified by (i) fixation through the peripheral portion, thereby using foveal vision and (ii) by fixation through the central portion and presentation of peripheral targets.

Methods: The above approaches were used in five studies to evaluate two novel spectacle lens designs: spectacle lenses with Highly Aspherical Lenslets (HAL) and Slightly Aspherical Lenslets (SAL). A single vision lens served as a control. Visually normal adults participated in each study. The first two studies had subjects fixate through the periphery of the lenses. High and low (10%) contrast visual acuity was measured with the Freiburg Vision Test and reading speed for high and low contrast words measured with a sentence generator. The other three studies assessed peripheral vision while subjects fixated through the central portion of the lens.  Peripheral contrast sensitivity was measured using two cycles per degree drifting Gabor stimuli. Peripheral motion perception was further evaluated using random dot stimuli. Finally, attention was measured using an established test of useful field of view with three levels of complexity.

Results: The periphery of the HAL lens significantly reduced low contrast visual acuity, but not high contrast visual acuity, while the effect of the SAL lens was not significant for either. Neither test lens affected reading speed for high contrast words, but the HAL lens significantly affected performance for low contrast words. Neither test lens affected peripheral motion perception or useful field of view

Conclusions: Low contrast visual acuity and reading was slightly reduced while high contrast visual acuity was unaffected when fixating through the periphery of the novel lens designs. None of the peripheral measures of vision was affected by the novel lens designs

[Link to open access paper]