New vision needs for near vision and beyond
Generation X – those who are born between 1965 and 1980 – have very different vision requirements from their elders. They’re no longer reading at one (single) near distance; instead, they use their entire near space to carry out multiple activities with near vision up to arm’s length. The advent of digital tools like computers, tablets and smartphones has radically transformed their near-vision needs. These presbyopes aren’t just reading; they’re also performing multiple tasks at a near-intermediate distance between 40 and 70 cm: they’re working on a computer screen, reviewing documents, typing on a keyboard, watching videos, answering their mobile phone, writing text messages, sharing data with friends and family, etc. Their vision is dynamic and involves numerous distances. They need to be able to shift smoothly from one task to another, without being held back by their vision.
The Varilux® X seriesTM lens has been designed to offer these wearers an extended near vision within arm’s reach that meets their needs more effectively than a conventional progressive lens, Fig 1. This article will take a look at the methodology that was used to study these wearers’ needs and describe the features of the new generation of progressive lenses: Varilux® X seriesTM.
FIG. 1 The changing needs of presbyopic wearers: a single near distance versus multiple near distances.
A new way of studying wearers’ needs
A multi-disciplinary team came together with the aim of gaining a better understanding of this new generation of wearers. The team’s members studied expectations and behaviour among wearers and developed new research methods for observing their day-to-day experience as closely as possible.
Specialists from a variety of disciplines, including ergonomists, physiologists, sociologists and optics designers, joined forces to learn more about these wearers’ needs, both as presbyopes and consumers.
They drew on a range of new research resources, including:
- a test house, the HouseLabTM, where consumers were observed and interviewed while immersed in a natural – but controlled – environment in which they could perform routine daily activities;
- a laboratory for evaluating wearers’ behavior, the Essilor’s Movis Laboratory. This lab is used to capture wearers’ posture and movements in real time as they perform simple tasks such as working on a computer, reading on an e-reader, writing e-mail, playing video games, watching videos on a tablet, reading and writing text messages on a smartphone, and so on.
These new techniques provided insights into each wearer’s needs, Figure 2 – insights that were then used to design this new progressive lens.
FIG. 2 Research work on the vision needs of Generation X and insights.
An extended near vision within arm’s reach
In the past, progressive lens design were merely taking into account the need for distance vision (beyond 3 m), near vision (about 40 cm) and intermediate vision. By observing the new generation of wearers, researchers identified an array of new vision needs in the area up to 70 cm – so-called arm’s-length vision – that falls between near-distance and intermediate vision. While the near vision portion of the lens (where the add power is at least 85%) had already been studied extensively, the portion used for near- intermediate or arm’s-length vision (where the add power is 60% to 85%) has not been as heavily researched, and the researchers gave that area special attention.
« By observing the new generation of wearers, researchers identified an array of new vision needs in the area up to 70 cm – so-called arm’s-length vision – that falls between near- distance and intermediate vision. »
Initially, the study aimed to define the levels of visual acuity needed for each distance. Researchers found that comfortable reading at a distance of 40 cm required a visual acuity of 0.1 Log MAR (or 8/10 or 6/7,5 or 20/25) or above, while at 70 cm an acuity 0.15 Log MAR (or 7/10 or 6/8,5 or 20/28,5) at least is adequate and between 50 and 70 cm the acuity requirement gradually changes from 0.10 to 0.15 Log MAR thresholds .
The lens designers then used a sophisticated new calculator that uses an “acuity model”, which can be used to simulate the combined effect of the lens power and astigmatism on the wearer’s visual acuity at any point on the lens, based on the proximity of the objects viewed and the wearer’s remaining amplitude of accommodation. The results were expressed in the form of visual acuity plots like the one shown in Figure 3. It shows how visual acuity is affected by the lens’s optical properties for each gaze direction, ranging from the central portion of the lens, where acuity is at its highest, to the periphery, where it deteriorates. The natural dynamics of head movement obviously allow wearers to maintain their gaze in the centre of that area of acuity. The relationship between add power and astigmatism and the visual acuity used to calculate these maps were determined on the basis of the test measurements performed on a group of wearers.
FIG. 4 Xtend™ technology: management of multiple targets for the same gaze direction.
The area of the lens corresponding to arm’s-length vision, located between the near vision zone and intermediate vision zone, was defined as the area of the lens where the power varies between 60% and 85%. To improve that area in particular, the lens designers used a new technique known as XtendTM technology (an innovation covered by 15 pending patents), as illustrated in Figure 4. It involves applying “acuity buffers” that locally curb vertical and horizontal variations in power so as to maximize field depth and expand the field of vision. In other words, the technique locally corrects aberrations in the lens in order to improve the wearer’s local field of visual acuity in terms of both depth and width. This technique uses the Nanoptix™ technology to apply this correction to seven adjacent micro-components simultaneously, taking into account the specific acuity levels to be maintained for each of those micro-components (Figure 5). This task is first performed along the meridian of progression on the lens and then in the area surrounding that meridian. Thus, by moving from one spot to the next, the performance and acuity of the lens progression zone can be greatly improved, while the near vision/intermediate vision zone is specially enhanced for arm’s-length vision.
FIG. 5 The various zones of vision on a progressive lens (expressed as a percentage of the add value): far vision (FV) from 0% to 15%, mid-distance vision (IV) from 15% to 60%, arm’s-length vision (ALV) from 60% to 85%, near vision (NV) from 85% to 100%.
Evaluating lens performance using “volume of acuity”
« Researchers introduced a new concept: the “volume of acuity” needed for comfortable vision. That refers to the volume of space that a wearer can perceive through the lens with the necessary visual acuity to perform typical tasks at each distance. »
To evaluate the performance of the Varilux® X seriesTM progressive lens, researchers introduced a new concept: the “volume of acuity” needed for comfortable vision. That refers to the volume of space that a wearer can perceive through the lens with the necessary visual acuity to perform typical tasks at each distance: reading with near vision, looking at a computer screen with arm’s-length vision, deciphering text with intermediate vision, etc. That volume, which had only rarely been identified in the past, indicates the wearer’s three-dimensional area of clear vision, with specific attention to the depth of the wearer’s field of vision.
Thus, if we compare the volume of acuity obtained with the Varilux® X seriesTM lens with that of an earlier progressive lens, we see (as shown in Figure 6) that the volume of vision is considerably enlarged both in width and depth, especially in the area of so-called arm’s- length vision. The XtendTM technology makes it possible to maintain visual acuity at a higher level than the threshold previously defined (0.15 Log MAR at 70 cm), with the result that wearers enjoy a significantly larger area of clear vision.
FIG. 6 Volume of acuity offered by the Varilux® X seriesTM lens compared to a Varilux® X seriesTM lens.
Moreover, the concept of the volume of acuity can also be used to quantify the overall performance of the lens in light of the wearer’s needs. If we compare the volume of clear vision provided by the lens with the volume of vision that the wearer needs, we can calculate a matching factor for the lens, i.e., a coefficient of correspondence to the wearer’s needs. Specifically, based on a series of vision tasks to be performed within arm’s length, at different distances and with varying acuity requirements, we can define an average “required volume” for wearers. We can then compare that volume to the volume of vision offered by the lens when the wearer is gazing into space and explore it with the accommodation and a fixed head. A ratio of those two volumes (vision volume/required volume) yields a coefficient that indicates the lens’s ability to fulfill vision needs.
Using that process, the Varilux® X seriesTM lens was found to satisfy 75% of the wearer’s needs for arm’s-length vision, compared to an average of 59% for other progressive lenses – an unprecedented level of performance (calculations performed by Essilor’s R&D, based on the standard design of the Varilux X Series in comparison with several progressive lenses available on the market).
Wearers have expressed a high level of satisfaction
As with all new progressive lenses from Essilor, the Varilux® X seriesTM lens was tested on a large group of wearers before it was commercialized. One of the following studies was conducted in accordance with an established, certified protocol that uses randomization and double-blinding. As can be seen from the results shown in Figure 7, wearers reported superior vision quality, which they considered better than that of a previous-generation progressive lens (Figure 7a). They also expressed a high level of satisfaction in using their new lenses for arm’s-length activities (Figure 7b). These studies provide evidence that this next-generation lens is a true advance over previous lenses, particularly for improving the area of near and intermediate vision.
FIG 7a) Vision quality compared to a previous-generation progressive lens (Varilux® X seriesTM)
FIG 7b) Wearer satisfaction during activities performed within arm’s length
With the Varilux® X seriesTM lens – the eighth generation of progressive lenses – Essilor is once again innovating to push the limits of progressive lenses and more effectively address the multiple near-vision needs of today’s presbyopes – especially those from Generation X, for whom this new Varilux lens is named. •
Note from authors: this article is an adaptation from a White Paper published by Essilor’s R&D.