Refer this article as: Decreton, B., LiveOptics: a unique approach to the design of Essilor lenses, Points de Vue, International Review of Ophthalmic Optics, N64, Spring 2011
LiveOptics: a unique approach to the design of Essilor lenses
A corrective lens is a technological product. Progress in this field has been based on two major research directions: physics-chemistry and optics. On the one hand, new functionalities are coming on the market: scratch-resistant, anti-reflective coating, dust-resistant, dirt-resistant, anti-rain and now anti-mist. These new performances are achieved thanks to a coating applied to the lens surface. The thinnest coatings measure less than a micron thick. Technologies involving the application of the coatings under vacuum have made great progress, pushed forward by the requirements of the electronics industry. On the other hand, surfacing and the calculation of lenses have undergone a technological revolution. The traditional manufacturing method uses tools, spherical or cylindrical in shape, enabling them to generate simple surfaces to provide the required prescription. Digital surfacing, using a diamond tool steered by digitally controlled motors, is able to generate extremely precise and complex surfaces. These new possibilities are radically transforming the way in which progressive lenses are designed and manufactured.
The progressive lens provides its presbyopic wearer with clear vision at all distances, requiring surfaces of complex geometry. In traditional manufacturing methods, a mould is first made that contains, so to speak, the negative of the surface one wants to create. The end quality of the lens depends to a large extent on the precision of the progressive mould made. Mould manufacturing processes have evolved enormously. The most recent methods are based on computer-driven digital tooling. They ensure matchless precision and reproducibility. This process means that semi-finished progressive lenses are made in large numbers with these moulds. The lens finishing operation, to adjust it to the exact prescription of its wearer, takes place in the prescription laboratory, close to the delivery point, and involves simple surfaces.
The arriving of digital surfacing in prescription laboratories is set to create upheaval in the traditional model. Progressive surfaces can now be generated individually, once the order is received by the laboratory.
Fig. 1: Digital surfacing machine
The first change is in terms of logistics. In the traditional method, all the technological complexity involves the mould. The skill of the designer of the progressive lens is, to a certain extent, frozen in this object. Henceforth it will be in the calculation software used for the surfaces to be created in the prescription laboratory.
The second change involves quality control. Checking of a progressive surface is a complex operation that requires highly developed skills and equipment. Checking of progressive moulds is performed centrally, meaning that the necessary equipment and expertise can be concentrated. Here, optical controls performed in the laboratory involve prescription compliance. Digital surfacing now requires quality control of each progressive surface generated in the prescription laboratory. Process checking is therefore an absolute necessity in order to ensure compliance of the lens produced.
Finally, the mould is intended to produce progressive lenses for a certain range of ametropias, i.e. an interval of spheres and cylinders. In this case, the design is calculated to function for this range of prescriptions. Henceforth the designer is in an entirely new configuration: when the lens is calculated he knows for which wearer it is intended, meaning that new possibilities are opened up.
But digital surfacing is only a method for creating surfaces. It is only when it is combined with advanced calculation methods that it can bring about additional performance.
Although they are technical items, lenses are intended to correct vision. Technological skill alone is not sufficient because the lens must interact with the eye and the wearer's visual system in order to enable him to regain clear, comfortable vision. Essilor uses a unique lens design approach known as Live Optics, which combines unique technological know-how with a knowledge of physiology. This twofold approach means that Varilux lenses can offer performance levels that are matchless on the market because the end wearer is put at the heart of the design approach. Only products recognised as being superior by wearers are put on sale.
The use of digital surfacing is at the heart of this approach. It means that consumers can be offered products that are ever more pleasant to use:
- So-called generic products that offer natural vision all day long, in all circumstances.
- Products dedicated to a specific activity. Knowledge of wearers' visual behaviour during a given task means that ultra high performance lenses can be created for people with sustained activity in terms of driving, computer work or even sport, for example. During sustained activity, this type of task is demanding for vision and requires an adapted optical solution.
- "Ethnic" products: physiological studies show that visual requirements vary between ethnic groups. On the one hand the way in which the frame is positioned on the face is not the same because morphology is different. On the other, visual behaviour can vary. Thus, reading distances depend on the characters that we are reading. Chinese ideograms, for example, are more demanding in terms of visual acuity and require a shorter reading distance. Essilor therefore sells adapted versions of its products in Asia (Azio range) and in India (India range).
However, the use of advanced technologies has meaning only if it meets the expectations of wearers. Among their requirements there isa high expectation for visual precision. Developed for astronomical research, wavefront technology has been adapted for use in ophthalmic optics by Essilor. It means that the entire light beam crossing the wearer's pupil can be taken into account, thus drastically reducing the level of high order aberrations on the lens. Wearers benefit from highly precise vision and better contrast. With Varilux Physio 2.0, modelling of wearers' pupil diameter means a guarantee of performance levels, even in very dim light conditions, a situation described by presbyopics as being the most difficult. This is real progress for consumers, made possible by skill in the afore-mentioned technology.
Going still further, Varilux is developing personalised progressive lenses, which are increasingly adapted to wearers' visual behaviour. The digital chain now extends into the store, with instruments intended to measure individual parameters directly on the intended wearer. This data is introduced when lenses are calculated. Thanks to years of research undertaken into physiology, Essilor is now the only manufacturer to offer lenses that take account of the dynamic visual behaviour of wearers, as is the case with Varilux Ipseo, a personalised progressive lens which is adapted to the way in which the wearer moves his eyes and head in order to offer a unique, perfectly well adapted solution.
Essilor has recently introduced Eyecode technology, which is an exclusive, patented measurement method. The exact position of the rotation centre of each of the two eyes is defined in three dimensions in just a few seconds. This point plays a key role in the calculation of any kind of ophthalmic lens, it is, to a certain extent, the optical reference point because it is around this point that the eye turns. Lens structure depends on its actual location: the position of long and near vision zones, field widths, etc. In the past its position was approximated by statistical models. It is not actually measured by the optician or optometrist.
Fig. 2: Eyecode: actual measurement of the eye's rotation centre means that lenses can be personalised precisely. This point is an optical reference.
The digital chain begins in the store. Opticians and optometrists are therefore playing a key role in this transformation of ophthalmic lenses. Using the digital instruments they have available to them they collect the data that enables the personalisation of lenses for their patients.
Essilor is addressing the future of ophthalmic optics supported by two pillars:
- An in-depth study of the visual system: an absolutely exceptional mechanism has been developed by research teams, the virtual reality lens simulator. This system is capable of representing in 3D and in real time the optical effects that a corrective lens would produce. This system, which is unique in the world, can be used to evaluate product potential even before the manufacture of prototype lenses. Product development times are shortened and new directions can be explored.
- Skill in the most advanced technologies: recent work shows that judicious usage of the two sides of the lens can result in the attainment of matchless performance levels. This approach, which is exclusive to Essilor, will not fail to bring a new standard for performance levels to the market in the very near future.
Fig. 3: The use of virtual reality in Essilor laboratories means that new concepts can be explored, with a reduction in the time required for putting new products on the market.
The creation of lenses that are ever more personalised and high performance also implies the availability of the right measuring instruments in stores. The role of the optician or optometrist is of overriding importance in this approach. Lens quality relies on their know-how and on the parameters they measure.