A driving simulator as a tool for benchmarking optical lenses

A driving simulator as a tool for benchmarking optical lenses

Pixabay:ID 12019

Conception of the Aalen Mobility Perception & Exploration Lab (AMPEL)

The Aalen Mobility Perception & Exploration Lab (AMPEL) is part of the Competence Center “Vision Research” in the Innovation Centre (Inno-Z) at the University of Applied Sciences in Aalen, Germany. A virtual research environment was developed there, which allows for night driving experiments under highly standardized conditions. This also allows for benchmarking optical lenses.
By Judith Ungewiss, Michael Wörner, Ulrich Schiefer

About one third of all road traffic accidents occurs at night. This seems to correspond to the percentage of the dark period on a superficial view. However, taking into account that only approximately 25% of the yearly mileage is driven at nighttime, the risk of a traffic accident with a fatal outcome is increased by about 50 % at night in comparison to the same distance traveled during the day (data collected for the Federal Republic of Germany) [1][2]. Nighttime driving ability is therefore of specific importance in road traffic.
With regard to the effort involved in setting up a driving simulator, the question as to whether this is worthwhile in order to determine the ability for night driving arises. In this respect – even though we feel that the value of each human life is “inestimable” and thus cannot be quantified in monetary terms – it should be noted that the statistical value of a (traffic) accident death in the Federal Republic of Germany is estimated at an average of about 4.5 million Euros [3]. In comparison, the costs for driving simulator experiments, which in the best case contribute to saving human lives in the future, seem manageable and legitimate. Furthermore, such a simulator has the important advantage to display scenarios in a highly immersive way under standardized conditions (cited as in [4]).

Setup and interior of the Aalen Mobility Perception & Exploration Lab (AMPEL)

The Aalen Mobility Perception & Exploration Lab (AMPEL), operated by the Competence Center “Vision Research” in the Innovation Centre (Inno-Z) on the campus of the Aalen University of Applied Sciences, was launched in 2015 and consists of two large laboratories with associated measurement and workstations.

The nighttime driving simulator situated in the AMPEL lab contains a completely retrofitted Audi A4 (Audi AG, Ingolstadt, Germany) with a steering and pedal unit (SensoDrive GmbH, Wessling, Germany), and two fully digital displays (instrument panel and navigation monitor). Two high-performance projectors (Zeiss Velvet 1600, Zeiss AG, Jena, Germany), which are commonly used in a planetarium environment, project the driving route on a cylindrical 180° screen with a radius of 3.20 m. A monitor (KD 65 XF 9005 BAEP, Sony, Tokyo, Japan) behind the trunk of the car provides an almost realistic scenario through the rear-view mirror. A vehicle can be brought into the laboratory via a sliding window and, if necessary, be exchanged for another vehicle or another test arrangement (see Fig. 1 and Fig. 2). Driving scenarios are imported using the SILAB simulator software developed by the WIVW (Würzburg Institute for Traffic Sciences, Veitshöchheim, Germany). It is possible to visualize traffic routes using existing GPS data.

@image: Fig.1 hier

@image: Fig.2 hier

Speed-related driving noise can be generated by a loudspeaker (BeoPlay Beolit 15, Bang & Olufsen, Struer, Denmark). This noise acts as an acoustic feedback and therefore supports the patients with regard to velocity control while driving.

Calibration procedures are regularly executed prior to the start of a study (Spectroradiometer CAS 140 VIS/UV, Instrument Systems GmbH, Munich, Germany and Minolta Luminance Meter LS160, Konica Minolta Holdings K.K., Tokyo, Japan).

@subhead: Simulator vs. on-road experiments
Why are experiments not directly implemented in the form of (real) on-road driving, but instead a simulator is set up with a great deal of effort with the aim of creating a driving environment as close to reality as possible?
The main reason for this is the complexity and thus usually inadequate standardization of the on-road experiments: It is almost impossible to realize identical conditions with respect to the road surface, weather, lighting, wind conditions etc. for several experimental runs (which may additionally also be executed on different days). The personnel expenditure for on road experiments is also considerable: On the routes used, the street lighting may have to be switched off, and the routes must be locked by roadblocks or supervisory staff so that passers-by do not endanger themselves or the experiments. Additionally, for insurance reasons, such experiments are only permitted in a vehicle with a dual brake system set under the constant supervision of a driving instructor. Experiment supervisors and operators (responsible for the technical implementation of the experiments) are required.
On the other hand, only one test supervisor and one operator are required to carry out the corresponding experiments in a simulator. A driving simulator allows for highly standardized examinations without compromising the safety of test persons [4].

@subhead: Technical and experimental opportunities
The driving simulator in the AMPEL laboratory realizes the determination of visual acuity and contrast sensitivity also while driving. Individual local thresholds are assessed by eight-position Landolt Cs. The stimuli can be presented at various locations under different distances within the setup:
• at the projection screen (right road side, 4.66 m)
• at the monitor just behind the trunk via the center of the rear-view mirror (3.40 m)
• at the center of the navigation monitor (0.75 m)
• at the center of the instrument panel (distance 0.72 m) (see Figure 3).

@image: Fig. 3 hier

The appearance of the visual signal can be announced to the test participant with an audio signal. The opening of the appearing Landolt C has to be indicated (verbally) by the test person and is recorded by the test supervisor or – as an alternative – by a miniaturized microphone. In this way it is possible not only to check the correctness of the respective response but also to record its latency. Beyond Landolt Cs, obstacles (e.g. pedestrians or animals, each with various contrast levels) can be presented.

The simulator is equipped with an eye tracking system (SmartEye Pro, sampling rate 120 Hz, gaze accuracy of 0.5° under ideal conditions, SmartEye AB, Gothenburg, Sweden), which enables the contact-free recording and evaluation of head and eye movements. For this purpose, the driver is observed via (a minimum of) three infrared cameras while driving. The driving scenario is recorded by an additional scene camera. With the help of this set up, head and eye movements as well as fixations of the driver can be assigned and annotated to certain objects or regions of interest.

A realistic display of glare, for example from headlights of oncoming vehicles, is an essential factor for the representation of a close-to-reality driving environment. Simply projecting virtual headlights on the screen of the simulation environment does not achieve the necessary luminance values. Instead, a patented mobile glare device was developed for the AMPEL laboratory: With the help of cable robots, wireless LED arrays controlled via WiFi are moved in both, horizontal and vertical directions. The power supply is provided by small lithium-polymer accumulators, as used in model aircraft constructions [4].

In order to validate such a simulator, it has to be determined whether a virtual scenario actually measures what it is supposed to measure. Such validation is achieved by comparing the simulator results with those of a real on-road driving test under comparable conditions.
At the AMPEL lab, the on-road parcours of the “Burren” campus at the Aalen University, next to the driving simulator, is transferred into its virtual environment by using the Software package SILAB (Würzburg Center for Traffic Sciences, WIVW, Veitshöchheim, Germany) [4].

@subhead: Benchmarking optical lenses
Optical lenses are usually evaluated by ray tracing methods or questionnaires: Ray tracing is well suited to characterize the image quality at the retina level whereby the image processing in the subsequent visual pathway is not taken into account. Questionnaires are subjective tools with an inherent lack of standardization.

A new, patented approach was set up at the AMPEL laboratory: A psychophysical test records the individual’s visual performance or impairment in a location-specific manner within the highly standardized environment of a driving simulator. LED arrays that are either static or moving via cable robots serve as glare sources [5]. Static and dynamic optotypes, moving along so-called vectors with a constant angular velocity, are presented for this purpose. The vector origins can be placed within the center of a glare source (current setup: Visual angle: 0.3°, luminance level 60 kcd/m2, 6.2° left of and 1.1° below the fixation mark, corresponding to the left headlight of an oncoming car [GOLF VII, Volkswagen AG, Wolfsburg, Germany]). By this way the individual, location-related extent of the visual impairment due to halo or starburst can be assessed (see Figure 3). Local threshold variability and individual response time are assessed by repeated presentations and vector placements within unaffected visual field areas on meridians 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315° (in random order).
The extent of the displacement of the isopters during the glare condition, compared to the initial condition without glare represents the magnitude of impairment due to glare / halo size (see Fig. 4) [6]. Patient responses can be recorded in order to extract reaction times either from these recordings or from the keypad inputs.

The setup is being used for characterizing the visual effects of media opacities (cataract) in motorists (ContrastVal study, ClinicalTrials.gov Identifier: NCT03169855) for benchmarking the impact of any kind of optical corrections, such as intraocular lenses (JJ-EYHANCE study, ClinicalTrials.gov Identifier: NCT04059289), spectacle lenses, contact lenses, or other (surgical) refractive procedures.

@image: Fig.4 hier

@subhead: Conclusions
In the AMPEL lab, a virtual test environment was created which allows for night driving experiments under highly standardized conditions. By means of visual acuity or contrast vision testing under static or dynamic conditions and at various locations, benchmarking optical lenses can be achieved. In addition, static or dynamic blinding of the test subjects with simultaneous time-resolved visual function testing is possible. In comparison to real on-road experiments, simulator experiments are safe, well-standardized and require a comparatively low effort. A validation is possible if required.

[1] Kraftfahrtbundesamt. Erneut mehr Gesamtkilometer bei geringerer Jahresfahrleistung je Fahrzeug. https://www.kba.de/DE/Statistik/Kraftverkehr/VerkehrKilometer/2017_vk_kurzbericht_pdf.pdf?__blob=publicationFile&v=14. Updated April 18, 2020. Accessed April 18, 2020
[2] Statistisches Bundesamt (Destatis). Verkehrsunfälle Zeitreihen 2017. 2018
[3] Spengler H. Kompensatorische Lohndifferenziale und der Wert eines statistischen Lebens in Deutschland. Zeitschrift Arbeitsmarktforschung 3:269–305. 2004
[4] Ungewiß J, Schiefer U, Wörner M. Untersuchung der Nachtfahrtauglichkeit im Simulator – Vorstellung des Aalen Mobility Perception & Exploration Lab (AMPEL). Der Augenspiegel 06/2019:38-41. 2019
[5] Eichinger P, Sauter T, Schiefer U, Schmitt U, Ungewiss J, Hirche M, Schuster M. Fahrsimulator und Verfahren zur Durchführung einer Fahrsimulation. German Patent and Trademark Office: Patent 10 2017 126 741, IPC G09B 9/02
[6] Schiefer U, Ungewiss J, Wörner M. Ortsbezogene Quantifizierung von Halo- und Streulichtbeeinträchtigung. German Patent and Trademark Office: Patent 10 2019 121 602 A1, WO 2020/089284 A1

The authors would like to thank Prof. Dr. Peter Eichinger, Prof. Dr. Ulrich Schmitt and their whole ContrastVal study team (Mechatronics, Aalen University, Germany) for the design and implementation of the glare sources and Prof. Dr. Jürgen Nolting and Prof. Dr. Günter Dittmar (AWFE Steinbeis Transfer Centre, Aalen, Germany) for their comprehensive support in light measurement tasks.

Disclosure of financial and proprietary interests:
Ulrich Schiefer is consultant of the Haag-Streit AG, Köniz, Switzerland.
Michael Wörner is Managing Director of Blickshift GmbH, Stuttgart, Germany.


Corresponding author:
Judith Ungewiss – judith.ungewiss@hs-aalen.de
Judith Ungewiss holds a M.Sc. in Ophthalmic Optics & Psychophysics. She works as scientific assistant in the Competence Center “Vision Research” in the study course ophthalmic optics & audiology at Aalen University.
@image: Judith_Ungewiss

Dr.-Ing. Michael Wörner is a software engineer who works as scientific assistant in the Competence Center “Vision Research” in the study course ophthalmic optics & audiology at Aalen University. In addition, he is Managing Director of Blickshift GmbH in Stuttgart, Germany.
@image: Michael_Wörner

Prof. Dr. med. Ulrich Schiefer is head of the Competence Center “Vision Research” (study course Ophthalmic Optics at Aalen University), which addresses the visual system and its possible dysfunctions, especially regarding the development and validation of examination and therapy procedures. After his medical studies and service in the Dept. of Ophthalmology at Military Hospital Ulm, he joined the University Eye Hospital Tübingen in 1989 where he has filled various positions in a full-time appointment until 2012 and in a part-time scientific appointment up to now. Ulrich Schiefer holds several patents on perimetric examination technique and other mainly sensory physiological examination methods.

Infrared protection for sun protection lenses

Infrared protection for sun protection lenses

The sun

Any reduction of the light spectrum using filter lenses triggers a lot of discussion. Even with UV420 lenses, there are many arguments for and against in the market and some even ask the question whether the lens industry will soon recommend protecting the eyes by not letting in any more light at all. The simple background to this discussion is the continuously rising life expectancy of the population in developed countries and the understanding that for the foreseeable future it won’t be as easy to replace the “worn out part of the eye” as it is, for example, to replace a hip.

By Florian Gisch

While incidences of cataracts and AMD were characteristic of the later years of life in the 1950s, patients affected today are typically in the middle of their lives, possibly in a job and needing their eyesight more than ever to use digital media, smartphones, etc.

Thus all these efforts are simply aimed at keeping the harmful effects as low as possible over the entire lifetime, in order to delay the inevitable onset of signs of wear and tear to as old an age as possible.

Development of sun protection products

After initial suspicions that UV light could be harmful in the middle of the 19th century, Crookes sun protection lenses appeared in 1913, guaranteeing 100% UV light protection. In 1908 the Swiss ophthalmologist Alfred Vogt succeeded in proving its harmfulness. In 1926 he published his conclusions that ultraviolet light has a damaging effect on the eye, pointing out at the same time that infrared radiation was likely to have a similarly damaging effect.

In 1930, the first sunglasses were produced in series, with the main focus still on glare protection. In addition to the fashion aspect of sunglasses, protective standards such as the recently developed EN183 were introduced which speak of complete UV protection as soon as there is absorption of 95% in the range up to 380 nm. The more popular standard – which every end user knows – in the meantime is the UV400 quality seal, which also takes into account visible light and the amount of harmful high-frequency blue light blocked.

Infrared protection has received little attention so far up to now.

Interestingly, the same was true for infrared protection in the field of dermatology until the topic was rediscovered a few years ago. Far from a purely “marketing gimmick”, but from the field of environment-related molecular aging research, the development of sunscreen creams was initiated, which in addition to pure UV protection also offer infrared protection. In this connection, premium manufacturers now often make the claim: “Without infrared protection, you are only half protected against the sun”.

If one compares the proportion of UV light striking the earth with the amount of infrared in the sun’s radiation, the question inevitably arises as to why this topic was not addressed much earlier. There seems to be no point in unnecessarily exposing one’s eyes to heat radiation.

UV-light diagram

Amounts of UV light and infrared light striking the earth due to solar radiation.

According to the findings of the Association for Radiation Protection, wavelengths of light between 780 and 10,000 nm can cause significant thermal damage to the eye. It is important here to make a distinction between work safety protection and sun protection, because the spectrum of sunlight hitting the earth is completely different from that e.g. when working in front of a blast furnace. Thus the relevant area of ​​consideration in this context is the frequency range up to 2,500 nm.

Radiation intensity diagram.

Radiation intensity diagram.

Depth of penetration: What impinges where on the eye?

A significant proportion of the dominant infrared (IR)-A component in sunlight in the range up to 1,400 nm penetrates to the retina. This follows the general rule: the shorter the wavelength of the IR radiation, the greater the depth of penetration. This particularly affects the choroid which can be damaged by IR-A, leading to localized defects in the retina tissue. Only a small proportion of radiation with wavelengths longer than 2,000 nm gets through the cornea. The anterior chamber of the eye absorbs all radiation above 2,000 nm. All wavelengths greater than 1400 nm are filtered out by the lens and vitreous part of the eye.

Spectral transmittance

Spectral transmittance.

Significant radiation in the wavelength range of 400 to 1400 nm can fall on the retina. The infrared radiation energy that the eye absorbs causes it to warm up (Vos and Norren 2004, Brose et al. 2005). The exact mechanism by which long-term exposure to IR radiation leads to clouding of the eye lens (cataract) is still not fully understood (Brose et al. 2005). It is also difficult to distinguish between the fundamentally multifactorial-related development of cataracts and numerous other biochemical changes – in particular changes in the composition of lens proteins with increasing aggregation of insoluble high-molecular proteins – and cellular changes that are genetically modified and are affected and exacerbated by environmental factors (Truscott and Zhu, Michael and Bron 2012).

Not for nothing are certain kinds of cataract referred to as fire cataracts or glassblowers’ cataracts. The effect of infrared radiation on such a condition is difficult to prove due to its development over a very long period and thus it is difficult to setup a test, but it is considered very likely.


A general distinction must be made between the front and rear parts of the eye. Where protection of the lens with regard to sun protection is concerned, the infrared spectrum from 780 to 2,500 nm is of interest​​, whereby the anterior chamber of the eye already offers fairly good protection between 1,300 and 1,500 and above 2000 nm.

Thus the main stress on the lens is in the ranges 780 to 1,400 nm and 1,500 to 2,000 nm. Up to 1,400 nm, IR radiation penetrates to the retina, causing it to warm up.

The well-known reasoning that a reduction in the transmission of visible light (e.g. through standard sun protection of 85%) leads the eye to adapt to the light conditions, thus in the case of lenses without UV protection letting in more UV radiation than untinted lenses, can be transferred 1: 1 to the infrared problem. In other words: wearers of sunglasses without infrared protection expose their eyes to more IR radiation than if they were not wearing sunglasses at all.

As a consequence of increased life expectancy, no opportunity should be missed to limit potentially harmful external influences – particularly on the retina – to an absolute minimum. Ultimately, this is exactly what we have been doing in our industry with regard to UV protection for decades.

Transmission change simulation

Simulation of the effect on the transmission change on the respective medium – black without the coating / red with IR coating.

An IR protection coating on sun protection products reducing the transmission between 780 and 2.000nm to a minimum for providing optimal protection to the lens and the retina is a useful step to differentiate professional sunglass protection products from discounter products by providing additional benefits

It is an added value that can be easily explained to the end user. Ideally, in time it should be recognized with a similar stamp of approval to UV400. Moreover, this additional protection would highlight the distinction between our products and those of the fashion sunglasses industry.





Historical grinding machine for spectacle lenses

Historical grinding machine for spectacle lenses

Image section from Diderot Lunetier 1

Mineral glass is difficult to work, especially the rock crystal beryl initially used to make spectacle lenses, because of its hardness. So anyone who wanted to turn a piece of glass into a visually effective lens needed a lot of patience and perseverance. Whether a lens could ultimately deliver a distortion-free image depended entirely on the precision with which it was worked. Thus it is not surprising that, in the late Middle Ages, methods were sought based on wind and water power to produce spectacle lenses with the required finish, if possible without the need for human labor. The advent of the industrial revolution two centuries ago with its motor-driven machines finally made it possible to manufacture spectacle lenses on a routine basis.

By Dr. Hans-Walter Roth

In the beginning grinding of spectacle lenses was done entirely by hand. Thus chroniclers report dozens of unqualified workers spending days giving the blanks supplied by the glassworks their desired shape. On grinding machines, whose antecedent was the potter’s wheel, one side of the lens was ground to a shape corresponding to a spherical surface. The other side was initially flat, as with lenses for reading placed on the page. Only later did lenses become biconvex. Provided the diameter and refractive index of the material were known, the strength of the spectacle lens could be calculated from the difference between the central thickness and the edge thickness. Prior to the introduction of the metric system two centuries ago when the diopter was introduced as a measure of spectacle lens strength, previously only the focal length was specified. It was easy to determine: you just had to hold the lens up to the sun and, by focusing the rays of light for example on a piece of paper, you could find the focal point. The oldest surviving pair of glasses was found in 1953 under the choir stalls in the nunnery at Wienhausen, founded in the 13th century. Like most glasses at that time, the strength of the lenses was +3.4 diopters, showing that they served as a reading aid to compensate for presbyopia.

The beginnings of automation

 With the invention of printing, the demand for reading glasses increased dramatically as more and more people learnt to read. The lengthy process of grinding by hand, however, prevented mass production of reading aids. Thus it became imperative to automate the lens-grinding process. As early as the 16th century, there had already been some quirky constructions to grind several lenses in series simultaneously.

Diderot’s encyclopedia, published in France from 1751, includes illustrations of various devices and tools used to make lenses for a variety of optical instruments, including spectacles. The grinding machine has a solid wooden frame similar in principle to that of a potter’s wheel. A large flywheel is driven by a hand-operated crank, with a leather drive belt transmitting the rotation to a small wheel, thus multiplying the speed of rotation by a factor of 1: 5. The precast biconvex glass lens is mounted in a concave support cup on a vertically mounted rotating rod. This in turn is connected via a wooden bevel gear to the small wheel in such a way that one turn of the hand crank makes the lens rotate five times about its own axis.

Above the lens holder there is a metal bar fixed with two wing nuts, to which various grinding and polishing heads can be attached. These are shown in the subsequent figures with different radii of curvature, showing that different lens thicknesses can be ground on the same machine. The concave polishing heads and the holders for the lenses are made of metal – usually brass – prefabricated on a lathe. A thin piece of leather between the lens and the holder prevents the surface of the lens from being scratched while it is being worked and held securely.

The illustrations shown here are from one of the numerous editions of the Diderot encyclopedia. They were purchased individually from one of the many booksellers on the banks of the Seine in Paris. Unfortunately, today there are hardly any complete editions of the famous encyclopedia from the 18th century on the market; savvy dealers preferring rather to separate them and sell the pages individually, in order to make more money.

Diderot Lunetier 1, Lenses from different sources.

Diderot Lunetier 1, Lenses from different sources.

Diderot Lunetier 2, Tools.

Diderot Lunetier 2, Tools.

Diderot Lunetier 3, Tools.

Diderot Lunetier 3, Tools.

Diderot Lunetier 4, Cutting and polishing machines.

Diderot Lunetier 4, Cutting and polishing machines.

All pictures in this article are courtesy of the Institute for Scientific Contact Optics Ulm.




The Craftsmanship of Ophthalmic Coatings

The Craftsmanship of Ophthalmic Coatings

Principal knowledge on procedures and best practise

The objectives of this article are to provide general principal knowledge on ophthalmic coating manufacture procedures and best practises based on a hands-on lifetime experience in coating manufacturing. Moreover, it is meant to draw attention to pitfalls and possible risks, to show shop-floor level staff how to apply themselves, to take ownership of the work and to enable suitable candidates to be an efficient coach in the lab. At the end of the day the quality level achieved in a coating department is determined by the quality of workmanship of the least trained staff. By Georg Mayer

The text is an extract of a tutorial held first at the Annual Society of Vacuum Coaters (SVC) Techcon 2019 in Long Beach and to be presented again in an updated version at this year’s SVC Techcon April 22nd in Chicago. I will focus on the next few pages on some highlights of the full day course tutorial.  In nearly 20 years of sole responsibility of the coating division of a then market leader, I gained some valuable lessons. Having had the privilege and pleasure to work with staff from 5 European and African Countries was an enriching and exciting experience.

Some ground rules for every case

Here are a few conclusions after working nearly 40 years in coating

  • Be a professional pessimist, expect the worst to happen and plan accordingly.
  • Don´t assume, ask! There are no stupid questions, only stupid mistakes.
  • Be a stickler to the rules of the process owner, don´t change anything, it is always better to ask again.
  • Consistency is the name of the game, more of that later …

You might ask yourself how can this experience still be of any interest today, in our increasingly automated Rx factories, gearing up for Industry 4.0?

Rx lens making is mostly automated – a computerised digital production with the ability to check and verify every lens to all standards applicable in situ. Rx surfacing runs in a continuous flow, job by job and can be driven by only a few staff with the help of advanced fully integrated lab management software.

By Elisabeth Mayer

However, when the Rx jobs arrive at the coating department´s door we seem to go back in time.

We interrupt the job flow for batching, not only once but often twice with related waiting times and sorting action per material/index and per coating type. Due to the unique shape and form of Rx lenses we still have too many hands on those lenses, all the way through the coating department. First they go from batching into carriers to cleaning to hardcoating and curing. And then again they go from batching and handling into different carriers for preparation and vacuum coating, typically twice with manual flipping and prep-steps in between.

In summary, we have multiple manual manipulations on lenses and machines, meaning a lot of staff are in direct control of the coating quality. And if those manual manipulations on lenses, machines or processes are performed in a country by operators with language barriers, training needs particular attention as those staff form a crucial part of a consistently good quality.


On top of all of this we don´t have the ability to check the full and final quality of each of our coatings produced without destroying it, we can only test samples or “witness” substrates which have taken part in the same process and batch.

Test yourself: what do you think is depicted in these pictures? You can find the solutions at the end of this article.







Keep an eye on sampling method, process and FPY

This leads directly to a first major subject, – the sampling method as a basis for coating quality metrics.

  • Sampling only works if all lenses are processed consistently to the rules of the process owner
  • Only then such witness samples will have the same properties as all other “real” Rx lenses

In conclusion, if processes and staff are not consistent the sampling approach is misleading.

A second important subject is the previously mentioned process and the lab taking ownership and responsibility. The following list gives an overview of the most important points that should be considered regarding the process:

  • Apply stable robust processes, manageable by the local infrastructure, machines and team.
  • The process must be well documented and the documentation has to be easily understandable and available to staff at their workplace.
  • Part and parcel of a stable process is strict maintenance of machines and use of the correct consumables since you can´t separate machine from process.
  • Well trained staff is essential, each of them could be the weak link in an otherwise strong team.
  • Create a work atmosphere that is open to continuous questions, learning and improvement, all the time.

Such stable and robust processes are the basis for a third most critical topic, the first pass yield (FPY) and its primary impact on an Rx lab’s ability to deliver consistently on time which leads to customer satisfaction.

A simplified example/case for this is based on the Markov Chain:

Of 100 lenses to enter a coating department, how many will come out “first round / first try” with its typical successive process steps? Let´s assume each main coating production steps FPY being

Hard coat                          96%

First side AR                      99%

Second side AR                 99%

Handling/washing            99%.

Looks pretty good, doesn´t it, but the key is that in combination the final score is a multiplication of 0,95×0,99×0,99×0,99=0,92 or 92%, meaning 8 of our 100 lenses didn´t make it first time round.

To make matters worse, in Rx where jobs are 2 lenses it could be double the number as a single bad lens in a job will hold back the other good lens too. So, this coating department could have a FPY as low as 84%, or in other words 16% of all work is not out first round in the expected time.

Once the whole Rx lab’s various factors have been modelled the results can be used for the prediction of the customer’s perception of this lab, i.e. if customers’ expectations will be met.

The main delivery quality indicators are delivery speed, reliability and consistency.

Such a lab might be competitive fast with the jobs making it on first attempt (84% FPY), but with a significant 16% of work not on time the lab will be seen as unreliable, and worse, of those 16% another 2% will not make it through even the second time and will need a third round. And because of this noticeable tail of very late work the lab is also regarded as not consistent.

Conclusion and brief outlook

Rx labs coating management must focus all efforts to achieve and maintain the highest possible yield rate for each type of product made by the lab, based on stable processes and well-trained staff, because of its primary impact on delivery quality and customer satisfaction.

Once this goal is achieved the focus can shift to removing the remaining major system shortfalls in most coating departments, i.e. to the improvement of the degree of automation and the reduction of the process times while still maintaining expected market quality standards for Rx lenses.

We can foresee some exciting new developments and projects in that direction, partly already in use or still to come, which will change the landscape of Rx lens coating to bring it closer to the level of automation seen already in Rx surfacing.

Solution for pictures a) to d):

a) Hardcoating failure
b) AR stack thermal cracking
c) Hardcoating striae
d) Droplet spitmark residue under AR


Sustainability in ophthalmic optics

Sustainability in ophthalmic optics

glass ball with continents on forest floor

Sustainability in ophthalmology, what does that mean for our industry? Can we withdraw from the current debate about ecology and climate protection? Can we just ignore these topics? Undeniably, we are subject to physical-chemical laws in the manufacture and disposal of ophthalmic optical products. And supply and aftercare industries will carry on trade economically, simply out of self-interest. But do we have to tolerate unconditionally the poor working conditions in low-wage countries? Do we have any influence on business ethics there? The reputation of our industry will benefit if we discuss these environmental issues openly and look for solutions.

By Johannes Schweinem

The term ‘sustainability’ was originally coined by Hans-Carl von Carlowitz, when clearing forests to provide fuel and building materials. Around the year 1700, when neither natural gas nor oil were yet used as fuel nor concrete in the construction industry, wood was under threat because of short supply. Then coal mining took off with the advent of industrialization and the term ‘sustainability’ disappeared from view – especially as there seemed to be no limit to the supply of coal. Later, as the steam engine was supplanted by the internal combustion engine, hydrocarbons came on the scene which, as everybody knows, were – and still are – derived from oil. By 1960, there was a policy of ‘unrestrained economic growth’ and the throwaway society reached its pinnacle. The discovery of the ozone hole in 1980 and the decimation of forests in 1985 – to name just two key issues – made society aware of environmental issues. In 1990 discussions about recycling were instigated for the first time.

Cornerstones of environmental policy

In Germany, the Recycling Management Act was passed in 1996. The ‘green dot’ and the ‘yellow recycling bin’ are direct consequences of this law[1]. Research based on drilling ice cores, which took place at roughly the same time, and the insights this gave into events over the last 150,000 years, provided the final proof of anthropogenic climate change. In 1997, the Kyoto Protocol was drafted, which was subsequently adopted as the United Nations Framework Convention on Climate Change. Sustainability became an international obligation which today is integrated into the three-pillar model:

  • Environmental sustainability,
  • Economic sustainability,
  • Societal sustainability.

Environmental sustainability calls for examination of our ‘ecological footprint’. This is the natural area that is necessary to permanently enable a person’s standard of living and lifestyle under current production conditions. This includes the production of clothing and food, the provision of energy for heating, work and leisure, as well as the disposal of pollutants (e.g. residual waste). The area of ​​the forest required to assimilate CO2 emissions is also included in this area (Fig. 1). Some Internet platforms offer an online calculator that allows people to calculate their own ecological footprint.

Diagram of “ecological footprint” of the world population in ha/head/year

Fig. 1: Size of the “ecological footprint” of the world population in ha/head/year (Source: Global Footprint Network, Brussels, 2014)

Economic sustainability concerns natural resources, how long certain raw materials will continue to be available before they are exhausted (Fig. 2) and how they can best be shared, so they continue to be available to future generations. This includes, in particular, the recycling of used materials and the secondary raw materials which can be derived from them, as well as increased efficiency in the production of new goods.

Metal extraction from primary raw materials (ores)/Plastics production from crude oil

Fig. 2: Metal extraction from primary raw materials (ores)/Plastics production from crude oil (Metal extraction from primary raw materials (ores)/Plastics production from crude oil)

Societal sustainability identifies and corrects the even distribution of the ‘footprint size’ across all nations. Ethical responsibility with regard to other cultures is just as important as the solidarity of all people with regard to public health. Europeans today want to know how our jeans are made in Bangladesh and under what conditions people in Far Eastern factories work for us. Exploitation is today largely rejected by a majority of the population. It is not always the cheapest which is best, where sustainability is concerned.

Spectacles – still the core business of ophthalmic optics

Spectacles are likely to remain the core business of ophthalmic optics for the foreseeable future. Besides good quality – perhaps the key attribute of a reputable local optometrist – the question of sustainability is becoming increasingly important. Not only do the materials used need to be biodegradable – this could be considered a shortcoming in daily use –it is also important under what conditions the lenses and frames were made. Is health protection assured for everyone involved in the production process? Are ecological and economic consider­ations compatible with the production process? Are the spectacles ultimately recyclable?

For an example, we should consider a pair of spectacles where the lenses are made of plastic with a standard refractive index of 1.6, the rims are made of Monel and the sides made of stainless steel. One can assume that the side tips are covered with cellulose acetate. The replacement rate for spectacles today is about four years. How, then, do the three pillars of sustainability impact on these spectacles – from manufacture to disposal?

Lenses made of plastic…

The monomers for the lenses are produced by a branch of the Japanese petrochemical industry and supplied in drums. Monomer 1 is a tetravalent molecule that reacts with terminal mercaptans. Mercaptans are short, homologous hydrocarbon chains with a terminal hydrogen sulfide grouping. The tetravalency affects the subsequent thermosetting of the finished lens. Monomer 2 is a di-isocyanate, i.e. a bivalent, reactive nitrogen-carbon-oxygen compound with a cyclic nucleus. From an ecological point of view, the chemical production of the monomers involves several intermediate stages requiring heat and releasing CO2 during the heating process. The chemical manufacturing technology in Japan as well as the occupational health and safety standards there are comparable to those in Europe.

… when casting the monomers…

In the further course of production, the monomers are supplied to those carrying out the casting in separate containers. The two monomers are poured together there into molds to make the blanks. Here, however, there are significant differences with regard to social and societal sustainability. On the one hand there are the castings manufactured under European safety standards, while on the other hand there are cheaper blanks from the Far East, manufactured without adequate health and safety protection often by underpaid employees, which are supplied to Europe.

Both the professional associations such as the Federal Institute for Occupational Safety and Health (BAuA) monitor that the workplace regulations specified in the German standards – also known as MAK values ​​– are complied with in production. Just as any liquid can evaporate before it reaches its boiling point, i.e. takes vapor form, so too can monomers release toxic molecules into the surrounding atmosphere. The more toxic the volatile substances are, the lower the MAK values ​​ set by law. Monomer 1 is classified as “toxic”, monomer 2 as “very toxic”. The MAK value of the di-isocyanates is 0.005 ppm (parts per million) in ambient air, which may not be exceeded over an 8-hour working day. In Germany, the casting process takes place in isolated areas. In China – as a connoisseur of the Chinese casting market for optical products has reported – the two liquid monomers sometimes run directly over the employees’ hands. Here, it is right to ask whether social and societal sustainability is genuinely assured – even if business ethics are being taken increasingly seriously in China.

… and during edging

The smell of rotten eggs which arises in German opticians’ labs during edging is caused by hydrogen sulfide being given off. After all, 1.6 index plastic lenses contain 20% of sulfur, which originally stem from the mercaptans in the monomers. Although hydrogen sulfide is also toxic, the mucous membranes of our nose are so sensitive to the smell that irritation occurs long before a dangerous concentration of toxins can build up.

A study in 2004 by the Higher Professional School for Ophthalmic Optics in Cologne (HFAK) together with then professional association BGFE showed experimentally that even in the worst-case of grinding 42 high-index plastic lenses per hour in a closed room (without ventilation) only 1.0 ppm of hydrogen sulfide was emitted. The MAK value of hydrogen sulfide today is 5 ppm. So this effectively gives the all-clear for toxins in German grinding labs.

The middle part made of Monel…

Monel has long been a common material used for the bridge of a pair of spectacles (Fig. 3). A similar alloy (nickel-silver) is used to make closing blocks, bridge and joint parts. The metals nickel, copper and zinc, mainly used in the alloys, only need be present as pure metal in small amounts. Thus the largest proportion of the nickel-based alloy Monel and the copper-based alloy nickel-silver are produced from charges of scrap metal (Fig. 4). During charging, high demands are made on the reproducibility of alloys, whereby – by presorting scrap by alloy composition and precise doses of scrap master alloys as melt addition – only a small proportion of pure metals from primary raw material sources (ores) are needed for fine adjustment. The method of scrap charging has the economic advantage that the process only needs to heat the charge to the melting point of the metal alloys, and the heat which otherwise would be needed to melt the ores – which may be four times as high – is not required. In ecological terms, too, this means that the reserves of ores can be saved in this way. In 2014, the European Copper Institute (ECI) in Brussels declared that the known reserves of copper from primary sources will have dried up in about 50 years. Consequently, the ECI is promoting the use of copper alloys from secondary sources (Fig. 5).

Process of alloy-metal recovery from secondary raw materials

Fig. 3: Process of alloy-metal recovery from secondary raw materials (*Pure metals from primary sources are essential to obtain the required composition of the alloys)


Metal extraction from secondary raw materials. Increase in the amount of recycling over the past 5 years.

Fig. 4: Metal extraction from secondary raw materials. Increase in the amount of recycling over the past 5 years. (Sources: Federal Institute of Geosciences, German Raw Materials Agency, Economic Association for Non-Ferrous Metals, ECI, Steel Industry, Remondis Recycling)


Non-toxicity of polyurethane

Fig. 5


… and sides made of stainless steel

The same applies to spectacle sides, which in our model are made of stainless steel. The traditional coal and steel industry, i.e. the historic production of steel from the reduction of iron ore using coal in a conventional blast furnace, is no longer absolutely necessary today and has largely been replaced by electric-arc furnaces melting recycled steel scrap. The stainless steels used for spectacle frames are mainly ferritic steels made of alloy steel and chrome. Again, here too, the production of crude steel has largely been replaced by alloys.

Over the wearing life of our model spectacles – in our example four years – no di-isocyanate was given off by the glasses (Fig. 6). The finished blanks are non-toxic because the substituents of the monomers (here mercaptans) are poly-added with the isocyanates. Polyurethanes consist of the chemically stable urethane moiety within the macromolecules. Plastic lenses comply with European standards without compromise, in accordance with CE conformity and the German Medical Devices Act. Likewise, the nickel content of the spectacle frame is protected by proven coating processes.

Treatment plant for residual waste.

Fig. 6: Treatment plant for residual waste.

The end of a pair of glasses…

What happens to our spectacles after four years at the end of their life? It certainly makes sense to collect old pairs of spectacles and give them to the German Opticians’ Development Service or equivalent institutions in other countries. In Germany, the Association of Opticians and Optometrists can also provide addresses of opticians who maintain contacts to Zimbabwe or Mali. Passing on technologies and goods to other countries may well be an ethical responsibility that should not be ignored.

From an ecological point of view, recycling also makes sense by ensuring that metal frames are given in large quantities to a scrap merchant, thus relieving the pressure on primary ore resources. Unfortunately, lenses made from plastic cannot be recycled because as thermosets they cannot be remelted. So what happens to them? And how do customers finally dispose of their old glasses? The legislation does not require the individual parts of the spectacles to be separated and often they simply end up in the residual waste. So let us now take a closer look at this final stage in the life of a pair of spectacles.

… into the incinerator

The content of a residual waste bin is transported by truck to a collecting area, from where it is taken by train to a large waste incineration plant. The Recycling Management Act of 1996 requires sorting of residual waste for recyclable materials; residual waste may no longer be dumped untreated into landfills. Waste incineration plants are now well established, ultimately leading to a reduction in the overall amount of waste. At these waste-disposal plants, the incoming waste is initially sorted on shakers using magnets (Fig. 7). As likely as not, the ferritic of the sides will be attracted to the magnets and thus the whole spectacle frame will be fished out. However, if the spectacles were first crushed in the trash – with the steel sides becoming separated – the central part of the spectacles may end up in the incinerator.

Cotton plants - the raw material for cellulose acetate.

Fig. 7: Cotton plants – the raw material for cellulose acetate.

On rotating grids, the burning garbage is constantly turned over. The plastic parts of the frame (side tips, nose pads and plastic lenses) burn mainly to carbon dioxide and water vapor. The cellulose acetate side tips account for about 45% by weight of the carbon-neutral CO2 which the cotton plants absorbed during growth (Fig. 8). More problematic are the lenses whose cyclic components of the plastic matrix in combination with chlorine from the overall waste can produce dioxins and furans.

The legislation specifies strict regulations concerning the retention of pollutants in waste incineration plants. Thus, the incineration chambers are designed in such a way that temperatures of up to 1200 °C occur above the flames, to ensure thermal decomposition of any dioxins or furans. The high temperatures, however, also have the side effect that nitrogen oxides are produced. Thus sulfur dioxide, sulfide residues and suspended particles are also left behind by our 1.6-index lenses. For this reason, filters are installed in waste incineration plants, such as suspended-particle scrubbers, hydrogen halide and sulfur dioxide separators, resin filters for heavy metal removal, ammonia catalytic crackers for the removal of nitrogen oxides and active carbon filters through which all gases have to pass before water vapor and carbon dioxide leaves the chimney. A little digression concerning plastic frames: it can be calculated stoichiometrically that a 12 g polyamide spectacle frame gives off 28 g CO2 during combustion.

Thermal recovery

From an economic point of view, when plastics are burnt, on average 60 % of the process heat required to produce the plastic is recovered as a combination of heat or power, and then returned to the grid as electrical energy. The remaining metal components of our model spectacles can also be recovered from the ashes and slag. They, too, can thus be returned to the metallurgists for use as a secondary raw material.

Polyethylene and polypropylene (plastic bags) burn with few emissions to H2O and CO2, whereby their calorific value is equivalent to heating oil (around 40,000 kJ/kg). If necessary, dirty packaging from the yellow recycling bin can be added, if the delivered residual waste mixture proves inefficient as a fuel.


Sustainability has now become a high priority. Today’s industrial practices are setting new economic-ecological standards. The questioning of the ethical production of cheap plastic lenses in part is up to us. We are all challenged to confront the key issues of the 21st century, to ensure that life for future generations remains worth living.

[1] All references to government or legislation in this article refer to Germany unless stated otherwise.

Ready for innovation in the eyewear industry?

Ready for innovation in the eyewear industry?


Innovation is the heartbeat of society. Big ideas for existing problems combined with the right technology results in innovative products with the power to revolutionize industries. The first industrial revolution resulted in tools, the second industrial revolution resulted in serial production and the third industrial revolution, 3D printing, will result in mass customization.

Across all industries, 3D printing has come to the forefront as a disruptor in creating completely new products and for more efficient manufacturing processes. It is now poised to offer a solution for frames and for custom lenses. The eyewear requires both customization and mass production, 3D printing fits seamlessly to fulfill those requirements.

By Guido Groet


Trends in society offer opportunities for the eyewear industry

If you zoom in on four main trends today that have a major impact on the eyewear industry:

  • The first trend is instant gratification, end-users want products immediate and without any compromises. To address this you see emerging platforms across the eyewear industry like online ordering platforms for sunglasses, websites to try out your glasses in a virtual environment or opportunities to measure your own prescription with a mobile device.
  • The second trend is customization of products, end-users prefer custom products over mass products. They want unique products tailored to their needs. This results in evolving distribution models to satisfy the end-user. For the eyewear industry, you see this emerging in custom 3D printed frames fully tailored to fit your face or 3D printed lenses customized for your eyes.
  • With technology evolving every single day, the third trend is that more products become smart. Why only correct vision through eyewear when the functionality of a phone or other devices could be added? Big tech players develop first generation smart glasses to enhance your regular glasses with functionality. Glasses have been passive devices for decades but with integration of technology your glasses will become active. The end-user will have one single product with multiple functionalities and might not need a phone at all.
  • The final trend is sustainability, end-users take into account the burden manufacturing processes and products have on the environment. The world will be focused on reduction of waste, energy and reducing the carbon footprint of product manufacturing. Also elimination of toxic components will be the norm. With 3D printing, you can provide a more sustainable alternative compared to traditional manufacturing as you add material.

The impact of 3D printing for the eyewear industry

3D printing has the most impact where there is a need for volume, and individual customization, which is exactly what the eyewear industry requires. The eyewear industry has found a way to address this need within the limitations of today’s legacy technology. With offering 3D printed lenses you will not require huge inventories, a complex supply chain or have a limited product design.

3D printing offers ophthalmic labs and eyewear companies an opportunity to maximize the industry’s potential and change aspects of the eyewear industry. This plays in satisfying the trend of instant gratification.

Focus on smart glasses

Let’s focus on the one trend where we see a strong contribution from 3D lens print technology: smart glasses. After the introduction of the first smart glasses several years ago, the adoption was not quite what technology companies anticipated. However, in today’s world people get more and more interested in adding multiple functionalities to their products.

The adoption of the smart phone is an example of adopting smart devices. But why stick to adding more devices in your day to day life while you can combine it into one single product? This paves the way for introducing real smart glasses.

Sixty percent of the population is not able to see without a prescription. Each lens must be customized for the wearer. The lenses cannot be simply picked from a shelf. Roughly 4.6 billion people require vision correction. In the developed world, greater than 84% have selected spectacle lenses as their primary vision solution. People need a good vision solution in smart glasses. Any smart glass solution will require addressing the prescription need, and this is where 3D printing can play a unique role.An AR/VR design which truly integrates prescription lenses would meet the visual needs for the majority of the population. A manufacturer which takes this approach would gain a cosmetic and functional advantage over competitors who are offering bulky, heavy, unattractive products which attempt to fit over regular prescription eyewear. Providing the best wearer experience using an amazing new 3D print technology might be what is needed.

What eyewear experts considered impossible is now possible; transparent and high-quality 3D printed prescription lenses. We are the first in this space and our 3D printing technology is installed commercially, printing prescription ophthalmic lenses daily, for shipment to end users. We understand the complexities of ophthalmic lenses and are poised to work in partnership with the AR/VR industry.

Bulky glasses

Most of the AR/VR glasses available today look bulky and uncomfortable and people even feel silly wearing them. By truly integrating prescription lenses into smart glasses design, manufacturers have an opportunity to disrupt the industry of mostly bulky, heavy and unattractive products. Some companies have made steps to provide prescription inserts which can work but could be significantly improved and be truly part of the design.

When manufacturers treat prescription lenses as a “must have” element instead of an afterthought, this will open many opportunities for AR/VR sales and positively influence buyer adoption.

Prescription lenses for technology companies

Technology companies often have a limited understanding of the complexity of delivering prescription lenses to end users. Prescription lenses are medical devices, with regulatory requirements. Many technology companies have a business model which stocks products until a consumer places an order and they ship the product to the consumer. Once vision correction is required, this model will not work.

To stock just the most common lens prescriptions would result in more than 3 million SKU’s (Stock Keeping Units). Luxexcel technology offers a turnkey solution without massive capital investment. In the long term point-of-purchase printing is possible so when you buy your smart glasses you can get your prescription added right in the store.Offering an immediate solution to the customer demand.At the moment 3D printing of lenses is deployed in the eyewear market, commercially shipping lenses daily to consumers through customer labs. In parallel, we are providing prescription lens inserts to several companies in the AR/VR space. We have not yet rolled out the technology to fully integrate 3D printed lenses where we print on top of the smart technology.

Is the eyewear industry ready for a sustainable future?

Soon our world will be populated by more than 10B people. We collectively generate an impressive amount of waste. It is clear that also the eyewear industry will need to make its own contribution and work towards reducing the impact on the environment.

Today this is clearly not happening enough with legacy technology. 3D printing is a technology that can help reduce the carbon footprint and the amount of waste generated, for our industry.

Is the eyewear industry ready for a smart future?

Several of the four main trends are addressed by eyewear companies. New innovations emerge every single day like custom 3D printed frames, measurement devices for your own home and new AR/VR glasses.

However, 3D printing opens up real possibilities for ophthalmic labs and technology companies to make custom products with added value. Examples are lenses with a screen or reflective device inside.

We have made prototypes in which we print on top of the electronic device creating an integrated visual solution. What it does for the end-product is to combine smart and functional eyewear with an acceptable and fashionable appearance. The eyewear industry is ready for the next innovation, but are you?


Guido Groet is Chief Commercial Officer at Luxexcel. He has an extensive background in technology and has been instrumental in bringing new technologies to market. Having worked for many years in both Europe and the USA for technology giant ASML world leader in semiconductor equipment. He has held VP positions in Business development, M&A, and Strategy development and has been in charge of the business relationship with key optics partner Zeiss in Germany. He has also been COO and subsequently, CEO of a venture capital financed company in disruptive high tech manufacturing technologies. At Luxexcel Guido is in charge of all commercial aspects of the business.