With surgery still being in its infancy, glasses are still the most realistic option for many patients. But they suffer from a major drawback: they make it difficult for your eye to focus at different distances, which can be dangerous, especially in the workplace. This is where the EU-funded LIGHTSWORDS (Lens that mIGHT be a Satisfactory Way Of Reducing age Degradation of Sight) project comes into play, with the promise of a plastic lens allowing for continuous focal adjustment from near-field objects to… infinity.
LIGHTSWORDS is following up on theoretical research that emerged 20 years ago. At the time, the concept of a lens eliminating the need for mechanical focus adjustment had emerged but technology wasn’t mature enough to bring this concept from lab to market. The LIGHTSWORDS project has solved this problem with a set of embossing and injecting technologies and a game-changing lens capable of continuously varying optic power from 0D to about 3D — making it possible to recognise objects placed at distances of about 33 cm to infinity with a good level of image sharpness.
Krzysztof Grabowiecki, coordinator of the project, tells us about its results and his plans for further developing the LIGHTSWORDS technology.
What are the main objectives of this project?
Our objective is to develop the necessary technology for production of a novel optic structure called Lightswords and to have it ready for production. This technology relies on an asymmetric optic structure. This means that the lenses are embedded with extended depth of focus, which could replace zonules of Zinn with crystalline lens for adapting vision to specific needs.
These mechanisms are key to solving problems faced by patients affected by presbyopia. With a single lens, they will be able to observe objects from various distances without a meaningful loss of sharpness, although the result will be slightly below that of regular single focus lenses over long distances.
The theory behind the LIGHTSWORDS technology was developed some 20 years ago, but there were no physical applications due to difficulties with lens manufacturing: small curvature continuously varying around the axis and small, sharp steps. Our task was to find the proper technology, which would satisfy at least the theoretical constraints related to manufacturing, and to start up a pilot mass production line.
You tested three different technologies. Did one of them stand out? How?
Three technologies (or four, when counting combinations) were indeed used for investigations on possible production of the LIGHTSWORDS lenses: regular micromachining of a single lens which is often used in industrial practice; micromachining with the possible application of EDM for mould die manufacturing (injection technology); laser lithography technology for mould stamp manufacturing (hot embossing technology); and micromachining for mould stamp manufacturing (hot embossing technology).
Finally, micromachining for mould stamp manufacturing was recognised as the best solution. A mould insert with the required precision was manufactured by the consortium and a first injection test batch of lenses was produced and characterised successfully. For optic characterisation, the test bench was set up to simulate human eye vision. Four objects were placed at different distances (0.33 m to 3 m) from the ‘artificial presbyopic eye’ which is basically a lens focusing on a fixed distance. We observed the correction of vision that we had predicted originally in theory: instead of having a single sharp object and surrounded by out-of-focus objects, the artificial eye corrected with the LIGHTSWORDS lens was able to see all four objects with a satisfactory quality — but not optimal — sharpness.
What were the main difficulties you faced during the project and how did you resolve them?
The main challenge was to satisfy very narrow levels of tolerances (micron or even submicron) for manufacturing in order to achieve a certain level of smoothness, while still keeping the usual shape and roughness of a lens. In particular, exploiting grey-scale laser lithography for thick photoresist was no easy task. The technology for thick/deep photoresist is not mature enough so our success was only partial in this regard. We were eventually forced to move to a ‘semi-refractive’ design of the optic structure. Finally, we focused our efforts on the micromachining and successfully reached our objectives.
How do your plastic lenses differ from other lenses currently available on the market?
The main thing is that, with our single lens, someone observing a scene can benefit from an extended depth of field. Our primary design relies on optic power 0-3D, which means that the depth of field extends from 33 cm (regular reading distance) to infinity. Present correction concept uses a number of optic structures: bifocal, pinhole, aspheric. However most of them request eye axis movements while, in the case of LSOE, the vision axis remain unchanged.
The project ends this month. Does the technology you developed meet your initial expectations?
In principle yes: we have technology ready for pilot production. We are also developing a dedicated testing setup is developed to assess the geometry and optic features of the lenses.
Do you have any follow-up plans?
Yes we do. Now that we have developed a real lens, which may be evaluated by ophthalmologists in clinics and tested by researchers focusing on the brain acquisition of image, experts also expressed interest in contact lenses and intraocular ones. However, novel materials have to be used to take on these challenges.
In parallel, we would like to develop certain CCD camera solutions for free of focus operations including embedded distance metering (rangefinder) and difficult lighting conditions. That would require sophisticated software development and hardware configuration for real time scene imaging, and such development is ongoing. We will start working on designs for protective goggles where our lenses will be incorporated, and obviously we will attempt to secure new EC funds for these purposes.
What do you foresee in terms of market impact? Have some lens manufacturers shown interest in mass-producing your lenses yet?
The impact on the market could be large due to the device’s low price and the high functionality embedded in the lens structure. Even more impact could be expected when contact lenses or intraocular lenses are considered; although we still need to wait for clinical results, including restrictions related to certain malfunctions of the human eye. We also see potential in a so-called machine vision solution for better and faster image acquisition or 3D scene analysis. Things like night vision and spectral evaluation of the observed scene could also be considered as the diffractive features of the asymmetric lens are exploited.
We have indeed witnessed some interest from some of the main players on the ophthalmic and camera development markets. However, it is too soon to disclose more information.