BioPhotonics spoke with Bertrand Simon, senior lecturer at the Institut d’Optique Graduate School in France. He recently collaborated with SPIRAL SAS and Laurent Galinier on innovative lens design described in Optica. He spoke to us about spiral-shape lenses that provide clear vision at various distances, which could inform the enhancement of existing vision improvement technologies.

What are some of the limitations in current contact lens technology that you are aiming to address?

Achieving [extended depth of field] or multifocality can be of importance in ophthalmology, where these features ascend in importance for correcting presbyopia, especially when associated with other ocular conditions, as well as during the implantation of intraocular lenses after cataract extraction. However, the design of optics in ophthalmology is constrained by the size and wearability of contact lenses and intraocular implants. Multifocality is commonly achieved through diffractive or refractive designs, primarily based on modifications to the pupil through ring patterns. While effective, they can make the eye/lens system sensitive to the iris opening, causing potential issues, especially in photopic vision.

Indeed, we’re looking to resolve both the problem of multifocal loss in relation to illumination conditions — the eye’s iris opens and closes according to the amount of light. And the concentric structure of conventional refractive multifocal lenses means that not all focal lengths are present in high-light conditions, when the eye’s iris closes. The presence of halos or diffraction patterns may be observable in low-light conditions, in the case of diffractive multifocal lenses.

From a design standpoint, it appears that a freeform approach incorporating a spiral pattern was used to distribute the focal powers on the output diopter to improve image quality from multiple focal points. What instrumentation was required to accomplish this design?

We adopted a freeform design approach incorporating a spiral pattern to distribute focal powers at the lens output, thus improving image quality from different focal points. This process required the implementation of digital design tools, simulation tools, and precision equipment, such as digital lathes. These tools, combined with the use of computer-aided design (CAD) software and a specific numerical control, were essential to accurately sculpt the patterns and refine the design before manufacturing.

Have any contact lenses become available since you published your study? What aspects of your design have not yet reached the marketplace?

A series of lenses inspired by our research in Optica has already been released to the market through the LCS distributor, reaching regions such as France, Europe, Japan, the Emirates, Brazil, and Argentina. However, we are actively refining certain aspects, particularly our understanding of a lens’ behavior regarding eye aberrations, for which we have seen significant improvements in some wearer tests, and the optical vortices they generate. While the current products align with our initial concept, our methods have largely been empirical, relying on simulation tools. We are aiming to enhance the performance and the precision of the designs based on a stronger theoretical foundation.