Hand-held device simulates cataract replacement

30 Aug 2016

CSIC project allows the effects of artificial lenses to be tested before surgery.

Cataract surgery and the replacement of the eye's natural lens with an unclouded synthetic substitute already makes use of sophisticated photonics technology, in the form of femtosecond laser sources for the crucial incisions, along with research into new optical diagnosis and treatment methods.

A team at the Spanish National Research Council (CSIC) has now developed a portable device able to simulate the multi-focal visual corrections that a synthetic intraocular lens (IOL) can provide to a patient, helping them to appreciate what the surgery might offer. The work was published in Optica.

An increasingly attractive solution for presbyopia - the loss of focusing power in the eye which comes to most with advancing years, if not before - is multi-focal lenses using diffractive or refractive profiles, resulting in bifocal, trifocal, and extended-depth-of-focus designs.

But it can currently be difficult for patients to imagine the new visual experience provided by some of these advanced synthetic lenses, making it hard for them to decide on the best one to have or for clinicians to be fully confident of the outcome.

The new hand-held device from CSIC, christened SimVis, could help. It is based on temporal multiplexing of an electronically tunable lens, and should prove a useful way to study visual performance with multi-focal corrections and select the lens design best suited for each patient.

"There are many different intraocular lenses in the market, which provide different balances of near and far vision," said CSIC researcher Aiswaryah Radhakrishan. "We have discovered a way to simulate these intraocular lenses and demonstrated a prototype device that allows patients to test different solutions before surgery, and choose the one that best suits their needs."

Tunable vision correction
SimVis can simulate the effect of a complex multi-focal IOL by altering the shape of the tunable lens so as to switch its focal position faster than the user can perceive. A patient looking through the device sees near and far distances in focus at the same time, as well as becoming aware of the differences in image quality and contrast that comes with multi-focal lenses.

In the Optica paper, the team describe as an example how SimVis simulated a 70-percent far and 30-percent near bifocal lens by inducing the two relevant optical states in a 20 millseconds time period, with the far state induced for 14 milliseconds and the near state for six milliseconds - effectively pure simultaneous vision, from the patient's perspective.

Future steps could include addressing how the technique simulates both the effects of specialized diffractive IOLs and the exact spatial distributions of the refractive lens designs, both of which SimVis does not currently do to a high standard. Incorporating phase plates or light modulators into the design could help tackle these issues, noted the project team.

And at present SimVis is a monocular instrument, so one obvious avenue of research is the development of a binocular version, by replicating a second channel for the other eye.

"Such a system could simulate not only monocular multi-focal corrections but also other presbyopia correction alternatives such as monovision and extended monovision, which involve different corrections in each eye," said the team in the Optica paper.