Looking ahead to an eye-tech future WIN-Initiative/Neleman/Getty

An artificial iris can open and close in response to sunlight without any other outside control, just like the ones in your eyes. This could help improve cameras and, eventually, repair damaged human eyes or control tiny robots that react to their surroundings.

In the eyes of humans and many other animals, the pupil is a hole that lets light inside the eyeball. The iris is the coloured part of your eye, a thin circle that controls the size of the pupil, modulating how much light gets through.

In bright light, the iris contracts to shrink the pupil, protecting the sensitive retina inside your eye, which sends visual signals to the brain. In the dark, the iris opens to let in more light so you can see. The same concept is used in cameras, which have an aperture that opens or closes to admit the right amount of light to create an image.


Such artificial apertures normally require an external sensor to tell them when to open or close. But now, Arri Priimägi at Tampere University of Technology in Finland and his colleagues have created one that opens and closes on its own.

To build their synthetic iris, they started with a thin disc 14 millimetres across, on which 12 radial petals were cut through the middle without reaching the edge – like a poorly sliced pizza. The disc is made of polymerised liquid crystal elastomer, a rubbery material that changes shape in response to heat.

When in the dark, each petal is bent and curled outward, leaving a round pupil-like hole in the middle. To make the iris respond to light like our eyes do, rather than to heat, the researchers added a red dye to their liquid-crystal mixture. When blue or green light hits the dye, it heats up, triggering the petals to curl back down and close the aperture.

“We shine light on the material and it changes its shape,” says Priimägi. “This self-regulation is new in this work and it’s what makes us excited about it.”

Pupil control

The team was motivated by the fact that artificial irises used now to treat humans with eye problems cannot change the size of the pupil – they are essentially just fixed contact lenses. With a set pupil size that is generally quite small and suited to bright sunlight, patients lose much of their sight in the dark.

Priimägi says the device is not quite ready to be implanted in a human eye because it doesn’t have precise enough control over aperture size and only responds to fairly strong light. “This is the first step – maybe we can go there one day,” he says.

“This is great, but applications will come down to the details,” says Jeremy Lerner, president of LightForm, Inc, a US imaging instrumentation company. “It depends on how fast it closes, how much light it lets through, and at what wavelengths.”

The artificial iris can close in seconds, but that will need to be sped up to the millisecond level for many applications, such as in sensitive cameras that could be ruined by suddenly pointing at a bright object. It may also need to close more tightly – at present, it still lets around 10 per cent of light through when fully shut.

But the researchers say these issues can be resolved. They hope the iris could eventually be used in microrobotics as sensors for tiny machines that can react to their surroundings.

“It’s an exciting case of a new world opening up with autonomous soft apertures driven by light in robots,” says Mark Warner at the University of Cambridge. “It’s a very nice piece of work.”

Journal reference: Advanced Materials, DOI: 10.1002/adma.201701814