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The creation of a bionic eye that mimics the widening and shrinking of the pupil may bring us one step closer towards helping people with certain visual impairments.

Light enters the eye via the pupil, before travelling to the retina at the back of the eyeball. The retina then converts the light stimuli into nerve impulses, which are sent to the brain for processing via the optic nerve.

The so-called pupillary light reflex compensates for changes in light levels by adjusting the pupil’s size, allowing people to see in high resolution, while protecting the retina from bright light. This process can be impaired in people with an injury to their optic nerve or oculomotor nerve, which regulates eye muscle movement, resulting in double vision, light sensitivity or difficulty focusing on nearby objects.

at Nankai University in China and his colleagues have now developed a material that mimics the pupillary light reflex in an artificial eye model.

If humans ever want to use bionic eyes, this reflex has to be recreated, says Xu.

The material is based on the mineral perovskite, which is known to act as an artificial synapse. A synapse is the gap between two neurons through which nerve signals are transmitted, allowing the cells to communicate.

In a laboratory experiment, Xu’s team added the 625-nanometre-thick material and an alloy fibre to an artificial eye. When exposed to light, the material sent neural-like signals to the fibre, which then controlled the dilation and contraction of the eye’s pupil.

“It works in all light conditions,” says Xu.

The next step is to develop an artificial eye that perceives colour, says Xu. “Human eyes can recognise millions of colours and decode them at high resolution,” he says. “We plan to integrate this function in our artificial eye in the future.”

at the University of Manchester in the UK says an artificial eye with a pupillary light reflex could be useful.

“Any artificial eye would have to deal with the problem of resolving patterns in which differences in local light intensity may differ by only a few per cent against a billion-fold variation in overall scene brightness between starlight and daylight,” he says.

“A light-responsive pupil could be one way to address that problem, as it would act to keep the total amount of light reaching the light-detecting surface more stable.”