The next generation of visual implants

There are almost 40 million blind people worldwide, with a further 124 million suffering from visual impairment. Researchers have long been looking for ways to at least partially restore sight to make everyday life easier for those affected. With the miniaturization of technology and improved data transmission and evaluation, visual implants are increasingly coming into focus.

Work on implant technology has been ongoing since the 1990s, with a focus on the miniaturization of components. At the cutting edge, around 1,000 electrons are currently used within. They can only do a fraction of what the millions of photoreceptors in the retina can perceive. Nevertheless, even low visual performance with the recognition of rough patterns, outlines and movements means significantly better quality of life for those affected.

Currently, the greatest progress in miniaturizing and improving the technology has been achieved by a group of researchers from Chalmers University of Technology in Sweden, the University of Freiburg and the Netherlands Institute for Neuroscience, who have succeeded in developing an electrode the size of a single neuron. The main problem, in this case the corrosion, was minimized by a unique mixture of materials, allowing the implants to remain in the body for a longer period.

The basis for the use of visual implants is the visual cortex in the brain. It also functions in blind people if part of the eye is damaged. It transmits information from the retina or from the electrons of the visual implants to the brain, where an image can be generated. The ultra-thin implant that has now been developed is only 40 micrometers wide and 10 micrometers thick, making it the size of a split hair. It is described as a thread with many electrodes arranged one behind the other. A visual implant would require several threads with thousands of electrodes.

A retinal chip is currently being tested to help with age-related macular degeneration (AMD). The retinal chip is implanted as a medium at the site of sharpest vision, reports Prof. Frank G. Holz, Director of the Eye Clinic at Bonn University Hospital. The chip captures light stimuli and converts them into electrical impulses like the natural retina. The visual information is projected onto the chip by an external camera, which converts the information into electrical impulses.

The special feature of this method is that the energy supply is provided by photovoltaics. This eliminates the need for a power supply cable. Patients learn how to use this chip through training after an implantation.

Another approach is to use visual prostheses that are implanted directly in the brain. The Utah Electrode Array (UEA) was developed at the John A. Moran Eye Center at the University of Utah. It is a cortical visual implant that can stimulate the neurons in the visual cortex. This creates so-called phosphenes: light perceptions that are not triggered by light but by other stimuli to the visual system, as when rubbing the eyes. These impulses are triggered using glasses with a mini video camera that converts visual signals into electrical signals. The visual experiences are rudimentary, but even recognizing people, doors or cars can increase the independence and safety of blind people.

Intraocular lenses, which are implanted into patients with cataracts or defective vision, do not require any electronics. They currently enable around 90 percent of those affected to live without glasses. The short procedure is generally painless and the lenses usually last a lifetime. There are several different types of lenses, depending on age and condition. The costs amount to several thousand euros.

Disadvantages of current solutions

What all current solutions with visual implants have in common is that the resolution is far removed from that of a healthy eye. Due to miniaturization and energy efficiency, visual information must be reduced to the essential data so that blind people can still understand it.

In future, deep learning methods should therefore be used to train artificial neural networks with images from everyday situations to extract only the most important visual information. This could leave simple phosphene patterns that are perceived in the brain.

While microtechnology already plays an important role in light perception and transmission to the brain in all work on visual implants, other solutions are increasingly coming into focus. A research team at the University of New South Wales (UNSW) in Australia has also miniaturized energy generation for visual implants and relocated it to the inside of the eye.

Just three of the smallest solar cells with gallium arsenide and gallium indium phosphide are sufficient to generate the voltage for signal transmission to the brain. Research is now being carried out into how these can be stacked efficiently to replace a wire connection in the eye.

Science Corporation's Photovoltaic Retinal Implant (PRIMA) is a wireless subretinal photovoltaic implant and consists of three main elements: a wireless subretinal implant, a pair of glasses with a camera and digital projector, and a wearable processor. The wireless prosthesis uses the function of photovoltaic pixels to convert projected light patterns into localized electrical current. The implant is a two millimeter wide, 30 micrometer thick chip with 378 pixels.