Globally, nearly 50 million people are blind while another 34 million people are affected with severely impaired vision. Retinitis pigmentosa (hereditary disease that destroy photosensitive rod and cone cells in the retina) and macular degeneration (a condition that causes degeneration in the cells found in the centre of retina) are the leading cause of blindness in younger people. Although many developments in medical sciences have made treatments possible for vision correction, there have not been many breakthroughs when it comes to correcting blindness. However, researchers have developed an electrical prosthesis, bionic eyes, designed to partly restore sight for those suffering from partial or permanent vision loss.

Unlike prosthetics, bionic eyes are functional instead of cosmetic. Once implanted into a human eye, bionic eyes allow transduction of light, enabling people with vision issues to change light from the environment into impulses that the brain can process. Hence, the visual neuroprosthetic device could potentially provide useful vision and enhance the quality of life for profoundly blind people.

How does Bionic Eye Works?

The light-sensitive tissue layer found within the inner eye, known as retina, is responsible for transforming images from the outside world into neural impulses. These impulses are then passed along the optic nerve to thalamus and ultimately to visual processing centre of the brain. The bionic eye includes an external camera (mounted on a pair of eyeglasses), transmitter, and an internal microchip (surgically implanted into the retina). The camera serves to organize the visual stimuli of the environment before emitting high-frequency radio waves.

The microchip has an electrode array that functions as an electrical relay in place of degenerated retinal cells. The radio waves emitted by the external camera are received by the stimulator, which fires electrical impulses. The external video processor converts high-contrast image to electrical simulation parameters. Electrical stimulation of the surviving neurons leads the person to perceive small spots of light called phosphene. These phosphenes can be used by someone with bionic eyes to map out visual scene. The person’s brain then uses a series of flashing spots and interpret the environment-somewhat like a flashing mosaic.

Currently, the vision provided by a bionic eye is basic, providing wearer information about the location of an object, detecting a person, or finding a doorway. However, the future bionic eyes are expected to provide a high-resolution vision. Currently, only three types of retinal bionic eyes have been approved for commercial use.  

Argus II

The Argus II Retinal Prosthesis System is a three-part microscopic supercomputer that provides perception of light to patients with retinitis pigmentosa. Through surgery, a small electronic device is placed into the patient's retina, which helps them recognize shapes and patterns. Researchers have made progress in their recent studies of the Argus II using advanced computer model that enabled them to reproduce shapes and positions by arranging nerve cells in the eyes. Currently, team of developers is testing electrical stimulation waveform, which could enable the device to add colours and hue temperature to the mix.

Alpha-IMS

The Alpha IMS subretinal implant from Germany-based Retina Implant AG is first-of-its kind to be approved in the European Union. The 3X3 mm microchip is surgically implanted through trans choroidal approach under the foveal region to ensure retinotopically correct excitation. The subretinal implant has been composed of 1500 electrodes, which is significantly more than 60 electrodes in the Argus II. The greater number of electrodes allow light and dark images to appear more vibrant, which increase the visual resolution for the patient. The Alpha-IMS supports the natural movement of the eyes and does not require a camera or external component to capture and interpret images. With Alpha IMS subretinal implant, patients can see lines and gray scale, which the human brain interpret into meaningful images. Now, the researchers are focusing on enhancing the technical performance of the Alpha IMS.

IRIS II

Pixium Vision introduced IRIS II bionic vision system to people suffering from outer retinal degeneration. The 150-electrode epi-retinal implant is surgically positioned next to the eye. The camera embedded into a special pair of glasses converts electrical signals and transmits to the implant that stimulates nerve cells of the inner retina. The camera has independent pixels that continuously recognize changes. The system acts like the mass of a photoreceptor cells, which provide people basic vision capabilities. The IRIS II provides user with “useful selective visual perception”, mimicking the functioning of human by capturing changes in the visual scene.

Way Ahead

Bionic lenses could become the next big thing. They are designed to offer improvements in vision for those who wear contact lenses or eyeglasses. The surgeon removes a person’s natural lens and implant bionic lens to the muscles to restore vision at all distances. This helps the person to not experience any issues pertaining to the vision quality. The bionic lens technology autoregulates once it is implanted in the eyes. Since bionic lenses use 1/100 as much energy as natural lenses to respond, these lenses result in no risk of eye strain for the patient. Several companies are developing bionic lenses with different technologies and approaches, and soon these lenses are expected to change the quality of vision care. Compared to gene therapy, Argus II is less costly, but the vision is artificial. The gene therapy shows a promise in helping people regain vision without the use of implants as well.