New retinal implant gives sight to nine blind people

1500 pixels, with no camera required; patients able to read letters
February 22, 2013

Subretinal implant (credit: K. Stingl et al./Proc. Royal Soc. B)

German and Hungarian researchers have brought sight to nine blind patients with hereditary retinal degeneration, using a subretinally implanted microelectronic chip with 1500 pixels.

The chip size is approximately 3mm x 3mm and is surgically implanted below the fovea (area of sharpest vision in the retina).

It provides a diamond-shaped visual field of 15 degrees diagonally across chip corners.

It is powered by a subdermal coil behind the ear that is powered from a battery via transdermal inductive transmission.

The microelectronic chip has 1,500 independent microphotodiode-amplifier electrode elements.

The core of the implant is a microchip with 1,500 pixels, each 70 x 70 microns. Photocells, an amplifying circuit, and a stimulation electrode are attached to each pixel. The photocells absorb the light entering the eye, transforming it into electrical signals. A tiny power line provides energy from the subdermal coil  Sixteen additional electrodes are placed for testing purposes at the tip of the implant

Microchip array (credit: K. Stingl et al./Proc. Royal Soc. B)

The incoming light intensity controls the amount of current released by each electrode, stimulating the neighboring intact retinal nerve cells electrically. The nerve impulses generated by the retinal cells are processed in the remaining neuronal network of the retina and transmitted via the optic nerve to the visual cortex, creating visual sensations. An unimpaired, regularly functioning optic nerve is required.

3mm x 3mm microchip is subretinally implanted beneath the fovea (credit: K. Stingl et al./Proc. Royal Soc. B)

The image entering the eye is picked up by subretinal photoreceptors in the fovea. (Credit: K. Stingl et al./Proc. Royal Soc. B)

“So far, our approach using subretinal electronic implants is the only one that has successfully mediated images in a trial with freely moving blind persons by means of a light sensor array that moves with the eye,” the scientists said.

“All the other current approaches require an extraocular camera that does not link image capture to eye movements, which, therefore, does not allow the utilization of microsaccades for refreshing the perceived images.”

In most hereditary retinal diseases, such as retinitis pigmentosa, the photoreceptors progressively degenerate, often causing blindness in adult life, and there is no therapy available to treat this disease.

UPDATE Feb. 23, 2013 — Additional description of microchip array added.

Letter recognition. A marker pen was used to write white letters on a black cardboard. The letters MIKA were written with a height of about 8 cm, and placed on the table in front of the patient. He recognized the name and identified the wrong spelling, as his name is MIIKKA, while the former Formula 1 driver Hkkinen, as mentioned by the patient, is written MIKA. Due to his small visual field he needed some time to first identify the number of letters and their location. For this task he needed about 2 minutes; the movie starts with the last minute of the searching process.

Presentation of 5 different letters. The letters I,L,O,T, and V were presented singly to the patient by sequentially activating electrodes with single pulses, using fixed voltage increments above the previously determined threshold. Pulse durations were 4 to 7 ms, with 208 ms between the activation of two electrodes. The sequence was shown only once per run. After one letter, a period up to 45 s was provided for the patient to give his answer, and for the bioengineer on the left (not shown in the movie) to set up the next letter, indicated silently by the investigator. The letters combine to the word “VOLT”, correctly named by the patient but never presented previously to him.