How Artificial Vision Can Restore Sight

Even with glasses on, you likely have enough vision to recognize the small text on this page. Most text on computer screens is roughly 3 millimeters tall and 2 mm wide (.12 x .08 inches). As you read this, you’re unaware of the countless pieces of visual data your eyes are processing every second. In the retina alone, millions of cells act as photoreceptors, responding to light much like a camera captures images on film.

The retina is a delicate layer of neural tissue that covers the inside back of the eye. Some cells are responsible for receiving light, while others interpret and transmit the information to the brain via the optic nerve. This process enables vision. When the retina is damaged or its photoreceptors stop functioning, blindness results. Retinal diseases affect over 10 million people globally, leading to severe vision loss.

For those who have lost vision due to retinal diseases, hope was once scarce. However, breakthroughs in technology are offering a new possibility: the return of sight. Several scientific teams have developed silicon microchips that can restore artificial vision. In this article, we will explore how the retina functions and why blindness caused by retinal disease doesn’t necessarily mean permanent vision loss.

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Understanding the Function of Your Retina

The eye is an incredibly complex and remarkable organ. To grasp how artificial vision is developed, it's crucial to understand the vital role the retina plays in your ability to see. Here’s a straightforward breakdown of the process when you focus on an object:

The retina, a delicate yet intricate membrane located at the rear of the eye, plays a crucial role in vision. Its primary function is to capture light and relay images to the brain. There are three key types of cells in the eye that assist in carrying out this vital task:

The retina contains approximately 125 million rods and cones, which serve as the photoreceptors for the eye. Rods are the more abundant of the two, outnumbering cones by a ratio of 18 to 1. They are sensitive to low light levels, capable of detecting even a single photon, and can create grayscale images in dim conditions. Cones, however, allow us to perceive color and fine details when there is sufficient light. These are the cells that enable you to read this text, as they provide high-resolution vision.

Press the play button to observe the effects of light interacting with the eye.

If the animation above isn't working, click here to download the Quicktime player.

The signals from the rods and cones are then passed on to the nearly one million ganglion cells within the retina. These ganglion cells process the data received from the rods and cones and transmit the information to the brain via the optic nerve.

Several retinal disorders target these cells, potentially leading to vision loss. Among the most prominent are retinitis pigmentosa and age-related macular degeneration. Both conditions damage the retina, disrupting the function of rods and cones and resulting in either peripheral vision loss or complete blindness. However, research has shown that these diseases do not affect the ganglion cells or the optic nerve. This suggests that if artificial rods and cones could be developed, the information could still reach the brain for processing.

Creating Artificial Sight

The development of artificial vision gained significant momentum in 1988 when Dr. Mark Humayun demonstrated that a blind person could perceive light by stimulating the nerve ganglia behind the retina with an electrical current. This experiment confirmed that the nerves behind the retina remain functional even after retinal degeneration. With this insight, scientists embarked on creating a device that could interpret images and convert them into electrical pulses, aiming to restore vision.

Currently, a device that could restore vision to millions of individuals who have lost their sight due to retinal diseases is on the verge of becoming available. The artificial silicon retina (ASR), created by Optobionics, was undergoing FDA clinical trials by the end of 2007. Over a two-year period, it showed improvements in the vision of 10 subjects [source: Groves]. However, by late 2007, Optobionics faced bankruptcy and was awaiting acquisition, which would allow the trials to continue.

As shown in the image at the top of this page, the ASR is an incredibly tiny device, even smaller than the surface of a pencil eraser. Its diameter is just 2 mm (.078 inch), and it is thinner than a human hair. This miniature size is essential. For the artificial retina to function, it must be compact enough for doctors to transplant it into the eye without damaging the surrounding structures.

A major breakthrough in artificial retina research came with the Department of Energy's establishment of the Artificial Retina Project, led by Mark Humayun. The ARP is a collaborative effort among public and private companies, universities, and research labs, all working together to develop a nano-sized device. Since 2002, six blind volunteers have been fitted with the device, helping them to perceive light, dark, and large objects. Additionally, the ARP is testing two other devices.

How the Artificial Silicon Retina Works

The ASR is equipped with roughly 3,500 tiny solar cells that can transform light into electrical pulses, simulating the functions of cones and rods. When implanting this device, surgeons make three microscopic incisions, no wider than the diameter of a needle, in the eye's sclera. Through these incisions, they introduce a small tool that cuts and vacuums the gel in the eye, replacing it with saline. They then create a precise hole in the retina to inject fluid, which gently lifts a section of the retina and forms a small pocket in the subretinal space to place the device. Finally, the retina is resealed over the ASR.

All microchips require power, and what makes the ASR remarkable is that it draws all its power from the light entering the eye. As mentioned before, light is focused on the retina. Therefore, once the ASR is implanted behind the retina, it captures all of the light entering the eye, converting it into solar energy. This eliminates the need for any wires, batteries, or external power devices.

Currently in development, a microchip designed to restore partial vision is being worked on by a team from Johns Hopkins University, North Carolina State University, and the University of North Carolina-Chapel Hill. Known as the artificial retina component chip (ARCC), this device shares similarities with the ASR. Both are made from silicon and are solar-powered. The ARCC, however, is a very small device, measuring just 2 mm square with a thickness of .02 mm (.00078 inch). Despite these similarities, there are notable differences between the two devices.

Unlike the ASR, which is placed within the layers of retinal tissue, the ARCC is positioned on top of the retina. Due to its minimal thickness, light entering the eye passes through the ARCC and strikes the photosensors on the back of the chip. However, the light does not provide power for the ARCC. Instead, a secondary device attached to a pair of eyeglasses directs a laser at the chip’s solar cells to supply the necessary power. This laser is powered by a small battery pack.

According to researchers, the ARCC will enable blind individuals to perceive 10 by 10 pixel images, roughly the size of a single letter on this page. However, they have indicated that they could eventually develop a version of the chip with a 250 by 250 pixel array, which could allow those who were once blind to read a newspaper.