Vision is arguably one of our most important senses. We rely on it to recognize color, shape, movement, distance, and perspective about the world around us. Although all parts of the eye help us perceive our environment, the most vital part is the retina, the thin layer of tissue that lines the back of the eye. This structure contains several layers of cells interconnected by synapses. When light enters through the eye, it passes all the way through the retina, until it is captured by photoreceptors. These cells then convert the light energy into tiny electrochemical impulses, which are processed by retinal neurons, before the signal is sent to the brain.
Loss of vision can have a huge impact on a person’s life. One particularly devastating disease, retinitis pigmentosa (RP), affects 1 in 400 people in the United States. Those affected by RP progressively lose their vision, beginning with night blindness, then loss of peripheral vision and eventually complete loss of all vision. Research into this disease has revealed that blindness occurs because the photoreceptor cells degenerate while the rest of the cells remain relatively unaffected. Because the rest of the retina is mostly functional in RP, scientists and biomedical engineers reasoned that prosthetic devices may be able to activate the retina similar to the way that photoreceptors do and partially restore vision.
Three months ago, the FDA approved the use of the first retinal implant in the United States. This enormous achievement is thanks to over 20 years of research, two clinical trials, and over $200 million in funding from the National Eye Institute, the Department of Energy, the National Science Foundation, and private investors. The ARGUS II Retinal Prosthesis System by Second Sight Medical Products, Inc. is an exciting success that gives hope to people who are blinded by retinitis pigmentosa.
ARGUS II is a biomedical implant consisting of both intraocular (inside the eye) and extraocular (outside the eye) components. In this system, a patient wears a pair of glasses that has a camera mounted on it. The camera captures images of what the patient sees and the images are sent to a visual processing unit (VPU) that the patient wears on his or her belt. The VPU then converts the camera image into a digital code. This code is sent wirelessly to electronics that are implanted on the outside of the eye. These electronics decode the information to produce a pattern of stimulus pulses that are then transmitted to electrodes that are arranged on the patient’s retina. The electrodes stimulate the surviving neurons in retina in a way that represents the image that the camera captured, thus bypassing the first step of visual processing. When these neurons are stimulated, they send signals to the brain that allow the patient to perceive their surroundings.
ARGUS II restores functional vision, but it is not the same as natural vision seen by patients before blindness. It is described as “somewhat pixelized” with spots of light covering a small region of the visual field. Even with its imperfections, some patients with the device are able to perform tasks such as discerning forms, identifying large written characters, and identifying objects such as light sources.
The technology is long away from enabling the patient to see like normally sighted individuals. Nevertheless, it is giant leap from being able to see nothing!
Written by Navya S. Davuluri