Biotechnology is offering a lot of promise for the vision impaired who still have functioning optic nerves. When the optic nerve is fine, it usually means the retina is not working. Retinal diseases include retinitis pigmentosa (RP), age-related macular degeneration (AMD), and diabetic retinopathy. Retinal diseases result in the light-sensitive rods and cones (photoreceptors) in the retina to stop working. In healthy eyes, the photoreceptors take light and turn it into tiny electrochemical impulses that are sent through the optic nerve to the brain for decoding into images. When the photoreceptors stop working effectively, the initial conversion process fails and the brain cannot translate the light into images.
Bionic eye implants focus on the initial conversion process with the photoreceptors to relay the impulses to the optic nerve. In order to do this, some sort of transmitter is needed behind the retina. The key to better imaging is more electrodes, and thus higher resolution. Although many research groups are working on bionic eyes with even more electrodes, there hasn’t been much progress on sensors or encoder chips that can create a color image. A lot of work is being done on understanding how the retina, optic nerve and brain process and perceive images.
Bionic eye implants do not provide anything like normal vision. It is not some blurry or grainy version of the vision a patient once had; it’s very abstract. Objects are made up of light streaks or dots of light that are somewhere in space but there’s no context. The objects are seen as a light form of shape approximately where one is looking, but he or she cannot tell how far away they are. Therefore, it can take a bit for the mind to adjust to interpreting these abstract light images into a meaningful concrete image. Nevertheless, this abstract form of vision can help the vision impaired to see doors and windows, recognize an object, stay on a sidewalk and differentiate between a white and black shirt. In some cases, people with bionic eye implants are even able to read.
The only bionic eye implant currently available in the United States is Second Sight’s Argus II. It was approved for use by the FDA in February 2013, although it was approved for use in Europe in March 2011 and was implanted in 30 U.S. patients in a clinical trial that started in 2007. It is designated for those in the late stages of RP and surgeons in Los Angeles, San Francisco, Philadelphia and Baltimore have been trained in the surgery to implant the device, which is expected to last 10 years. The new device uses a tiny video camera attached to eyeglasses that transmits images to a sheet of electrode sensors that have been sewn into the patient’s eye. These sensors then transmit those signals to the brain via the optic nerve. Unfortunately, this means that patients with glaucoma won’t benefit from the implant, as the disease damages the ocular nerve. The Argus II requires a 4-hour operation to install an antenna fitted with 60 electrodes behind the eye(s) and into the retina. This creates the equivalent of a 60-pixel display for the brain to interpret. Dr. Robert Greenberg, president and CEO of Second Sight Medical Products, Inc. said the device does not restore full vision, but does give patients what he calls “low vision” meaning it lets them perform visual tasks that they couldn’t otherwise do. “This is only the first step,” Greenberg said. “One of the great things about the Argus II system is that it is a software-driven system and we expect to be producing software upgrades for all the implanted patients.” Current lab work suggests those upgrades will include color vision and sharper images and Greenberg said they are working on more advanced implants. The Argus II is considered the most advanced prosthetic to date, and several publications including Time, CNN and Scientific American have called the Argus II one of the most important inventions of 2013.
Increased accuracy of images requires more electrodes in the implant but the challenge is in keeping it tiny. The planned Argus III will likely include 240 electrodes. This more powerful implant won’t be approved and available for several years.
Another bionic eye implant in development is the Bio-Retina by Nano Retina. It costs less – $60,000 instead of $100,000 – and rather than an external camera, the vision-restoring sensor is actually placed inside the eye, on top of the retina. The operation only takes 30 minutes and can be performed under local anesthetic. The Bio-Retina plops a 24×24 resolution (576 pixel) sensor right on top of the damaged retina, and 576 electrodes on the back of the sensor implant themselves into the optic nerve. An embedded image processor converts the data from each of the pixels into electrical pulses that are coded in such a way that the brain can perceive different levels of grayscale. The Bio-Retina system comes with a standard pair of corrective lenses that are modified so that they can fire a near-infrared laser beam through the iris to the sensor at the back of the eye. The sensor has a photovoltaic cell that produces up to 3 milliwatts. The infrared laser is invisible and harmless. Human trials of Bio-Retina are scheduled to begin in 2013.
By Angela S. Hoover, Staff Writer