Four Emerging Vision-Enhancing Technologies: the Implantable Miniature Telescope, the Telescopic Contact Lens, the Argus II Retinal Prosthesis, and the Artificial Silicon Retina
The first television sets had screens barely larger than a postage stamp and were housed in bulky, console cabinets. Nowadays a 60-inch high-definition flatscreen can hang from your wall like a painting. We've certainly come a long way from the first wireless phones that were so large you needed a briefcase, or at the very least a bag, to carry one around.
Even our low-vision aids have benefited from the trend of "make it better, make it smaller." The first video enlargers and OCR reading machines often occupied an entire desktop. Today you can carry a substantially more powerful unit in your pocket. And is there anyone who would even consider lugging around a 10-year-old braille display to use with one of today's super-slim accessible cell phones?
Low vision technology solutions can help the visually impaired get the most use from limited vision, and these days the technologies have grown so small and powerful, you might not even have to carry them around with you. They're always on and always with you, because they work from right on top of, or even inside of, the eye itself.
In this article we'll take a look at four emerging technologies with the potential to enhance the useable vision of many individuals with age-related macular degeneration (AMD) and retinitis pigmentosa (RP). Three of them, the Implantable Miniature Telescope, the Argus II and Retinal Prosthesis System, and the Artificial Silicon Retina microchip (ASR) do at least a portion of their work from inside the eye. The fourth, an experimental telescopic contact lens, uses tiny mirrors to magnify and redirect images around damaged retinal tissue.
The Implantable Miniature Telescope
Monoculars and other magnification aids can be extremely useful to many individuals with partial vision. But imagine if you didn't have to remember to carry one with you, because it was always with you. That was the thinking behind the Implantable Miniature Telescope from VisionCare Ophthalmic Technologies. The device is no larger than a pea, and to date, nearly 400 individuals with end-stage age-related macular degeneration have received implants with a useable-vision success rate of over seventy-five percent.
How it Works
Macular degeneration damages the retina from the center out. As the sharper central vision is destroyed, people with AMD must increasingly rely on their peripheral vision, which is not nearly so adept at reading text, recognizing faces and the like. Magnification can help, which is where the Implantable Miniature Telescope comes in.
Recipients of the telescope undergo surgery similar to cataract removal. The natural lens of the eye is replaced with a small, one-piece, 2.75 magnification telescope. The device projects a magnified image onto the retina, which enables the peripheral vision to resolve significantly finer detail, such as print or faces.
"It took me several months to get used to seeing with the telescope," says retired engineer Dan Dunbar, who received his device in November of 2011. Dan, now 82, is a long time model train hobbyist, but by the early 2000s he had worked his way up the size scale from N-gauge through HO-gauge all the way up to O-gauge model trains to accommodate his lessening vision. Eventually he could no longer see his trains as they circled the far side of his eight-by-thirty-foot O-gauge layout.
After his surgery Dan underwent several months of eye exercises with a low-vision specialist. He was also fitted for a pair of glasses with a prescription lens for his left eye, which had the implanted telescope. The telescope is one-size-fits-all, but retinas are not. A corrective lens is usually also required to adjust the focus so it strikes the retina at the ideal focal point, much the same as prescription lenses do for nearsighted or farsighted individuals.
"At first, everything looked sort of muddy out of that eye," Dan recalls. "Then one day things just sort of clicked." There was still work to be done. "Doors looked larger and closer than they actually were," he says. "And I remember one day in the car with my wife, she made a right turn and the car seemed to lurch so fast, I felt like I was sitting way in the back of an amusement park bumper car ride."
The miniature telescope is implanted only in one eye, the better of the two. The other eye continues to provide peripheral vision to help with balance and orientation. Gradually, Dan has learned to switch his focus back and forth so his brain can assimilate the visual information gathered from each eye. "The magnified doorknob looks larger than it is, but my other eye tells me it's really not as close as it seems," he explains.
Enlarging the image projected onto the retina also causes the brain to interpret the area covered by the degenerated macula as having grown proportionally smaller, reducing the effect the blind spot has on central vision. "These days when I look someone in the eye, to me, their face seems dead center in my vision," Dan says, adding, "It's taken me a long time to get used to not having to turn my gaze to see what's in front of me."
Before his implant Dan's reading was limited to magnified text on his computer. Now he can slowly read the print in most paperbacks. He's also enjoying his trains more than ever. These days he can see them easily, even at the far end of the track.
The Telescopic Contact Lens
One day soon individuals with macular degeneration and others whose useable vision can be increased with magnification may be able to enjoy the benefits of an implantable telescope without having to undergo the surgery. That's because a team of researchers at the Jacobs School of Engineering at UC San Diego are developing a telescopic contact lens.
The wearable lenses are one millimeter thick, and their centers allow normal, non-magnified images to pass through. Within the outer edge, however, a collection of tiny aluminum mirrors create a ring-shaped telescope that magnifies images 2.8 times and helps the peripheral retina outside of the macula to resolve greater detail.
The lenses include polarization filters that allow light oriented in one direction to pass through the clear center and light oriented in another direction to strike the magnifying mirrors. 3D movies use special glasses to direct one image to the viewer's left eye and a slightly different second image to the right eye. These magnifying contacts will use similar glasses with liquid crystal shutters, only instead of sending different images to different eyes it will shift the polarization so it can pass through either the lens' clear center or the magnification mirrors, but not both.
Initially, users will flip a switch to toggle back and forth between regular and telescopic vision. But project leader Joe Ford and his team members are also working on a hands-free switch that will use an infrared LED to monitor when the user blinks with both eyes or winks with one eye to make the switch automatically.
The Argus II Retinal Prosthesis
Many individuals with little or no light perception can use light detectors (available either as stand-alone devices or via a number of smartphone apps) that can provide information about the environment, such as the position of doors and windows, via the location and strength of the edges between light and dark regions. That's the principle behind the Argus II Retinal Prosthesis from Second Sight Medical Products, which received FDA approval in February 2013 for the treatment of late-stage RP.
An inherited retinal degenerative disease, RP leads to blindness due to a progressive loss of the light-sensitive photoreceptor cells called rods and cones. Often the underlying retinal nerves are left undamaged, however, and the Argus II stimulates these nerves directly, bypassing the damaged rods and cones altogether.
The device includes an aspirin-size capsule implanted beneath the conjunctiva, the white of the eye, on the side nearest the temple. A tiny antenna receives both a wireless data signal and radio frequency power from outside of the eye, and then transmits these signals to a 4-by-6mm polymer array of 60 microscopic electrodes implanted on the retinal surface.
Argus II users wear special glasses with a miniature video camera mounted on the bridge. Each user also carries a Video Processing Unit (VPU) about the size of a deck of cards on his or her waist. The VPU powers the camera, processes the camera's video signal and then sends it back to the glasses, where a second, external antenna communicates with the implant from directly outside the eye.
Kathy Blake received the very first Argus II implant in a clinical trial in June 2007. Technicians spent several months activating the electrodes one by one, fine tuning the electrical current going to each so it was strong enough to trigger a response without being overwhelming.
"Gradually, I began sensing edges," says Kathy. "I would move my head from side to side, panning the camera, and when I scanned past a window, say, I would see a brief flash of contrast. In time, Kathy's ability to detect edges increased, along with her ability to sense the contrast in different shades of gray. "If I sit at the table and move my head side to side to pan the camera I can tell where the silverware is, and the difference between my plate and napkin," she says. "Walking with my guide dog, I can see the crosswalks, and if she stops and sits I can close my eyes to concentrate, scan ahead, and deduce, 'Oh, that's a car blocking the sidewalk.'"
The Video Processing Unit includes three special settings that can be customized for, and selected by, each user. In Kathy's case, the first is an invert mode that makes bright items dark and dark items bright, which Kathy uses outdoors so the bright sunlight doesn't cause everything to flash too bright. A contrast enhancement setting helps in dim light, and with this setting Kathy was able to pick out the lights on last year's Christmas tree. She can also sort her laundry, lights from darks, and match socks by placing items one by one against a white background. The third setting enhances edge detection, but, reports Kathy, "That one doesn't seem to make any difference for me."
Kathy uses the system for at least 15 to 20 hours every week. She's extremely satisfied with the results, but she's never expected miracles. "Mostly, I did it to participate in the research and maybe help things along," she says. Indeed, company scientists have used what they've learned from Kathy and other early implant recipients to continue to improve the device. Many recent recipients are able to perceive rudimentary colors. Others can distinguish letters less than an inch high without having to pan their cameras at all.
The Argus I used only 16 electrodes. The Argus II uses 60, and the company is planning to use even more in future versions. They have also begun tentative experiments with virtual electrodes, altering the signals in order to stimulate the retina between the electrodes, much as a stereo generates sound that seems to come from the far left, right, center or anywhere in-between.
The Artificial Silicon Retina
These days a growing number of low-vision aids contain at least one computer chip. Here's one that consists of a single slice of silicon.
The Artificial Silicon Retina (ASR) is a tiny computer chip, 2mm wide and one-third the thickness of a human hair, which is implanted in a surgically created sub-retinal pocket. The ASR contains approximately five thousand microphotodiodes, which are tiny solar cells that turn light into electricity, and then use that electricity to send extra stimulation to damaged rods and cones without the need for external power sources or glasses.
In the early 200os, Alan Chow, MD, Assistant Professor of Ophthalmology at Rush University, performed the first of a total of 42 ASR implants. "Over one-third of the recipients experienced the sensation of a light flash when the implant was stimulated," reports Dr. Chow. "However, all patients experienced an unexpected and even more important measureable improvement in their remaining central vision, including better perception of color, contrast, visual acuity and field size."
According to Chow, these improvements were more than could be explained from simple electrical stimulation of retinal cells. For some, the improvements took an unexpected, even more surprising turn.
"Not only did the vision in my right eye, the one with the implant, improve, the vision in my left eye also got stronger," says Melanie Furniss, a retired operations manager for a Fortune 500 company. Melanie has RP, and in 2004 when she received her implant her visual field was less than 5% and she could only read print with the help of an electronic magnifier.
A few months post-implant, Melanie began to perceive colors again. After a year she was reading regular print, and able to thread a sewing needle by sight. And when she held a hand over her right eye, "The vision was still too blurry to make out letters," she says. "But there was definitely an improvement in my left eye as well. My retina specialist confirmed that the rods and cones in both eyes looked healthier."
As to why Melanie and many other implant recipients experienced this sympathetic response, Dr. Chow offers this theory: "The implant works by inducing certain retinal cells to increase their production of neurotropic factors. This has now been shown in a number of published animal studies" he explains. "These factors can circulate in the blood stream, so the opposite eye could also be receiving the benefits."
Unfortunately, the improvements may not be permanent. Melanie and others report that after five or six years their vision peaked, and though it is still sharper than before their implants, in recent years the improvements have begun to diminish.
"We are currently testing methods that might help preserve a greater degree and longer duration of vision," says Chow. For now, a second implant is not possible. The group that invested in the original ASR implants could not afford the more than $200 million standard FDA approval would have required. Dr. Chow has reorganized the project, however, and this time he is hoping to obtain a humanitarian device exemption, which would cost significantly less.
The Implantable Miniature Telescope
VisionCare Ophthalmic Technologies, Inc.
Currently the Implantable Miniature Telescope is FDA approved only for individuals over 75 with end-stage age-related macular degeneration. The good news is the device is now eligible for Medicare reimbursement.
The Telescopic Contact Lens
Currently, the telescopic contact lens is still in the research phase, and has only been tested on a handful of military volunteers. The group hopes to begin clinical trials sometime later this year, but access to a waiting list and further information are not available to the public at this time .
The Argus II Retinal Prosthesis
Second Sight Medical Products, Inc.
The Argus II was FDA approved in February of 2013 for individuals over 25 years old with loss of all functional vision from retinitis pigmentosa, though the company is planning upcoming trials for individuals with age-related macular degeneration. By the end of 2013 the company plans to offer the device in 12 medical centers. The Centers for Medicare and Medicaid Services has approved the device for reimbursement, and at this writing one private pay insurance company, Health Net, also reimburses for the implant.
The Artificial Silicon Retina
Though no date has been set to resume ASR implants, several hundred people are currently on a waiting list to receive the device if and when it becomes available.
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