At least 25-30 million people worldwide have age-related macular degeneration (AMD), one of the leading causes of blindness in middle-aged and older adults. Israeli start-up Nano Retina has announced its new Bio-Retina, a tiny array of photodetectors which can be implanted directly on the retinal surface. Ready to enter clinical trials in 2013, the Bio-Retina restores vision to AMD sufferers almost immediately following the simple implantation process.
The retina is a light sensitive tissue lining the inside rear surface of our eyes. Retinal tissue is layered, where the photoreceptors of the eye (rods and cones) are located beneath several layers of neurons and ganglia interconnected by synapses. These neurons transmit the image to the optic nerve, and the ganglia perform low-level processing of the visual information.
AMD is caused by deterioration or breakdown of the retina's central region, which is called the macula. It is a small area in the retina that is responsible for a person's central vision and which allows you to see fine details. AMD progressively destroys the ability of the rods and cones to convert light into signals transmitted along the optic nerve. A retina affected by AMD still has fully functional optic nerves, as well as the retinal subsystems which feed neural signals from the rods and cones into the optic nerve. But when the rods and cones are inactive, there are no light-generated neural signals for the rest of the retina to transfer. AMD patients often retain some peripheral vision, but their central vision usually disappears completely in time, resulting in legal blindness. Total blindness is also common. There are currently no effective treatments for AMD.
Nano Retina has now developed the Bio-Retina - a tiny (3 x 4 mm) microchip implant that is inserted into the eye and glued to the retina in a minimally invasive procedure. It does not treat AMD, but rather seeks to relieve the blindness resulting from AMD. A small slit is cut in the eye under local anesthesia, and the implant is inserted and pressed against the damaged macula.
The Bio-Retina uses the optical system (lens, iris, and pointing and focusing musculature) of the eye. It consists of an integrated circuit with a grid of photodetectors, microelectrodes and microelectronic circuitry that replace the eye’s natural photoreceptors and feed visual information through the healthy retinal structures to the optic nerve and the visual centers of the brain. The patient does not have to learn to interpret jumbled images, as the photodetectors measure the incoming light in a particular location on the image, and then stimulate the optical neurons immediately below the spot where the light would have hit in any case. In most cases immediate, normal feeling sight will be returned to the patient. The image is only in grayscale at this point, but color implants are not beyond the reach of this basic technology.
Beginning next year, the first clinical studies will be carried out with a 24 x 24 pixel grid (576 photodetectors), while later rounds of the clinical studies will have a 72 x 72 pixel grid (5184 photodetectors). For comparison, the Argus II retinal implant, now approved for use in Europe, provides roughly an 8 x 8 pixel grid. The figure below gives a feeling for how much vision corresponds to different sized arrays.
Clearly at the smallest resolutions there is little effective sight - even at 10 x 10 pixels, one would see little more than presence or absence of a large object. At the early Bio-Retina resolution of 24 x 24 pixels, one can clearly make out there is a person wearing a hat, and even that the person is probably female, while the later Bio-Retina resolution of 72 x 72 pixels is rather like watching an old black and white TV image. Perfectly usable, if not exactly exciting - unless a moment ago you were blind!
One problem remains. To detect light and electrically stimulate the visual neurons requires a source of electrical power. Nano Retina solved this problem rather elegantly. The microchip implant was also given a very small photovoltaic cell, pointing toward the lens of the eye. The implant user wears glasses which are perfectly normal, except that they incorporate a near-infrared battery powered laser directed into the eye. The laser light is invisible and harmless to the eye, but can drive the photovoltaic cell to deliver as much as three milliwatts of electrical power - more than enough to power the implant. The movie below gives an excellent overview of the Bio-Retina and its clinical use.
Blindness following a lifetime of good vision is often a terrible blow to people hoping to complete their careers and enjoy retirement. Sight is so much a part of how we experience the world that the true consequences of its loss are beyond the capability of most of us to imagine. With luck, further development of this sort of research will prevent future generations from having to face this situation.