Retinal prostheses have had a long history and now include more than 15 companies and research groups in six countries. Those currently in or near human testing include:
- Boston Retinal Implant Project – Boston, Massachusetts
- Second Sight – Sylmar, California
- Retina Implant AG – Reutlingen, Germany
- Intelligent Medical Implant – Bonn, Germany
- Epi-Ret – Bonn, Germany
The two groups that appear to be further along in development are Second Sight and Retina Implant AG.
Second Sight Argus II Prosthesis System
The Second Sight device uses a camera and transmitter mounted to eyeglasses, an implanted receiver, and an array of electrodes secured to interface epiretinally with retinal ganglion cells. A battery pack worn on the patient’s belt powers the system.
The camera captures images as the subject’s head moves to view objects and track movement. These images are processed by the transmitter and receiver and turned into electrical impulses on the epiretinal array. These electrical impulses are intended to stimulate the retina’s remaining cells and generate corresponding perception of patters of light in the brain, which patients interpret as meaningful images.
Retina Implant AG Prothesis
The Retina Implant AG prosthesis doesn’t have an external camera. Rather, it uses a light-sensitive microchip that is surgically implanted under the retina, in the macular region where photoreceptor cells are located. The implant moves with the eye, which provides for “more natural processing of the image.” Aside from the subretinal micro-photodiodes, the only other equipment is a power module implanted behind the ear.
It is my expectation that the Retina Implant AG will probably prove to be the most helpful artificial vision device for restoring useful vision in patients with retinal dystrophies and possible dry age-related macular degeneration. There are multiple reasons for this point of view:
- The device’s imaging functionality of the implant is in the eye, hence being coupled with eye movement.
- They were able to report letter reading, providing strong support for functional vision via electrical stimulants.
- Personal communication with Dr. Robert MacLaren in Cambridge, England, a surgeon who so far implanted six of these devices, stated that, “A great advantage of the subretinal device is that it moves with the eye and is therefore in a more natural position for acquiring a retinal image.” He also added, “The use of the bipolar cells also adds an additional level of processing on top of the epiretinal approach developed by Second Sight.”
- It is presently being studied at Wills Eye Institute in Philadelphia, Pennsylvania with Dr. Jay Federman. Its light sensitivity certainly is a great advantage for the Retina Implant AG. Stimulating the bipolar/horizontal cells from the subretinal space rather than ganglion cells from the retinal surface seems more physiological.
There are an estimated 1.2 million people worldwide with retinitis pigmentosa, including 100,000 in the United States. We can give our patients hope for improved vision in the future. The devices are well tolerated in the eye, and as the quality of the devices gets better, we may be able to show that there is real benefit from them for improved vision to change people’s lives.