Retinal implant
[6] The device may help adults with RP who have lost the ability to perceive shapes and movement to be more mobile and to perform day-to-day activities.
It completed a multi-centre clinical trial in Europe and was awarded a CE Mark in 2013, making it the first wireless epiretinal electronic device to gain approval.
[12] Other factors, including the amount of residual vision, overall health, and family commitment to rehabilitation, are also considered when determining candidates for retinal implants.
[4][13] The majority of electronics can be incorporated into the associated external components, allowing for a smaller implant and simpler upgrades without additional surgery.
Therefore, unlike natural vision, eye movements do not shift the transmitted image on the retina, which creates a perception of the moving object when person with such an implant changes the direction of gaze.
Future versions of the ARGUS device are being developed with increasingly dense electrode arrays, allowing for improved spatial resolution.
[15] The ARGUS II device received marketing approval in February 2011 (CE Mark demonstrating safety and performance), and it is available in Germany, France, Italy, and UK.
Another epiretinal device, the Learning Retinal Implant, has been developed by IIP technologies GmbH, and has begun to be evaluated in clinical trials.
The retinotopic stimulation from subretinal implants is inherently more accurate, as the pattern of incident light on the microphotodiodes is a direct reflection of the desired image.
[4] The main disadvantage of subretinal implants is the lack of sufficient incident light to enable the microphotodiodes to generate adequate current.
[18] The current version of this device has been implanted in 10 patients, who have each reported improvements in the perception of visual details, including contrast, shape, and movement.
[13] The Retina Implant AG device contains 1500 microphotodiodes, allowing for increased spatial resolution, but requires an external power source.
Retina implant AG reported 12 months results on the Alpha IMS study in February 2013 showing that six out of nine patients had a device failure in the nine months post implant Proceedings of the royal society B, and that five of the eight subjects reported various implant-mediated visual perceptions in daily life.
[19] Results from all clinical trials to date indicate that patients receiving subretinal implants report perception of phosphenes, with some gaining the ability to perform basic visual tasks, such as shape recognition and motion detection.
This experiment, therefore, not only demonstrated the functionality provided by low resolution visual feedback, but also the ability for subjects to adapt and improve over time.
The number of electrodes necessary for reading or room navigation may differ in implanted subjects, and further testing needs to be conducted within this clinical population to determine the required spatial resolution for specific visual tasks.
Simulation results indicate that 600-1000 electrodes would be required to enable subjects to perform a wide variety of tasks, including reading, face recognition, and navigating around rooms.
The clinical reports indicate that, even with low resolution, retinal implants are potentially useful in providing crude vision to individuals who otherwise would not have any visual sensation.
[13] However, clinical testing in implanted subjects is somewhat limited and the majority of spatial resolution simulation experiments have been conducted in normal controls.
[4] The Manchester Royal Infirmary and Prof Paulo E Stanga announced on July 22, 2015, the first successful implantation of Second Sight's Argus II in patients with severe Age Related Macular Degeneration.
