Subretinal Implants

Eric Shine
Engineering Biomedical Systems
July 24, 2008

Subretinal Implants

The subretinal implant strategy will likely work the best in the future. Subretinal devices contain hundreds to thousands of light sensitive microphotodiodes that get stimulated by light. The stimulation passes from the photodiodes to microelectrodes that send the electrical signal to the optic nerve; from the there the signal goes to the visual cortex of the brain. Subretinal prostheses have a number of advantages over epiretinal devices. One is that the microphotodiodes placed directly over the damaged photoreceptor cells. Also since these devices do not rely on wireless interfacing with an external camera the signals between the devices the chances of a disturbance is less likely to happen. Another advantage with subretinal prosthesis is because the person with the device can still focus on objects with there eyes.Also there are aesthetic advantages has well, people do not have to where glasses with camera which could be unpleasing, as well, people who have epiretinal implants have to maintain, and keep up with the camera / glasses. One major downside to having either subretinal / epiretinal impants, the networking between the retina and the brain via the optic nerve must not be damaged.

Currently subretinal devices under testing that use the light received through the eye as a power source, like a solar panel; even though it is not the most powerful devices on the market, compared to an epiretinal and subretinal devices that have an external powersource, this type of device shows the most promise. This type of subretinal device would only have to consist of one chip that would contain a power source, mircoelectrodes and microphotodiodes. Since this type of device would only require one chip methods for implanting this device could be improved to make surgery less complicated and less time consuming. I believe this type of retinal device is the better of the two because it is less noticeable, it has a simple design, and the imaging capability is comparable to an epiretinal device.

References:
www.sciencemag.org/cgi/content/full/295/5557/1022
ieeexplore.ieee.org/iel5/2220/35447/01683653.pdf