Retinal Prosthesis

There are two major categories of retinal prosthesis’ known as subretinal and epiretinal prosthesis, and they differ in the location of their light receptors. As their names imply, subretinal means the artificial photoreceptors are located underneath the retina, and epiretinal means they are on top of the retina. Based on these characteristics alone, the subretinal would seem to be the wisest choice for a patient wanting to restore their vision; having eyes outside of your head is unnatural and makes them more prone to damage. Neither can you move them like you can your eyes. However, there are differences in their safety and ultimate effectiveness that go beyond the simple location of the light receptors.
Namely, these differences have to do with the way in which the device is connected to the brain. The major ways in which you can connect prosthesis with the brain are: 1 Implanting a MEMS (Micro Electrical Mechanical System) in the retina 2 Implanting a MEMS in the optic nerve 3 Implanting a MEMS into the skull 4 Implanting a hybrid retinal device. Out of all these methods, the most sophisticated and promising seems to be the hybrid retinal device for the following reasons.
Normal retinal and optic nerve implants cannot work if ganglion cells and the optic nerve are damaged, and would not be able to assist a majority of patients who suffer blindness. However, the solution for this problem, placing a MEMS in the skull, is a complex and dangerous procedure due mainly for increased chance of cell proliferation, whereas retinal and optic nerve implants can be installed/fixed with common and relatively safe procedures. Though there are others problems with all these implants, including power supply, difficulty in signal transmission, blurred images, and wear of artificial material, a hybrid retinal device succeeds where the other three do not; it is a relatively safe procedure and it does not require the optic nerve and/or retina to be intact. Like a cortical implant, it is epiretinal (a small put down, but in comparison to its advantages, insignificant), but unlike a cortical implant it uses neural grafts to build a connection through the damaged retina. The surgery required to implant it would be similar to retinal and optic nerve MEMS’, making it safer, and, when compared to other methods of connecting visual prosthesis, the obvious choice for the job.