in order to be a candidate for a retinal implant. This can be assessed non-invasively using optical coherence tomography (OCT) imaging. Other factors, including the amount of residual vision, overall health, and family commitment to rehabilitation, are also considered when determining candidates for retinal implants. In subjects with age-related macular degeneration, who may have intact peripheral vision, retinal implants could result in a hybrid form of vision. In this case the implant would supplement the remaining peripheral vision with central vision information. Types There are two main types of retinal implants by placement. Epiretinal implants are placed in the internal surface of the retina, while subretinal implants are placed between the outer retinal layer and the retinal pigment epithelium. Epiretinal implants Design principles Epiretinal implants are placed on top of the retinal surface, above the nerve fiber layer, directly stimulating ganglion cells and bypassing all other retinal layers. Array of electrodes is stabilized on the retina using micro tacks which penetrate into the sclera. Typically, external video camera on eyeglasses acquires images and transmits processed video information to the stimulating electrodes via wireless telemetry. An external transmitter is also required to provide power to the implant via radio-frequency induction coils or infrared lasers. The real-time image processing involves reducing the resolution, enhancing contrast, detecting the edges in the image and converting it into a spatio-temporal pattern of stimulation delivered to the electrode array on the retina. The majority of electronics can be incorporated into the associated external components, allowing for a smaller implant and simpler upgrades without additional surgery. The external electronics provides full control over the image processing for each patient. Advantages Epiretinal implants directly stimulate the retinal ganglion cells, thereby bypassing all other retinal layers. Therefore, in principle, epiretinal implants could provide visual perception to individuals even if all other retinal layers have been damaged. Disadvantages Since the nerve fiber layer has similar stimulation threshold to that of the retinal ganglion cells, axons passing under the epiretinal electrodes are stimulated, creating arcuate percepts, and thereby distorting the retinotopic map. So far, none of the epiretinal implants had light-sensitive pixels, and hence they rely on external camera for capturing the visual information. 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. Therefore, patients with