This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The purpose of this study is to see if there are brain changes in people who have a retinal implant. Subjects will receive six Positron Emission Tomography (PET) scans with a radiotracer on six different days. PET is a special camera that takes pictures of the movement of a radiotracer in the body. The radiotracer for this study is 18FDG, which is a radioactive sugar that is injected into the bloodstream in very small amounts and will serve as an indicator of brain circuit changes. Glucose is the sugar the brain uses for fuel.