Over the past decade, extended reality (XR) applications have increasingly been used as assistive technology for people with low vision (LV). Here we present a systematic literature review of 216 publications from 109 different venues assessing the potential of XR technology to serve as not just a visual accessibility aid but also as a tool to study perception and behavior in people with low vision and blind people whose vision was restored with a visual neuroprosthesis. These technologies may be used to visually enhance a persons environment for completing daily activities, train LV participants with residual vision, or simulate either a specific visual impairment or the artificial vision generated by a prosthetic implant. We also highlight the need for adequate empirical evaluation, the broadening of end-user participation, and a more nuanced understanding of the suitability and usability of different XR-based accessibility aids.