What limits spatial perception with retinal implants?

An overview of factors affecting spatial perception with retinal implants is given. Results from clinical trials are summarized, which show a best visual acuity of 6/330 and a rudimentary level of functional vision. Further improvement in the spatial perception provided by retinal implants is required to perform tasks like face recognition and reading, which potential recipients list as being highly desirable capacities. The psychophysical requirements of prosthetic vision required to perform these task are summarized based on experiments from simulated prosthetic vision. Finally, the contributions and limitations of surgery, hardware and stimulation strategy to meeting these requirements are discussed.