Prosthetic visual-acuity limits

The ceiling on how well any current prosthesis can see, set by phosphene density, current or light spread, electrode or pixel count, cortical magnification, and the surviving circuit's fidelity, not by camera resolution. Delivered acuities remain far below normal: early epiretinal devices reached only very coarse grating acuity, while subretinal photovoltaic implants have approached, roughly, the acuity implied by their pixel pitch.

Classic pixelized-vision studies suggest that on the order of several hundred well-placed phosphenes in a modest central field (tens of degrees) suffice for reading and mobility, a target that motivates high-density arrays but assumes clean, independent phosphenes rather than the streaked, fading, interacting percepts real devices produce. Closing the gap is as much a perceptual and encoding problem as an electrode-count problem.