Image sampling properties of photoreceptors: a reply to Miller and Bernard.

Miller and Bernard argue that photoreceptor sampling occurs at the inner rather than outer segments. Foveal inner segments form a lattice-like array that should create visible Moiré patterns when frequencies above 60 c/deg are image by interferometry. Despite a checkered past, this prediction is confirmed by recent experiments. Extrafoveally, frequencies above the nominal Nyquist limits of the cones are routinely present in the retinal image. Spectral analysis shows that the inner segments there form optimally irregular sampling arrays that avoid Moiré distortion by scattering supra-Nyquist frequencies into broadband noise. Thus is appears that topological disorder in the receptor mosaic prevents aliasing outside the fovea--the only place it could occur in normal vision.