Topography of the foveal cone mosaic in the living human eye.

Interference fringes whose spatial frequency exceeds the resolution limit form visible moiré patterns with the foveal cone mosaic. This paper describes a model of foveal cone sampling that shows how these moiré patterns depend on the spatial frequency and orientation of an interference fringe imaged on a triangular lattice of cones. The model is tested with two psychophysical experiments. The first experiment shows that the behavior of the moiré patterns is quantitatively consistent with anatomical estimates of cone spacing across the human fovea. These patterns provide a psychophysical method for measuring cone spacing within 1.75 deg of the foveal center. In some observers, cone spacing is larger in a horizontal direction than in a vertical direction at any particular location within the fovea. The second experiment shows that the behavior of the moiré patterns is consistent with the triangular packing of foveal cones observed anatomically, and allows the orientation of the cone mosaic to be determined at the foveal center. These observations demonstrate the rich information that methods based on aliasing can provide about the topography of foveal cones in the living human eye.