An improved laser interferometer allows forced choice contrast sensitivity measurements that are relatively unaffected by optical blurring in the eye. At spatial frequencies above about 60-70 c/deg, the regular bars of the interference fringe are no longer visible; observers report a pattern resembling zebra stripes centered on the line of sight. The characteristics of this pattern are consistent with the hypothesis that it is a moiré pattern resulting from aliasing by the foveal cone mosaic. Properties of this moiré pattern allow an assessment of the regularity of the foveal lattice, the spacing between cones, and the light-catching area of individual cones.