The lenslet array creates spots in the sensor according to the wavefront coming out of the eye. Inverse of the Shack–Hartmann system in optometry: A set of patterns is displayed on the screen, the user aligns/overlaps them in a single image pressing buttons. A schematic illustration of a SHWFS. Operations of a single lenslet in a SHWFS. A Shack–Hartmann (or Hartmann–Shack) wavefront sensor.