Measuring phase aberrations using a pyramid wave front sensor

The pyramid wavefront sensor (PWS) was initially proposed by astronomers to measure aberrations introduced by the atmosphere. More recently it has been used to measure aberrations of the human eye, and has been successfully incorporated into an adaptive optics loop to correct those aberrations. The raw sensor signal can be used as feedback to control a wavefront correcting device, or with appropriate scaling, to reconstruct the wavefront map in the pupil. In practice, use of dynamic modulation allows one to tune the sensitivity and range of the sensor to best suit the particular application. We describe a PWS primarily designed to perform in-vivo measurements of human eyes. The sensor is calibrated over a wide range of settings allowing one to choose those best suited to a specific task. For example, enhanced-sensitivity measurements of very small aberrations require small range (closed loop adaptive optics). Alternatively, if one wants to measure the aberrations of the eye without any correction, the range required is subject-dependent and can be large; the price paid is in reduced sensitivity. We present in-vivo measurements of human eyes taken at a number of experimental settings and compare the performance of the PWS at each.