To use the visible fluorescent signal for wavefront sensing in scattering tissue at depth, we need to employ indirect wavefront sensing methods. In this section, we describe a pupil-segmentation AO method based on physical principles similar to those utilized by SH sensors. A zonal approach by nature, it differs from the wavefront measurement scheme in a SH sensor in that, rather than measuring the wavefront segments in parallel and thus being susceptible to tissue scattering as in a SH sensor, it measures the wavefront segments serially, making it applicable to strongly scattering samples such as the mouse brain.