Accurate gaze direction measurements with free head movement for strabismus angle estimation.

We present the Delft Assessment Instrument for Strabismus in Young children (DAISY) a device designed to measure angles of strabismus in young children fast and accurately. DAISY allows for unrestrained head movements by the mean of a triple camera vision system that simultaneously estimates the head rotation and the eye pose. The device combines two different methods to record bilateral eye position: corneal reflections (Purkinje images) and pupillary images. Detailed results are provided on three orthotropic subjects (age 25-27). Three different conditions were tested: 1) gaze ahead, 2) gaze ahead with different head rotations, and 3) fixed head with different eye positions. Systematic errors occurred between subjects that need further study. The system reached sufficient accuracy to be applied for the measurement of angles of strabismus, almost independent from the head pose.