A head-mounted display (HMD) includes an eye tracking system that determines user's eye tracking information based on depth information derived from time-of-flight methods. The eye tracking system includes an illumination source, an imaging device and a controller. The illumination source illuminates the user's eye with a temporally varying irradiance pattern. The imaging device includes a detector that captures temporal phase shifts (temporal distortions) caused by a local geometry and the illumination pattern being reflected from a portion of the eye. The detector comprises multiple pixels, each pixel having multiple units for capturing, over multiple time instants, light signals related to the temporally distorted illumination pattern. The controller determines phase differences between the temporally distorted illumination pattern and the temporally varying irradiance pattern, based on the captured light signals. The controller determines depth information related to eye surfaces and updates a model of the eye, based on the phase differences.