A head-mounted display system comprises a frame, an imaging system and an optical system. The frame is configured to be mounted to a head of a user. The imaging system is configured to couple to the frame, and includes one or more display devices disposed on a substrate and one or more sensors disposed on the substrate. The optical system is configured to provide an optical path between an eye of the user and the one or more sensors, and configured to provide the same optical path between the eye of the user and the one or more display devices.