Abstract: Systems, methods, and apparatuses for an eye tracking system to track eye movement via a camera and lens module utilizing a low-profile phase element, such as a holographic optical element (HOE), or a multipurpose sensor are provided. Systems and methods may include a multipurpose sensor to detect changes in light and determine occurrence of eye movement, a lens module (e.g., waveguide) configured to project an image covering a first field of view within an eye relief zone, to a camera positioned adjacent to the lens module and configured to track eye movements within a second field of view, and a low-profile phase element positioned in front of the camera. Light reflected from the user's eyes is transmitted via lens module to the camera which responds to eye reflection data of the second field of view. Systems and apparatuses for a calibration system to perform key performance indicator testing for eye tracking systems are provided.