Methods and systems are provided for enabling quantification and categorization of levels of user engagement of a user while wearing a head mounted display (HMD) and being presented virtual reality (VR) content. A computer-implemented method includes presenting a VR scene to an HMD user via display of the HMD and capturing one or more images of an eye of the HMD user while the HMD user is wearing the HMD and being presented with the VR scene. The method also includes operations for analyzing the one or more images for obtaining a pupil size measurement of the eye of the HMD user and for obtaining pupil size indicators usable to correlate pupil size measurements with user engagement. The method may also determine a level of user engagement based on the pupil size measurement and the pupil size indicators.
