An augmented reality (AR) eyewear device has a lens system which includes an optical screening mechanism that enables switching the lens system between a conventional see-through state and an opaque state in which the lens system screens or functionally blocks out the wearer's view of the external environment. Such a screening mechanism allows for expanded use cases of the AR glasses compared to conventional devices, e.g.: as a sleep mask; to view displayed content like movies or sports events against a visually non-distracting background instead of against the external environment; and/or to enable VR functionality.