Smart eyewear devices may serve as advanced interfaces between cyber-physical systems (CPS) and workers by integrating digital information into the visual field. We have addressed ergonomic issues related to the use of a ruggedized head-mounted display (HMD) (Liteye 750A, see-through and lookaround mode) and a conventional screen during a halfday day working shift (N=60). We only found minor physiological effects of the HMD, resulting into inflexible head posture, higher muscle activity over time of the left M. Splenius capitis and low performance given its look-around mode.