The MREAL System for Mixed Reality (that's the full name -- or, if you want to drill down even further: the headset is the HM-A1 and the software platform is MP-100) generates video of one's surroundings using a pair of cameras positioned in front of the wearer's eyes, which is combined with computer-generated graphics.

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Vision breaks are not just important for your eyes - research at Cornell University in New York State has found that computer workers who take short breaks are more productive than those who don't take breaks.

BBC: Computer eye tests