Belay glasses (aka Belaggles) save your neck from strain and injury if you climb or top-rope regularly. I have found them to be even more useful and convenient when on lead belay, because you are able to keep an eye on both your climber and the amount of slack you are giving them.
Rock climbers and mountaineers use Belaggles to help alleviate neck pain from belaying. They allow you to keep your head straight, but see upward. With rubber nose pads, to prevent the Belaggles from slipping off your face, and a retainer cord keeps them in place when your climber falls.
Belaggles construction’s idea comes from those reading glasses originally built for older folks to read books and watch TV while laying in bed – how genius! Now-a-day people look down to stare at their cell phones, and climbers stare above to watch their partners.
Any number of activities that force you to hold your head up or down for long period of time can be straining on your neck, eventually causing long term injuries.