electronic glasses

The lenses contain a thin layer of liquid crystal that changes its alignment when prompted, thereby changing the strength of focus.
Each eight-hour battery charge allows for two-to-three days of switching between focus settings.

The frames have three settings - automatic, manual on and manual off - allowing the wearer to remain fully in control.

One potential drawback is their cost - a pair will set you back between $1,000 and £1,250, although that includes the frames, lenses , coatings and charger.