Scientists at the University of California San Diego have developed a soft tunable lens that automatically shifts focal length when the wearer blinks twice (Li et al, 2019). 

The basic principle behind this technology is electrooculography: the measuring of corneo-retinal standing potential between the front and the back of the eye. This changes in known ways when the eyes move in different directions, and typically a pair of electrodes attached to the face can then ascertain which way the eye is moving, and whether blinking has transpired.