Tokametsuke was one of the physical trainings of Ninja (a secret agent in feudal Japan highly skilled in stealth and secrecy). It was used to improve eyesight. In Tokametsuke, an Andon (a paper-covered lamp stand) was lit in a dark room, and a reasonable number of holes were pricked on its parts made of Washi (Japanese paper), and from a distance, the numbers of those holes were counted. The exercise was carried out every day, and gradually the numbers of the holes were increased.
Another method which was passed down for improving eyesight was to repeatedly come and go between a dark room or a closet and a bright room.