We loaned 20 children an iPad with a touch-sensitive screen and asked them to play a game at home for 1 hour a day, 5 days a week for 2 weeks (10 hours total).
Dig Rush, an engaging action-oriented game, requires the child to use their finger to manipulate miners and their surroundings to dig for gold and return it to a cart as quickly as possible while avoiding obstacles such as fire, lava, and monsters (described in Ref.
24). There are 42 levels that increase in difficulty and the child can earn up to three stars per level (maximum star count = 126). The child can use gold to purchase items to help them dig faster and carry more gold, as well as more miners and digging tools (
Fig. 1A).
Children played the game while wearing red-green anaglyphic glasses that separated game elements seen by each eye. Reduced contrast elements (e.g., gold, fire) are seen by the fellow eye, high contrast elements (e.g., miners, monsters) are seen by the amblyopic eye, and high contrast background elements (e.g., ground, rocks) are seen by both eyes. In order for the child to play the game successfully, both eyes must see their respective game components. Contrast in the amblyopic eye remained at 100% contrast, while contrast in the fellow eye started at 20% but increased with game success (i.e., a star earned). At least 18 hours of game play was required to reach 100% contrast, thus ensuring no child maxed out at 100% after 2 weeks (10 hours) of treatment. If game play was unsuccessful for 30 minutes (no stars earned), fellow eye contrast was reduced. Prior to enrollment, the experimenter ensured that the child could see all elements of the game wearing the red-green glasses. Children were familiarized with the game and practiced until the experimenter was confident in their ability to understand and play the game.