The first product to show you how to keep your eye on the ball. Developed by an optometrist who has worked with some of the highest paid hitters in baseball, the I-ON adjusts to block any hitter's peripheral vision and builds the necessary muscle memory to track the ball closer to the point of contact against live pitching. Endorsed by 5 time All-Star Todd Helton and includes instructional DVD with recommended drills. For use in baseball and softball training. One Size.