Consistantly hitting a baseball requires exceptional visual skills that are most challenged by speed, extraneous motion and peripheral distractions.
To get the eyes to work better in baseball the visual system's processing speed needs to be ramped up so the player can see and react more quickly and efficiently.
The importance of eye speed can be clearly considered when you think of when you see a red light, and then step on the brakes. Their “visual brain” processing speed defines how fast you can register and identify an external visual stimulus—the red light. Their “motor brain” controls their motor speed of physical reaction time, defines how fast you can react to it—step on the brakes.