Background: Baseball is the leading cause of sports-related eye injuries in young persons. It is known that softer baseballs reduce the potential for brain and cardiac injury, but it has been speculated that softer baseballs may increase eye injuries by intruding more into the orbit. It also has been claimed that softer baseballs would change the "feel" of the game.
Objectives: To determine the orbital intrusion and eye injury potential of baseballs of varying hardness, and whether a player can feel the difference between these different baseballs.
Main outcome measures: Orbital force and penetration of baseballs of various hardness into an artificial orbit. Ability of subjects of varying age and baseball experience to determine the hardness of baseballs.
Results: The peak orbital force and force onset rate from softer baseballs, at all impact velocities, were less than the force and force onset rate from baseballs that had hardness equal to, or greater than, major league baseballs. The softest (10% of major league hardness) baseballs intruded into the orbit significantly more than balls that were 15% of major league hardness or harder. Children younger than 14 years could not differentiate balls 15% of major league hardness or harder, and adults could not differentiate 20% of major league hardness or harder from each other or from major league balls.
Conclusion: The potential for injury to the unprotected eye from soft baseballs is significant, but not greater than that from a major league baseball. Baseballs that are 15% to 20% of major league ball hardness are recommended for youth baseball because these balls feel like major league balls, reduce the potential for brain injury and commotio cordis, cause less pain on impact, and do not increase the potential for eye injury to the unprotected player. Eye injuries in youth baseball could be minimized by the use of protective eyewear that conforms to the standard specifications of the American Society of Testing and Materials (Philadelphia, Pa), standards F910 (for batters and baserunners) and F803 (for fielders).