Vision is the dominant sense in humans. Through Vision we receive 80% of all information arround us. Vision is the deriving of meaning and direction of action as triggered by light. Vision is much more than sight or how clearly one sees, which is commonly measured and termed acuity. Vision is one's comprehensive ability to organize that which can be seen in such a way that one understands what is seen and can use that understanding to guide and direct one's actions. 

20/20 acuity DOES NOT necessarily mean good Vision. Many other VISUAL SKILLS needs to be functioning well for Vision to be effective.