20/20 does not mean perfect vision. 20/20 is a measurement of how clearly you see in the distance.
If your standard vision test reports 20/20, it means that you are able to see clearly at 20 feet what should normally be seen clearly at 20 feet. On the other hand, if you have 20/40 vision, it means that you need to stand as close as 20 feet to see what a person with normal vision can see clearly at 40 feet.
The 20/20 test does not test how well you see at reading distance. In fact, the 20/20 test fails to evaluate many other important aspects of normal vision such as
- Eye focusing
- Eye coordination
- Eye teaming (binocular vision)
- Eye movement
- Visual perceptual skills
- Color vision
A Comprehensive Vision Exam tests all of the above, as well as visual acuity.