WHY 20/20 ISN’T PERFECT VISION
After experiencing help with specially designed lenses, prisms, or optometric vision therapy, many parents or patients ask us the same question: “How is it that we saw other eye doctors before you, and were told that our (or our child’s) vision is “perfect”?
The answer is actually quite simple. It all depends on how the professional, whether it’s a school nurse, a pediatrician, or an eye doctor, defines “perfect vision”. All too often, the person using this phrase is referring to how well you can see the eye chart. Devised in the 1800’s by an eye doctor (Snellen), this chart took 20/20 as an arbitrary standard of what size letter most people who didn’t need glasses agreed that they could see from a distance of 20 feet.
So all that 20/20 eyesight means is that you can see the “20 size letter” at a distance of 20 feet. If we have to make that letter larger in order for you to see it, then the bottom number will be larger (someone seeing 20/40 is twice as blurry as someone seeing 20/20). Okay, you might be thinking: If 20/20 means perfect eyesight, what’s the difference between perfect eyesight and perfect vision? Do we mean that someone might not need eyeglasses to see clearly, yet still have a vision problem?
Absolutely! And one of the best ways we’ve seen to think about this comes from the American Optometric Association’s “School Nurses Guide to Vision Screening”:
“Vision is the process of deriving meaning from what is seen. It is more than the concept of visual acuity, clearness of sight, or 20/20 vision. Good vision also involves the ability to use the eyes for extended periods of time without discomfort, to analyze and interpret information and to respond to what is being seen. Vision is the learned ability to see for information and performance; it allows us to understand things that we cannot touch, taste, smell or hear. Vision is the process by which we perceive space as a whole. Good vision goes beyond 20/20 visual acuity, good optics and normal eye health. It involves normal binocular vision, ocular motility and vision information processing skills, which allow us to respond to our environment.”
Hopefully you now have a clearer picture of why professionals who tell you that you (or your child) have perfect vision based on seeing the eye chart clearly (with or without glasses or contacts) have adopted a very narrow viewpoint on vision. It’s the same view that Dr. Snellen took in the 1800’s, and vision science has certainly come a long way since then!