The Optical Illusion of 20/20 Vision

By Dr. Leonard Press

Let’s start from the end of a concept and work our way back toward the beginning. After experiencing the benefits of optometric vision therapy, many patients (or parents of 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 parents whose children have had to struggle with learning and reading for years before they finally received needed help, don’t ask this question out of mere curiosity. They’re perturbed, and don’t want others to struggle needlessly before finding help. They wonder how and why visual conditions that benefit from vision therapy could be overlooked by professionals who are doing a credible job.

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!

To help create better awareness of the limitations of the eye chart as it relates to learning and performance, the National PTA passed a resolution in June, 1999 encouraging parents, teachers, doctors and other professionals to become more aware of these issues. Many schools now understand, for example, that putting on headphones and raising your hand to indicate that you heard a certain tone may indicate that you have perfect hearing, but it tells you little if anything about “central auditory processing” (listening skills for optimal learning and performance). It’s time for these professionals to recognize that seeing the 20/20 line on an eye chart may indicate perfect eyesight, but that it tells you little if anything about “visual information processing” (visual skills for optimal learning and performance).

To support the National PTA Resolution, we have now adopted the policy in our office of wearing pins that show a standard eye chart with a red circle and line through it. The purpose of this pin is to create awareness that you can have 20/20 eyesight yet still have vision problems that affect learning. Patients of all ages can have 20/20 eyesight, yet benefit from optometric vision therapy for visual problems having more to do with insight than eyesight. While most processes related to eyesight occur in the eye, most processes related to vision occur in the brain. Seeing a line of print doesn’t do you much good if you can’t visualize what it means. Should anyone tell you that you or your child has perfect vision because you can see 20/20, we’ll be happy to give you a red-lined pin that you can pass along. Together we can shatter the illusion that seeing 20/20 sized letters means perfect vision.