The Old Myth About Perfect Sight

The truth about 20/20

Sol Tannenbaum, OD, FAAO

There is an old myth going around.  It says that 20/20 vision is perfect sight.  And it just isn’t so!  Still the myth is perpetuated almost daily by people in the health care field who ought to know better.  They use the eye chart alone to determine “perfect” eyesight.  As a consequence, millions of children are led to believe that their eyes are ready to tackle the most challenging and exhilarating experience of their life—the elementary school entrance into the world of learning.


Myth carried too far

The myth would lead you to believe that each eye sees separately.  This belief holds true for the animal kingdom below man and monkey.  But for man, the most elementary books on biology or psychology will tell you differently!  The myth would imply that the distant vision so necessary to the life of the hunter or cave man is as necessary for the school child who is trying to read a book at his desk. 

The myth would also infer that it is not difficult to find visual disorders.  Why else would the eye chart be so firmly defended in every medical office in the land?  But alas, the myth is carried too far when it is extended to the visual screening of the preschool child.


The eye chart again

All authorities agree that true preventive eye care should begin at the earliest age level possible.  Find the problems early and in many cases they not only can be corrected but future visual disorders can be prevented.  At last we have the possibility for preventative eye care—the eye practitioner’s dream.  So what happens—in comes the eye chart again, but this time disguised as a tumble E with each eye being screened separately.  And once again, the preschool child is subjected to a distance test using one eye at a time.


Screening's deceit

This one-eyed screening for the pre-school child, school child, or the adult is not a screening test for amblyopia, muscle imbalance, poor coordination, hyperopic astigmatism, faulty fusion, suppression or anything else.  It is only a test for what each eye sees at a distance. 

If he fails the screening, we do not have the slightest idea what is wrong.  And if he passes the screening, we still haven’t the slightest idea what is right. 


We see with both eyes


For the fact of the matter is that you do not go around looking out of each eye separately.  You see out of both eyes open, together.  And when both eyes are wide open, one eye can be suppressing and not participating in the visual act with its partner.  Or you can see double.  Or one eye can expend more energy in focusing or in turning, or have small degrees of astigmatism.  And at the reading level you can have a terrible problem and still pass the distance screening. 


Problems can arise with two eyes

What does a monocular test—that is, each eye tested separately—tell you about the need to see clearly, singly and comfortably far and near?  You don’t have a problem if you use one eye only.  As a matter of fact you have made an adjustment and you are quite comfortable.  It’s when the two eyes are being used together that the problems arise. 


Problems are hard to find with one eye

The amblyope is not uncomfortable.  Neither is the cross-eyed person where one eye is turned all the way towards the nose and out of the visual act.  It is the two-eyed person who has co-ordination problems that are not severe enough to cause one eye to give up; it is the eye with conditions of astigmatism or hyperopia that are not great enough to give up but make two-eyed seeing very uncomfortable.  The eyes can have a vertical muscle imbalance or a horizontal muscle imbalance causing two-eyed seeing to be difficult. 

When each eye is tested separately the imbalance disappears because it is only present under two-eyed seeing conditions.


20/20 shouldn't be confusing

Doesn’t it make sense that since we are two-eyed seeing individuals, the same eye testing should be done under two-eyed seeing conditions?  Suppose that a man has one short leg and one long leg.  If you have him jump up and down on each leg separately, all you have learned is that each leg is functional.  But put him in a race and he will still stumble over his feet. 

Starting school is the biggest binocular seeing race of a child’s life.  The myth of 20/20 must be recognized for what it is—an area of confusion in the path towards visual health.


Reprinted with permission from Dr. Sol Tannenbaum by Vision First Foundation. Copyright © 2007 Vision First Foundation. All rights reserved.