A Theory of Letter Reversals in Dyslexia: A Proposed Neuromechanical Explanation
By Edward J. Harshman, M.D.

Dyslexia, the curse of modern reading teaching, has been credibly linked to neurotransmitters. Teaching methods, such as phonics vs. whole-word methods, have also been studied. Lost in the analysis, however, is long-forgotten work including an analysis of neurophysiology that accidentally includes a mechanical explanation for letter reversals. If this explanation is accurate, then a very simple treatment for dyslexia can be derived.

Evidence already exists that the human eye focuses by the action of the six extra-ocular muscles and that, with proper visual retraining, patients without known eye deformities can see at least as well without eyeglasses as they did with them. The debate as to how the eye focuses is strong; I cannot resolve it here. Note, however, that a simple test is likely to convince you that the extra-ocular muscles are, anatomically, able to distort the shape of the eye so as to enable it to focus.

Place your right index finger on the rightmost corner of your right upper eyelid. Look to the left. Gently press your eyelid. You will see a dot in the far left of your visual field. You can induce similar dots by pressing the leftmost corner of your left eyelid and looking right, and even by pressing the medial corners of the eyelids while looking away from your finger. The significance of these dots is that you have pressed, indirectly, the sclera of your eye sufficiently to dent it and stimulate the retina to signal that it received light. Therefore, the sclera of the eye is not rigid.

This demonstration does not conform to the prospective studies and statistical analyses demanded by organized medicine. But it works.

The six extraocular muscles are the recti and the obliques. The recti move the eyes up, down, medial, or lateral. The obliques, if they contract at the same time, pull the eye forward and compress it against the medial rectus, elongating it. If they contract not at the same time, then the eye rotates. They apparently contract together or not at all.

If the eyes focus with the extraocular muscles, then they, focus automatically by getting feedback from what is looked at. For this feedback to occur, there must be a constant fine-tuning of focus; what is seen will generally be in focus for a fraction of a second, then out of focus as the eye tries to focus better, then back in focus. The oblique muscles, therefore, will not be at a constant state of contraction as one object is looked at; they will tense and relax slightly.

And as they tense and relax slightly, not only will the eye change length, but also the fovea will move: medially as the oblique muscles contract, and laterally as they relax.

If the fovea moves to the right and the brain does not compensate, then the gaze will shift to the left and everything seen will seem to move to the right. Similarly if the fovea moves to the left.
The oblique muscles, as they contract and relax, seem to do so alternately: as they contract slightly in the left eye, they relax in the right eye, and vice versa. Therefore, the foveas move in synchrony. No diplopia occurs; objects seem to move slightly left and right if viewed by someone who has good vision and does not need eyeglasses.

Ideally, the brain compensates for this slight motion, which is not very noticeable except, for example, while aiming a firearm. Skilled emmetropic marksmen know of the need to compensate for apparent motion as they look through their gunsights.

Now consider a small child who is trying to read. He looks at a letter while his right obliques are contracting and his left obliques are relaxing. His foveas are moving to the left; what he sees is momentarily apparently moving to the left. He sees the first letter of a word and looks slightly to the right of that letter--or so he thinks. Maybe he does not compensate for the focusing of the obliques and looks too far to the right, seeing the third letter of the word and thinking it is the second. Now the right obliques start to relax and the left obliques start to contract. What he sees is apparently moving to the right. Perhaps he does not compensate for that fact when he looks at what he thinks is the third letter, so he sees the second and thinks it is the third.

If this slow oscillation of the visual field is not understood by the teacher or by the student, then letter reversals can occur and great confusion and frustration can result.

This theory can be tested. If true, there is a negative correlation between nearsightedness and letter reversals. Nearsighted people who wear corrective lenses have to keep their oblique muscles tensed; the feedback mechanism for the emmetropic eye does not seem to occur. And without the oscillations of the oblique muscles, letter reversals from this mechanism will not occur.

Another test is to try to teach people afflicted with letter-reversal habits to read letters oriented vertically, instead of horizontally. This theory explains letter reversals in a horizontal and not vertical direction. If it is correct, then vertical letter reversals will be rare and the concept of learning to read letters in the correct sequence can be taught without susceptibility to a letter-reversal mechanism that permits only horizontal reversals. I have not encountered any such studies when doing Internet searches.

The theory is supported by the observation that the moon, for example, looks smaller if it is overhead than if it is near the horizon. The difference in size is an optical illusion, as has been verified by photographs. If the eye is looking upward and is not rigid, then its weight will tend to compress it in an anterior-posterior direction, shortening it. Its weight will not tend to shorten it if it looks in a horizontal direction. As the eye shortens, what it sees looks smaller; conversely as the eye lengthens what it sees looks bigger. Simple inspection and study of a camera, a standard lens, and a telephoto lens may be helpful in understanding this principle.

Why do some people accidentally reverse letters and others do not? I cannot answer that question; recent research with neurotransmitters may solve the problem. Meanwhile, my theory suggests that teaching letter-reversing students to read vertically and later weaning them to horizontal reading is a reasonable protocol and that the theory that the eye focuses by extraocular muscles is important and relevant. My hope is that the theory will be tested and that, if verified, suitable remedial instruction in reading can be derived and possibly visual retraining can be offered to all.

Respectfully submitted to the scientific and education communities
Edward J. Harshman MD