Emmetropization: A foisted fallacy by Bezalel Schendowich, OD

Bezalel SchendowichEmmetropization is the process by which the refraction of the anterior ocular segment and the axial length of the eye tend to balance each other to produce emmetropia. This is a nice definition. It has been contributed by “The Free Dictionary by Farlex”. The definition deals with anatomical and physiological changes which statistically seem to occur quite frequently and naturally across the spectrum of creation.

My problem with a fairly natural process is what the eye care profession has done with it. The prescription of glasses for hyperopic children, for instance, has suffered greatly by the misapplication of the various observations concerned with emmetropization. Somehow was born the theory that reducing the plus lens refraction for prescription would somehow speed-up the reduction of the amount of plus the child’s eye required. The problem with this is that the concept is exactly parallel to over-minusing a myope. That certainly does not help the nearsighted child become less myopic; in fact, under-plusing the hyperope might just speed up his myopization – who is to predict that his loss of plus will stop at plano?

Much work, investigation manpower, time, and funds have been expended over the decades seeking the truth of myopic progression and in exploration of the various theories of emmetropization. I believe that many of the results published simply show the difficulty involved in acquiring accurate refractive data from newborns and children of all ages. Purportedly, the gold standard for refractive accuracy in children is the cycloplegic examination under anesthesia. To put every child at every examination to sleep is untenable, expensive, and risky. Alternatively, examining an awake infant suffers from poorly defined depth of cycloplegia; poor retinoscopic image through the dilated pupil; and, mostly a gross lack of cooperation in the large percentage of children.

As children grow and more emphasis is placed on the subjective result, results become tainted by the patient interpreting “better” as smaller, crisper and darker. In this way a more minus or less plus result is obtained.

Studies of consecutive refraction show a drop in myopia by the end of the third and beginning of the fourth decades. This can be interpreted as a failing of over-accommodation and an approach to “correct” correction. The same thing is seen as hyperopia becomes more manifest in the same age-group. Thus, the classic case of the 35 year old previously uncorrected patient who presents with poor distance vision and who improves dramatically with plus; but, needs pre-maturely a relatively high reading addition to attain normal near acuity. She will gradually manifest her hyperopia and her add will approach an age-related normal value. In her case emmetropization was merely a complicated word for visual penalization through her early adult years.

As refractionists, optometrists, and other sorts of eye care providers our goal ought to be the prescription of the most accurate, optimal prescription so that our patients can attain comfortable, efficient, binocular visual acuity. To take a child with apparently straight eyes and arbitrarily reduce the plus refraction found by two or three diopters in the name of some mythical ‘god of emmetropia’ really makes no sense. More to the point would be an accurate dynamic result, or simply using the rule of thumb founded in the experience of our ancestors of reducing the cycloplegic result by a diopter more or less. Taking off too much has been shown to throw a visual system that was tottering accommodatively into clear full blown esotropia.

The best advice in the prescription of refractive result is to go easy; be conservative; respect all aspects of the visual system; and, especially for children invoke the rule of follow-up and the right to up-grade the prescription as necessary. We must remember that the visual system is plastic; responsive to environmental, physiological and psychological stimuli; and that our result at one visit may well not be reflected in subsequent visits.

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