feedback theory



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Fig. 1 Emmetropization feedback process as published in 1980 [3], translated by Otis Brown, who at about the same time proposed a similar feedback system for myopia [84] where the input was average accommodation.

Fig. 2 Feedback Theory evolved in the eighties and nineties to a mathematical definition, or transfer function F(s) = 1/(ks+1). Myopia is the result of interference with emmetropization feedback. The transfer function allows the prediction of the degree of myopia in diopters in many situations. The Theory’s prediction that lenses would alter the refraction of the eye and cause myopia in particular was tested and confirmed by many experiments with animals over two decades. Confirmation with humans followed. All predictions in this paper used this transfer function.

Fig. 3 Frequency distribution showing myopic refractive errors (negative values in x axes) becoming more frequent with age. The values in x axes are vertically aligned for easy comparison. Continuous trace is the corresponding Gaussian distribution.

Fig. 4 Negative lenses, like these carrots in front of a donkey, open the feedback loop and keep myopia advancing.

Fig. 5 Refractive error (right eye spherical equivalent SE, symbols) of 13 patients right after correction of their myopia versus age and linear fit (solid lines). The myopia depression is the straight downward myopia progression that starts when myopia is first corrected. Drawn from author’s data.

Fig. 6 Evidence that negative lenses are the cause of myopia; the fall into the myopia depression. The refractions of 605 children who became myopic fitted with straight thick lines before (years 1 to 4) and after correction (years 5 to 11). Notice the abrupt change in the rate of myopia progression. The slope of the line triples from -0.18D/y to -0.54D/y after they are corrected. Their 374 fellow emmetropes (circles), subjected to the same environmental conditions maintained their refractive change indicating that corrective lenses instead of other environmental factors are the cause of myopia. If the children had not been corrected Feedback Theory can calculate that their myopia would have stabilized at an estimated average of -1.12D (broken trace). Retraced from data in [30] and [51].

Fig. 7 Actual refractive development R(t) of a child’s eye whose hyperopia was corrected by 50% from age 7 to 17 (diamonds, SE) and prediction of Feedback Theory if such correction were maintained indefinitely (continuous trace). Notice the expected negative refractive change after correction was discontinued deviating towards myopia from corrected prediction. Drawn from author’s data.

Fig. 8 Flat prediction of Feedback Theory if the child’s hyperopia had been fully corrected.

Fig. 9 Prediction if alternative treatment had been followed: the child’s hyperopia had not been corrected, he had an increased near work demand of 1 D and his myopia had been fully corrected every time it increased by 0.25 D.

Fig. 10 The Theory was put to the test to prevent myopia in a 11 year trial that culminated in 2018. These two boys in green gowns were at risk of developing myopia, but are free of myopia and glasses at graduation (upper photo) after 10 years of preventive positive lens wear (lower photos). Just as Feedback Theory predicted. See [8] and Figs. 7 to 9 for details of the trial.

Fig. 11 A candid photo faithfully illustrates Feedback Theory explanation of myopia, its progression (1), its cause (2-5), and its prevention  with positive  lenses (6-7) respectively.