Detecting the effect of under-correcting myopia

Abstract

The Letter to the Editor BRefractive correction and myopia progression^[1] (Bthe Letter^) makes some good points about the article BThe progression of corrected myopia^ [2] that the article had already addressed in part.Medina's feedback model for emmetropization predicts that correction of myopes aggravates their condition, and that delaying correction will result in less progression rate and probably a reduced myopic final level. The model also predicts that under-correcting myopia would have a small effect in reducing the progression rate.The Letter advises that there is controversy on the issue of whether under-correction of myopia will have any beneficial effect, citing four published reports [3][4][5][6] involving distance under-correction. Medina [2] cites those reports, and others, noting the conflict and suggesting experimental problems. The Letter overlooks several reports that show that undercorrection for near vision with bifocals reduces myopia progression, e.g. [7] and those cited in [2].In response to the Letter, the effect of distance undercorrection would be difficult to detect experimentally due to the small effect and the difficult experiment. Reports [3][4][5][6]8] discussed in the paragraphs below confirm the small and conflicting effect and exemplify the difficulty.Chung and Mohidin [3] showed a small (0.23 D) but significant greater rate of progression in a group of 47 children under-corrected by about 0.75 D as compared to another group of 47 children fully corrected for a period of 2 years. They paired the data in an attempt to avoid the problem of intersubject variation. However, the myopia progression rate is very variable, even for paired subjects of the same age and initial refractive error. Adler and Millodot [4] show no significant myopia progression difference between two groups of 23 fully corrected myopes and 25 myopes under-corrected by 0.50 D for a period of 18 months.Vasudevan et al.[5] found a significant positive correlation between the degree of under-correction of refractive error and the rate of myopic progression. This result is contradicted by a later study [8]. The difference in myopia progression between the groups with full correction and under-corrected by 0.5 D is less than 0.25D. See its Figure 1 (as amended [9]).Ong et al.[6] in a longitudinal study concluded that, over a period of at least 3 years, refractive shifts were not significantly different among a group of full-time wearers (n = 8) of spectacle correction and a group of non-wearers (n = 5), when the data were corrected for age effects. The non-wearers, however, developed less myopia than the fulltime lens wearers, and the difference was borderline significant when there was no Bcorrection^for age effects. The age Bcorrection^may be questionable given the large variation in progression rate and the reduced number of subjects. The natural variation in myopia progression is much larger than the effect of undercorrection.A recent study of two groups of under-corrected and fully corrected children [8] fail...

Prevention of myopia by partial correction of hyperopia: a twins study

“…Atropine users are therefore uncorrected, under corrected, or plus corrected during near vision. In either case, feedback theory predicts a reduction in the progression rate of myopia, as several investigators confirmed [25][26][27]. Chia et al results [23] also support the feedback theory explanation for the reduced progression rate.…”

To Correct or Not Correct? Actual Evidence, Controversy and the Questions That Remain Open

“…As previously discussed by Medina 2016 [ 20 ], most studies until now have used different groups of subjects (treatment vs. control). In contrast, the authors proposed to use the same subjects before and after the subjects received their full prescription.…”

Theory and Experiments. (+) Add Reading Glasses to Prevent Myopia

“…It is clear that these two opinions will not be resolved in the immediate future by experiment, theory, or practice. The normal approach used in the fact of disputed evidence and unresolved opinions is to explain both approaches to the individualallowing him to make the inal decision regarding the use of myopia avoidance techniques [1][2][3][4][14][15][16][17]29].…”

“…Hung & Ciuffreda [11], develop IRDT, incremental retinal defocus, to explain myopia during the growth phase. Medina et al [12][13][14] and Greene & Medina [15][16][17][18], use control theory to explain myopia development, solved with digital and analog computer techniques to evaluate irst-order equations. Viikari [19] and Goldschmidt [20], present comprehensive reviews of juvenile myopia, and various techniques used to control this myopia progression.…”