The progression of corrected myopia

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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...

“…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].…”

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Detecting the effect of under-correcting myopia

Medina

2015

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Refractive correction and myopia progression

Galvis

Tello

Blanco

et al. 2015

We read with interest the article on the progression of corrected myopia by Medina [1]. His study was based on a feedback system prediction, and analysis of refractive data of 13 continuously corrected myopic eyes followed from 4-9 years from the time of their first correction. The author concluded that delaying the correction of myopia until visual acuity is substantially compromised is indicated and that such deferment will slow the myopia linear advance. The topic of prescribing undercorrection or leaving low myopia uncorrected is not new. Fuchs in 1899 advised to order glasses just for distance in low degrees of myopia (up to 2.00 D) and perform near-vision task without glasses, and for higher errors he recommended undercorrection [2].Until 2005, several retrospective and prospective trials performed over a period of 40 years by different authors had suggested that undercorrection or discontinuous wear of myopic correction might slow myopia progression. On the other hand, it has been suggested that a blurred retinal image, as a result of undercorrection or no correction, might accelerate the progression of myopia based on the form deprivation myopia model [3][4][5]. In accordance with that possibility, two prospective studies failed to show any beneficial effect of undercorrection [5,6]. Chung et al. in 2002 published their results of a study on 47 subjects who were blurred by approximately +0.75 D, while 47 control subjects were fully corrected (9-14 years of age). At the end of the 24-month period, the mean progression in the undercorrected group was −1.00 D, while in the fully corrected group it was −0.77 D. Undercorrection also produced more rapid ocular axial elongation [5]. Adler et al. studied 48 myopic children (6-15 years of age) assigned to fully correction (n = 23) or undercorrection, blurred by +0.50 D (n=25), over an 18-month period. In 2006 they published their results showing that undercorrection did not slow myopic progression, and rather produced a slight but not statistically significant increase in myopic progression over the 18-month period equal to 0.17 D, compared to full correction [6]. A recent retrospective study by Vasudevan et al. also showed results in concordance with these two clinical trials [7].A new randomized, controlled, double-blind trial, the Full correction and undercorrection of Myopia Evaluation Trial (FUMET), including 200 myopic children has recently been completed in China (2015) [4]. Although full results have not yet been published, the authors indicated that there were no significant differences in myopia progression or axial elongation between undercorrection of +0.5 D and full correction groups (Li SM, Wang NL. pers. comm., May 12, 2015).Medina indicated that according to his model, undercorrection of myopia is not enough to stop progression of myopia, and that leaving the myopia fully uncorrected is the This work did not have public or private financial support.

Effect of uncorrection versus full correction on myopia progression in 12-year-old children

Sun

et al. 2016