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Emma Chu, Jane Gwiazda; The effect of light intensity and accommodation on short-term axial length changes in myopes and emmetropes. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5699. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effect of light intensity and accommodation on short-term axial length changes in myopic and emmetropic young adults after reading.
23 young adults (mean age=23.8 years), 16 myopes (mean spherical equivalent refraction [SER]=-3.63D) and 7 emmetropes (mean SER=+0.14D), participated in the study. Measurements of refractive error and accommodation (Grand-Seiko Autorefractor) were taken. After baseline measurements of axial length (AL) (Haag-Streit Lenstar), subjects engaged in 15 min of reading standardized text at 33 cm under 4 randomly assigned conditions: dim incandescent lighting (8-15 lux) wearing distance best corrected SER (DimSER), dim lighting wearing distance SER with a +2.00D add (DimAdd), bright fluorescent lighting (8000-10,000 lux) wearing distance SER (BrightSER), and bright lighting wearing distance SER with a +2.00D add (BrightAdd). AL measurements were recorded immediately after each condition; subjects then took a 5 min break before the next condition. The primary outcome was change in AL with respect to baseline. Repeated measures ANOVA was used to compare AL change with respect to baseline among the 4 conditions and between the two refractive groups.
Overall, there was no difference in the AL change with respect to baseline across the 4 conditions (p=0.40). However, there was a significant refractive group difference in mean AL change from baseline; overall, the AL of myopes increased, while the AL of emmetropes decreased (p=0.013). Specifically, paired t-tests showed a significant difference in AL change between the myopes (mean+/-SD= +2.6um, +/-0.07) and emmetropes ( -10.3um +/-0.12), p=0.005, in the BrightAdd condition. The DimSER also showed a significant difference in AL change between myopes ( +5.3um +/-0.14) and emmetropes ( -6.9um +/-0.04), p=0.018. Refractive group differences in AL change in the BrightSER and DimAdd conditions were in the same direction and marginally significant, p=0.07 and p=0.09, respectively.
Our results show that shortly after 15 min of reading, the axial length of myopes increased compared to baseline, while the axial length of emmetropes decreased, similar to a recent study (Woodman et al, 2012). Furthermore, changes in AL did not vary under different lighting conditions, suggesting that, contrary to popular belief, reading in dim light may not increase the risk of developing myopia.
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