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J. Kim; Inter-Ocular Myopic Refractive Error Changes With Lag of Accommodation. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1007.
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Many myopia studies using animals have reported that hyperopic retinal defocus causes myopia. Other studies correlating myopia with accommodation have also suggested that myopic eyes have higher hyperopic accommodative errors at near, and that sustained accommodation errors may cause and increase myopia. The purpose of this study is to investigate the relationship between hyperopic retinal defocus, as related to accommodative lag, and increasing myopia.
25 children (12 males, 13 females) aged between 5 years 4 months and 14 years 8 months (mean 9.45 years) participated in the study. Distance refractive errors were measured using an autorefractor (N-Vision, Shin Nippon). Accommodative lag (AL) was measured by the monocular estimation method at 40cm under habitual refractive error correction with glasses. Subjects were divided into two groups: inter-ocular difference in AL (n = 13) and same AL in the two eyes (n = 12). Spherical refractive errors (SRE) were followed for 28 ± 15 months (10 to 54 months).
In subjects with the same AL in both eyes, myopic SRE increased by more than 1.50D, from -0.72 ± 0.61D to -2.23±1.46D, in the less myopic eye (LME; t-test, p < 0.001), and by1.14D, from -2.48 ± 0.74D to -3.61 ± 0.92D, in the more myopic eye (MME; t-test, p < 0.05). Although the increase in SRE for the LME was 0.48D greater than for the MME, this difference did not reach statistical significance (t-test, p>0.05). In subjects with different AL in right and left eyes, AL averaged 0.94 ± 0.56D for the higher accommodative lag eyes (HALE), and 0.02 ± 0.47D for the lower accommodative lag eyes (LALE; t-test, p < 0.0001). SRE changed by 0.48D, from +0.11 ± 0.65D to -0.37 ± 0.98D (t-test, p < 0.05), for the HALE and as much as 1.07D, from -0.78 ± 0.85D to -1.85 ± 1.06D (t-test, p < 0.0001), for the LALE. The increase in myopic SRE for the LALE was 0.59D higher than for the HALE (t-test, p < 0.001).
Higher accommodative lag means more intermittent hyperopic retinal defocus. This study showed that the HALE demonstrated less increase in myopia than the LALE. This result is inconsistent with suggestions that hyperopic retinal defocus is a major factor underlying increasing myopia.
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