[The relationship between accommodative accuracy at different near-work distances and early-onset myopia].

ABSTRACT

OBJECTIVE: To observe the accommodative accuracy of children with early-onset myopia at different near-work distances, and discuss the relationship between accommodative accuracy and early-onset myopia. METHODS: This was a case-control study. Thirty-seven emmetropic children, 41 early-onset myopic children without correction, and 39 early-onset myopic children with spectacles, aged 7 to 13 years, were included. Measures of refractive errors and accommodative accuracy at four near-work distances, including 50 cm, 40 cm, 30 cm, and 20 cm, were made using the binocular fusion cross cylinder (FCC) of an automatic phoropter. RESULTS: Most candidates showed accommodative lags, including the children with emmetropia. The ratio of lags in all candidates at different near-work distances was 75.21% (50 cm), 87.18% (40 cm), 92.31% (30 cm), and 98.29% (20 cm), respectively. All accommodative accuracies became worse, and the accommodative lag ratio and values of FCC increased, along with the shortening of the distance. The difference in accommodative accuracy among groups was statistically significant at 30 cm (χ(2)=7.852, P= 0.020) and 20 cm (χ(2)=6.480, P=0.039). The values of FCC among groups were significantly different at 30 cm (F=3.626, P=0.030) and 20 cm (F=3.703, P=0.028), but not at 50 cm and 40 cm (P>0.05). In addition, the FCC values of 30 cm and 20 cm had a statistically significant difference between myopic children without correction [(1.25±0.44) D and (1.76±0.43) D] and emmetropic children [(0.95±0.52) D and (1.41±0.58) D] (P=0.012, 0.008). The correlation between diopters of myopia and accommodative accuracy at different nearwork distances was not statistically significant (P>0.05). However, the correlation between diopters of myopia and the accommodative lag value (FCC) at 20 cm was statistically significant (r=0.246, P=0.028). CONCLUSIONS: The closer the near-work distance is, the worse the accommodative accuracy is. This is more significant in early-onset myopia, especially myopia without correction, than emmetropia. Wearing spectacles may improve the threshold and sensitivity of accommodations, and the accommodative accuracy at near-work distances (<30 cm) to some extent. The poor accommodative accuracy at near-work distances may be not related to early-onset myopia, but the value of FCC (20 cm) is related to early-onset myopia. The higher the FCC value is, the higher the diopter is. (Chin J Ophthalmol, 2016, 52 520-524).