To determine the distribution of accommodative amplitude (AA) in 6 to 12 year old children, examine the relationship between age, gender, refractive errors, and near point of convergence (NPC) with AA, and compare results with those calculated using Hofstetter's formula.

In a cross-sectional study in 2015, random sampling was done from urban and rural populations of Shahroud, northern Iran. Participating schoolchildren were examined for manifest, cycloplegic, and subjective refraction, as well as uncorrected and corrected visual acuity. The AA was measured with Donders’ push-up method using a ruler.

Of 6624 selected children, 5620 participated in the study, after applying the exclusion criteria, the final analyses were done on data from 5444 schoolchildren. The mean age was 9.24 ±1.71 years and 53.6% (n=2919) were boys. Mean AA was 14.44 diopters (D) [95% confidence interval (CI): 14.33-14.55] as measured in this study and 15.73 ±0.51D as calculated with Hofstetter's equation. AA significantly declined with age (coefficient: -0.18, 95% CI: -0.23 to-0.12, p <0.001). Mean AA in emmetropic, myopic, and hyperopic children was 14.31D, 17.30D, and 14.87D, respectively. Results of the multiple linear regression model showed that older age (coefficient =-0.18), living in rural areas (coefficient =-0.48), and NPC (coefficient =-0.47) inversely related with AA, and that higher AA was associated with a shift of the spherical equivalent refraction towards myopia (coefficient =-0.41).

Reduced AA with age was expected, but the differences among groups with different types of refractive error and high AA in myopic children are important findings of this study. The measured AA values in all age groups were significantly lower than values obtained from Hofstetter's equation. The results of the present study suggest that Hofstetter's formula provides inaccurate AA estimates in children, thus, the interpretation of this index requires further population-based studies in different racial and ethnic groups.