Accommodative lag under habitual seeing conditions: comparison between myopic and emmetropic children.
PURPOSE: To determine whether or not myopic children have a larger lag of accommodation than emmetropic children under natural seeing conditions. METHODS: In 61 myopic children (age, 9.5 +/- 1.3 years; spherical equivalent refractive error, -6.50 to -1.00 D), accommodative response was objectively measured while they were binocularly viewing a target at 50.5, 32.5, 20.9, or 16.0 cm (1.98-6.25 D) through fully correcting glasses. In the 33 children who habitually wore spectacles, the accommodative responses were also measured while they wore their own spectacles. As controls, 18 emmetropic children were recruited. Accommodative response gradients and lags were compared between the groups after calibration for residual refractive errors and the vertex distance of the glasses. RESULTS: With fully correcting glasses, the myopic children showed a larger mean lag of accommodation than the emmetropic children, as well as wide intersubject variation. However, when the children wore their habitual, usually undercorrecting, spectacles, accommodative lags markedly decreased, and a significant correlation was found between residual refractive errors after correcting for the spectacles and accommodative lags. Myopic children with near-point exophoria tended to show smaller lags of accommodation. CONCLUSION: Under binocular viewing conditions, myopic children when viewing the target through fully correcting glasses tend to show larger lags of accommodation than emmetropic children, but the lags of accommodation are usually reduced by their spectacle undercorrection.