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J. Bao, H. Chen, B. Drobe, E. Seow, F. Lu; Working Distance During Near Work in Emmetropic Chinese Children. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1793.
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To investigate the working distance of emmetropic Chinese children during near vision tasks, and to delineate some of the factors affecting working distance.
91 emmetropic children (age 6 to 12 yrs) were divided into three groups: group 1 (grades 1 and 2), group 2 (grades 3 and 4) and group 3 (grades 5 and 6). Accommodative responses were measured for the right eye of each subject using a Grand Seiko WV500 with the visual target (Maltese cross) 33 cm from the right eye, and near phoria was measured using the modified Thorington test. Working distances for three near tasks (writing, reading, and electronic game (Game-Boy) playing) were measured with the Polhemus Fastrak system.
Children placed their reading and writing material on a desk surface but held the electronic game. Mean working distances were 20.57±5.65cm when writing, 24.28±6.32cm when reading, and 19.31±5.21cm when playing game. Working distance increased with school grade for all three tasks. Children in group 3 showed longer working distances than the others when writing and playing game (writing: p=0.001 for group 1 vs 3, p=0.051 for group 2 vs 3; game playing: p=0.003 for group 1 vs 3, p=0.001 for group 2 vs 3). Distance variability during hand-held game playing was less than for the other tasks (p=0.001), and the Harmon distance was correlated with game-playing distance (r = 0.28, p=0.008). Although accommodative lags were large and varied greatly between subjects (0.98D ± 0.67D), lag did not correlate with near phoria or working distance.
Chinese emmetropic children work at very close distances, especially when writing and electronic game-playing. The visual distance was shortest and most stable when game-playing. Harmon distance played an important role when children work with hand held material. But accommodative lag and near phoria did not affect the working distance of emmetropic children. The relationship of working distance to reading proficiency and the induction of myopia have yet to be determined.
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