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B. Drobe, I. Lombo, S. Marié; Working Distance in Non–Presbyopes and Progressive Lens Wearing Presbyopes . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5861.
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Working distance is important data for near vision prescription in presbyopes as it directly determines the value of the addition. Data in children have shown that working distance is task and ametropia dependent (Haro C, et al. OVS. 2000; 77 sup). The aim of the present study was to measure working distance in young adults and in presbyopes wearing progressive lenses, in order to evaluate the influence of ametropia, presbyopia and task on adults.
79 presbyopes wearing progressive lenses (ages 45 to 71, –6.62 to +4.25 D) and 29 non–presbyopes (ages 23 to 46, –5.87 to +5.37 D) performed 3 tasks: reading at a desk, writing at a desk and reading in an armchair. Working distance was continuously recorded at 10 Hz by means of a Polhemus Fastrack device for each task.
Non–presbyopes worked significantly closer for all tasks than presbyopes (348 SD 54 mm vs. 417 SD 62 mm). This difference remained significant even after data normalization by Harmon Distance (0.88 SD 0.16 vs. 1.05 SD 0.13). The writing task was performed significantly closer than the two reading tasks for both samples. Ametropia had no effect on working distance. Among presbyopic subjects, no influence of near addition value on working distance was shown.
Working distance changed significantly in adults with task and presbyopia but not with ametropia. Presbyopes worked on average at a distance (417 mm) that matched the one for which near vision power had been determined (2.5 D). Data form non–presbyopes suggests however that 3D (333 mm) would be a more natural mean distance for near work. Great interindividual variation indicates that personal postural behaviour should be taken into account for near prescription.
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