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K. M. Daum, F. M. Zeried; Effects of Different Add Powers on the Comfort and Productivity of Computer Users With Fixed or Free Head Movement. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1005.
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The purpose of this study was to examine the effect of different near add powers on the comfort and productivity of computer users with the head fixed or free to move, considering that the magnitude of an add and head movement were the most likely factors related to visual comfort and performance.
Subjects were required to be 40 years of age or older, corrected visual acuity of 20/40 or better at distance and near and, required a near plus lens addition to perform near tasks. The study design was randomized, double-blind and placebo-controlled. Subjects completed a total of 4 hours of testing divided into ten 15-minute periods (with 5 min break/trial). During each period subjects wore a trial frame with their prescription for near plus an unknown pair of lenses (plano, +/-0.50 or +/-1.00D). Subjects completed an editing task and a previously validated survey was used to assess symptoms. Head position (head free to move or fixed on a chin rest) was monitored using a video technique. The magnitude of the difference of the add from that determined for the computer was the primary independent, categorical variable in the study. All subjects completed the experiment with ten different lens pair additions-head position combinations, randomly presented in a trial frame. The study was approved by the IRB and adhered to the tenets of the Declaration of Helsinki.
A total of 36 subjects participated (6 M, 30 F; mean age 50.3 yrs, std dev 9.0, range 40 to 81 yrs). Over the work period of 2.5 hrs, the median visual symptom index declined by 19.0% (p=0.001). Analysis provided evidence that supported a hypothesis of a difference in head position as a function of the test lens addition (p=0.0001). Analysis did not provide evidence that supported a hypothesis of a difference in productivity (total correct words edited) as a function of the lens addition considering all data together or with the head fixed.
The study did not provide clear evidence that alterations in the lens addition affected the productivity of the subjects. However, substantial evidence suggested that visual comfort was affected by the lens addition and that the lens addition affected head position. Over extended periods of work, these data also suggested that productivity may decline as a function of decreased comfort. Inappropriate correction of refractive power necessary for viewing a computer monitor at 50 cm. by a minimum of +/- 0.50 D may significantly increase visual symptoms while decreasing performance and productivity.
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