Effects of optical blur on visual performance and comfort of computer users

by Zeried, Ferial M.

Background. The study examined the effects of optical blur on the visual performance and comfort of computer workers. Since most workers have significant degrees of optical blur, the study may elucidate improved methodology for workplace comfort and function. Methods. Since young and old workers experience blur from different sources, the study incorporated two different designs. The study examined the correction of optical blur using a randomized, double-blind, placebo-controlled, crossover design. The primary outcomes of the study were visual comfort and productivity. In study one, subjects were required to be 19-35 yrs of age, have at least 0.50D uncorrected refractive error (URE) in at least one eye, use a computer for at least1-hr/day and have at least 20/40 corrected visual acuity (VA) in each eye. During two one-month study periods, subjects wore either lenses fitted for their best or habitual correction and completed 4 hours of testing. In study two, subjects were required to be 40 years of age or older with corrected VA of at least 20/40 and to require a near plus lens addition. Subjects completed a total of 4 hours of testing in ten 15-minute periods with their near plus prescription and a test pair of lenses (plano, +/-0.50 or +/-1.00D) with head free or fixed on a chin rest. Results. Analysis for the first study confirmed a relationship between the visual comfort index (VCI) and the number of eyes meeting the criteria of 0.50D URE and the ii task order (p = 0.0003, 0.0025) and suggested a trend for a similar relationship for correct comfortable work (CCW, p=0.0149). For the second study, the VCI declined by 15.4% (p = 0.0001) while total correct work (TCW) and CCW increased (36.4, 25.9%, respectively; p=0.0001, 0.0094) over the 2.5 hr work period. Analysis supported a hypothesis of a significant interaction of lens and head for VCI and CCW (p=0.0049, 0.0088, respectively) as well as a main effect for head position for TCW (p = 0.0069). Conclusion. Subjects were most comfortable and productive while working with low or absent degrees of optical blur in at least one eye. iii