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P. Ko, D. Li, P. Hoenig, I. Bailey, D. Rempel; Accommodation and Binocular Functions Changes and Visual Symptoms Associated With Computer Use. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2444.
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Visual symptoms such as blurred vision, eyestrain, headache, and fixational instability have been associated with prolonged viewing of computer monitors. Accommodative and fixation demands at near viewing distance are known to be one of the causes. We investigated the effects of accommodation and vergence demands on visual symptoms after prolonged text viewing on a computer monitor.
Ten 18-35 yr-old subjects with normal vision, and binocular vision functions participated in the study. A visually demanding task was performed over a two hour period under seven different viewing conditions. The oculomotor demands were modified by different viewing distances and different lens/prism combinations. The tasks were conducted over seven days and in random order. In the natural viewing conditions, the monitor was placed at three distances (33, 50, and 100 cm). In the unnatural viewing conditions, we increased the binocular accommodative demand by introducing -1D lenses or the convergence demand with 6PD BO prisms while viewing at 100 cm. We also applied +1D lenses or 6PD BI prisms to reduce the demands at 33 cm. The outcome measures included subjective symptom ratings, near point of convergence (NPC), time able to sustain fixation around NPC, and PowerRef II measures: static accommodation responses at 33cm, 40cm, 50cm, 1m and 4m, and for dynamic changes when using lens flipper (2D) and prism changes (6 PD). The measurements were obtained before the task and at 0, 30, 60, and 90 minutes after the task.
In natural viewing conditions, the recovery of symptoms occurred slower at closer viewing distances (P<0.05, RMANOVA). Under unnatural viewing conditions, a decrease in accommodative and vergence demands at 33cm produced less fatigue; however, the manipulation of the accommodative demands had different effects upon the symptom recovery than the manipulation of the vergence demands. In addition to the static measure, the dynamic responses also seemed to be associated with symptoms; for instance, viewing at 33cm with decreased accommodative demand produced a decreased accommodative amplitude during the facility test while increased demand at 100 cm produced an increased accommodative amplitude response (P<0.05, RMANOVA).
Different binocular vision demands influence symptoms and symptom recovery rate. Both static and dynamic oculomotor responses are affected after visually demanding computer tasks. The direction and the type of the effects depend both on the viewing distance and the kind of induced demand.
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