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Hans Olof Richter, Dmitry Domkin, Mikael Forsman; Ciliary muscle contraction force and trapezius muscle activity during manual tracking of visual targets. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3777.
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The general aim of our research program is to explore how eye-lens accommodation is integrated with functionality of the neck-scapular area muscles that contribute to coordination between movements of the eyes and the head for stabilization of gaze.The purpose of the present study is to correlate ciliary muscle contraction force to trapezius muscle activity during free-moving hand/arm work conditions. We hypothesize that ciliary muscle contraction force significantly influences the muscle activity in the neck/scapular region, with more contraction force leading to more musculoskeletal activity.
Twelve healthy right-handed subjects with normal or corrected to normal vision with an age of 23±3 years (Mean±SD) continuously tracked a slowly moving (5 mm/s) central target, a low contrast circle with a diameter of 5 mm, with a digital pen held in the dominant hand. The head was restrained to keep the eyes-screen distance at 40 cm (2.5 diopters). Each participant’s eye-lens accommodative response was recorded via infrared photorefraction measurements. Trapezius muscle activity was measured with bipolar surface electromyography (EMG). Precision of tracking, distance to target from the pen tip and variability around target, was computed from the pen tip and target coordinates. The force of contraction of the ciliary muscle was estimated using the photorefraction measurements and the formulae published by Fisher (1977).
The mean of the individual eye-lens accommodative responses computed over the full seven minutes tracking period equaled 2.5 diopters (1.7-3.7 diopters), which corresponded closely to the stimulus dioptric distance to the target. Stepwise linear regression analysis showed a significant effect of ciliary muscle contraction force on trapezius muscle activity on the tracking side, i.e. activity of trapezius muscle was higher in participants with greater eye-lens accommodative response. The finding was valid for the EMG and eye-lens accommodative response data averaged across seven minutes of the task, as well as for each minute.
The results support the idea that high accommodation/vergence demands during continuous eye-hand coordination may increase muscle tension and contribute to development of musculoskeletal complaints in the neck-shoulder area.
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