Viewing distance variation and related ophthalmological changes in office activities with and without VDUs

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Abstract
This experimental study was conducted on 14 volunteer female clerks to measure viewing distance variation and related ophthalmological changes in office activities with (session 1) and without (session 2) VDU. A video camera connected to an electronic elaborator was used to determine eye-screen distance of the VDU operators during the task. Before and after each of the two work sessions far refraction, far phorias, near point of accommodation (APP), and fusional convergence were measured. Blinking rate of each subject was measured by a transducer only during the ‘VDU session’. The objective measurements of the eye-screen distance, whose range was between 48·42 and 65·33 cm, allowed a precise quantification of the occupational visual load during session I. The accommodation was about 1·5–2 D on average and the fusional convergence 10–13 Δ on average. The symptomatology shows a number or disturbances in session 1 (71·4%) clearly higher than in session 2 (35·7%). The study of refraction before and after the task has shown a slight excess of accommodation compared to the theoretical value in both sessions, more marked in session 1. The APP shows no statistical significative variation. A tendency lo exophoria was registered at the beginning and at the end of the trial and the fusional convergence clearly decreased, especially in the first session.