Effects of VDT monitor placement and single versus bifocal glasses on somatic discomfort and postural profiles in data entry tasks.

A study was conducted to determine the effects of VDT monitor positions and the use of single vision versus bifocal glasses on somatic elements in the data entry task. Eight male subjects performed data entry using a word processor in eight half-hour sessions with the four different monitor placements, i.e. "eye-level", "shoulder-level-front", "shoulder-level-side", and "sunken-level", wearing the two types of glasses. A subjective discomfort rating questionnaire covering 12 somatic elements was completed by the subject after each session. The head inclination and angle of gaze to the monitor were measured with a goniometer. The results revealed that the somatic elements which were affected significantly by the placement of the VDT monitor and the type of glasses were discomfort in the neck and back regions and eyestrain, respectively. The neck-back discomfort scores were highest at the "eye-level", lowest at the "sunken-level", and intermediate at the "shoulder-level-side" position. The "shoulder-level-front" position was not significantly different in the discomfort from other three positions. The eyestrain was significantly greater with the bifocal than with the single vision glasses. The lower the monitor was placed, the more forward was the head and gaze inclined. The head was inclined less forward, or even more backward, and the gaze was inclined more forward, with the bifocal than with the single vision glasses. As a conclusion, the VDT operators were advised to avoid the "eye-level" and "shoulder-level-side" positions and to prefer the "sunken-level" and "shoulder-level-front" positions as the first and second best choices, respectively. The preference becomes more critical for the wearers of bifocal glasses that suffer from postural constraints in viewing.