UC Berkeley

Long hours of computer work in the modern workplace are associated with visual and musculoskeletal symptoms and disorders, which are recognized by the World Health Organization as major occupational health concerns. The rising age of the workforce imposes new challenges in office ergonomics due to the changes in vision and musculoskeletal characteristics of these computer users.

To investigate the effects and mechanisms of oculomotor demands on the most common complaints associated with prolonged computer use, blurred vision, eyestrain, and irritation of the eyes, a within-subject design laboratory study with 17 young subjects was conducted. Subjective ratings of symptoms and objective static and dynamic accommodation and convergence responses were recorded during and after a 2-hour visually demanding computer task. Each subject repeated the task over 6 days using different combinations of natural and optically-modified oculomotor demands. While there was little effect of viewing distance on symptoms, an elevated static accommodation response and a reduced dynamic divergence response were found for the natural near viewing distance condition (33 cm) compared to the far viewing distance (100 cm). Optical manipulation had no effect at the far viewing distance (100 cm), whereas artificially decreasing the accommodation demand at the near viewing distance increased eyestrain. Divergence limits was identified as a factor for predicting the symptom of eyestrain.

A second within-subject, full-factorial design laboratory study with 19 young and 7 older, presbyopic subjects investigated the effects of age, font size, and reflective glare on productivity, upper body posture, and visual and upper body discomfort, in a setting where the subjects could freely adjust their posture and chair position while performing visually demanding tasks on a computer. Compared to the larger font size, the smaller fonts had significant negative effects on all outcome measures: productivity (speed and accuracy) was lower, visual and neck symptoms were higher, and viewing distance was decreased. The reduced viewing distance was primarily due to forward torso flexion (78%), followed by moving the chair forward (4%) and forward head movement (3%). Screen glare induced non-neutral upper body postures, including neck flexion, torso forward flexion, and head movement to the side. There was little effect of age and presbyopia on the study findings.

In summary, the first study demonstrated no difference in visual symptoms when viewing a computer monitor for 2 hours at 33 vs. 100 cm distance. However, there was some evidence of persistent oculomotor effects at the 33 cm distance. The second study demonstrated the benefits of a larger font size and eliminating screen glare on productivity, upper body postures, and symptoms when performing visually intensive tasks. The benefits were similarly experienced by both the younger and older computer users. The non-neutral, forward leaning postures, observed in many computer users, are likely due to font sizes that are small relative to visual acuity.