When it comes to seeing a computer monitor, the cervical spine/occipit move to adapt to the needs of the visual system, according to a recent New York City based investigation. Experienced office workers who use multifocal lense eyewear tend to assume a forward head posture after briefly reading text on a computer monitor while little change in horizontal head position was measured among non-multifocal lense eyewear users.
Those who wore multifocal lense eyewear also assumed a posture with statistically insignificant but measurably greater occipital extension than non-multifocal lense users.
Across both types of eyewear users, 25.8 percent complained of upper and mid back discomfort while 29 percent described low back/pelvis discomfort when performing work activities.
From a pool of college office workers, 33 volunteers were recruited and divided into two groups:
- 14 participants wore multifocal lenses (20/30 vision with bifocal, progressive, or trifocal refractive correction)
- 19 participants used non-multifocal lenses (20/30 vision without bifocal, progressive, or trifocal refractive correction – members of this group may or may not wear prescription corrective eyewear or contact lenses)
The subjects ranged in age from 35 to 75 years old with four males and 29 females. Each volunteer performed computer tasks for a minimum of three hours each work day for over one year. Exclusion criteria included:
- currently suffering from any shoulder or thoracic spine pain
- currently being treated by any health professional for a condition associated with the head or neck
- history of a spinal injury
- history of eye or back surgery within the last two years
Key anatomical landmarks (the mastoid process, lateral aspect of the acromion process, seventh cervical vertebrae and external occipital protuberance) were identified on each volunteer and marked with fluorescent paper markers.
A computer workstation was adjusted to fit each subject following the 1997 OSHA guidelines (monitor vertical height was adjusted such that the top of the screen was in the same horizontal plane as the subject’s eye; monitor was tilted downward 5º).
The participant performed an 8-minute task of reading text on the computer monitor at a speed he/she controlled. The 8-minute task was repeated three times with different text during each reading.
For each trial, digital photographs were taken prior to the start of text reading and at the 3, 5, and 8 minute marks post start of text reading. Computer software was used to measure forward head position (angle between plumb line through acromion process and line from the acromion process to the mastoid process) and occipital extension (angle between line from external occipital protuberance to mastoid process and line from mastoid process to seventh cervical vertebra). The mean value from the three trials was calculated.
For the multifocal group:
- the forward head position had a mean value of –0.86º at the start of the task and 4.0º at the end of the task
- the occipital extension position had a mean value of 55.07º at the start of the task and 44.93º at the end of the task
For the non-multifocal group
- the forward head position had a mean value of 0.4º at the start of the task and 1.2º at the end of the task
- the occipital extension position had a mean value of 48.4º at the start of the task and 45.7º at the end of the task
Study Limitations and Concerns
The authors point out that their study was limited by measuring only the postures and movements of the cervical region. Movement through the lower body regions may have influenced cervical positioning found in this study.
Further, it was cited that the subjects were tested at different time periods during the day and outside of their normal work environment. This brings up the possibility of findings being influenced by glare, lighting, fatigue and psychosocial factors.
The Bottom Line – How This Applies To Ergonomists
- When performing an office workstation ergonomic evaluation with an employee who wears multifocal lens, both the vertical and horizontal position of the monitor becomes significant to promote a neutral position of the cervical spine and reduce neck/shoulder muscle strain
- Over a relatively short time performing a reading task on a monitor, the horizontal position of the head and degree of cervical extension can change in a manner that increases strain of neck/shoulder soft tissues When performing an office workstation ergonomic evaluation with an employee who wears multifocal lens, both the vertical and horizontal position of the monitor becomes significant to promote a neutral position of the cervical spine and reduce neck/shoulder muscle strain
Article Title: The effects of multifocal refractive lenses on occipital extension and forward head posture during a visual task
Publication: Ergonomics, 50:12 2095-2103, 2007
Authors: M Becker, J Rothman, A J Nelson, R Freedland, D Garcia, L Feit, J Barth, and R Sabini
This article originally appeared in The Ergonomics Report™ on 2008-04-09.