Vision Care: Preventing VDT Damage
Imperfect or obstructed vision can lead to ergonomic injuries among computer users, too. Computer users typically place themselves in front of their terminals in order to see their monitor screen, reference material, and keyboard. The posture they assume often is ergonomically incorrect. Health and safety professionals should consider workers' vision when performing workstation evaluations to offset eye strain as well as other ergonomic injuries.
Vision questionnaireHere at Lawrence Livermore National Laboratory (LLNL) Occupational Vision Clinic, an optometrist trains the industrial safety engineer to evaluate VDT workers. The industrial safety engineer is taught to take several measurements during workstation evaluations, including: distance from a worker's eyes to the terminal screen, document holder, and home row of the keyboard; size of print at various distances; distance from the eyes to the floor; and the distance from the top of the VDT screen to the floor .
A vision questionnaire is used to record these critical distances and to observe the head position, and note what type of eyewear the worker uses. Other symptoms, including headache, double vision, burning eyes, blurred vision, itching eyes, tired eyes, neckache, backache, lighting and glare problems, and other environmental concerns, are also noted. At the time of the evaluation, the user is instructed in maintaining proper ergonomic posture.
Once the vision questionnaire is complete, the user takes this form to their personal eye doctor to get an eyeglass prescription for the distances noted on the questionnaire. After the eye doctor completes the prescription form, the user returns the form to the Occupational Vision Clinic at LLNL for review that will consider unique workstation characteristics.
Occupational vision clinicThe Occupational Vision Clinic at LLNL was established in 1992 to address the visual demands of VDT users. The clinic simulates the visual task requirements and the environment of the user.
The clinic, often with workers' personal eye doctors, may prescribe three basic types of computer lenses:
A single vision lens, adjusted for the range of vision where the computer monitor and other visual tasks are located, is prescribed for workers who use the computer for extended periods of time, and are rarely required to view at distances.
A bifocal design is recommended when the employee's near range of vision is relatively narrow. Bifocal lenses have near focus on the lower portion of the lenses for reading and intermediate focus on the upper portion for VDT work. This type of lens permits more flexibility in the type of task being performed.
A trifocal design is recommended when the near vision requirements are the same as for bifocals, but distance is also required. Special wide-band lenses have near focus on the lower lens for close work, intermediate focus in the mid range for VDT work, and far focus on the top of the lens for distance viewing. The intermediate range is vertically wider than usually prescribed to allow for full screen viewing.
Eye strain and neck painResults of a survey conducted at LLNL associate lens wear with neckache. For instance, the prevalence of neckache among bifocal lens wearers suggests that much neck pain occurs from the need to tilt the head back to see the computer screen. Single vision, or special design bifocal, or trifocal lenses eliminate the need to crane the neck to an unnatural position in order to see the VDT screen.
This research emphasizes the importance of clinic simulation and evaluation of users at their workstations prior to lens prescription.
The first 68 LLNL workers to be given VDT prescription lenses were asked to report their experiences of certain visual and physical symptoms as a result of working at a VDT before using the lenses, and after. Users experienced significant decreases in headache, double vision, burning eyes, blurred vision, tired eyes, neckache and backache.
A six-month follow-up of the same group revealed a dramatic change in the number of visual and physical symptoms reported after wearing VDT lenses. There was a further decrease in the number of patients reporting symptoms in almost every area of concern.
The high number of workers with prior routine optical prescriptions suggests that workers who have prior vision problems may be predisposed to symptoms when working at a VDT. Those workers who did not have routine lenses may have had visual problems that were not apparent until the patient's use of a VDT. Thus, any uncorrected visual defect or inadequate prescription may have led to worse symptoms among the respondents.
LLNL provides prescription VDT lenses- at a cost of about $60 per pair- to its workers. Aside from reducing the likelihood of ergonomic injuries, the investment is also likely to improve worker efficiency and reduce the safety risk that workers with impaired vision present. LLNL has the convenience of an on-site vision clinic to train and evaluate workers. But hiring an optometrist on an hourly contract basis is an option for other employers.
At LLNL, prescription VDT lenses have diminished visual and physical discomfort for some 300 workers. As our survey demonstrates, properly prescribed VDT lenses can benefit workers who are suffering from visual and physical symptoms of VDT use.
This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the US Government nor the University of California nor any of their employees makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the US Government of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the US Government or the University of California, and shall not be used for advertising or product endorsement purposes. Work performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-ENG-48.