Reference: HUPER/2/1 PCS/JB L86b123
Author: Drs Haylitt Retief 1985
Munich, 3-5 September 1985
Day 2 (HUPER)
Agenda Item 7 : HEALTH PROBLEMS ASSOCIATED WITH THE USE OF
VISUAL DISPLAY UNITS (VDU)
(Presented by Captain P.C. Steilberg, (Netherlands)
The revolutionary advance of information science since the seventies ran parallel with increasing automation and intro the VDU in an ever increasing number of workplaces where traditional working methods had been applied formerly. The early seventies, as it happened, also marked the beginning Of mass unemployment and the decline of world economy. It was only natural that VDU work would become an area of conflicting interests and that the abundant literature now available should come from a variety of sources including employer oriented groups, VDU designers, trade unions and professional organisations the world over.
In the following pages an attempt will be made to give a popular, short and comprehensive account of some aspects of VDU work that could be of interest to aviators. This account will be restricted te the VDU problem areas which are most often mentioned: VDU operator stress, posture problems and problems of vision. First stress and posture problems will be mentioned briefly, followed by vision which will be more thoroughly discussed.
An attempt will be made to produce an unbiased survey, largely based on available literature used as a reference.
VDU WORK AND STRESS
Stress will simply be regarded here as a word which is used in common parlance and as such has a certain intuitive meaning to the average user of words. There has been a considerable amount of research about the relationship between VDU work and stress. A survey of this research leads to the conclusion that authors find VDU increase stress and stress related symptoms in monotonous repetitive tasks. In tasks requiring a high level of qualification this relationship is sometimes thought to be absent or less obvious.
Findings are mainly based on data from questionnaires probing for evidence of evidence of anxiety, irritability, depressive states, fatigue, insomnia and gastro/intestinal troubles.
Criticism of these studies includes questions about objectivity of questionnaires and lack of comparison with control groups with exactly similar jobs but without VDU. Even if this criticism is valid, one is still struck by the tendency of researchers to conclude towards an increase in stress with use of VDU and the absence of findings linking VDU's to an increase in job-satisfaction or other positive experiences.
VDU WORK AND POSTURAL PROBLEMS
The study of postural problems related to workstations has received considerable attention in VDU working environments. The incidence of postural problems among VDU workers is very high. Pains in the back are the most frequent. Other areas are shoulders, neck, arms and hands. These complaints are sometimes accompanied by pathological disorders, mainly evident in abnormal vertebral curvatures and, to a lesser extent, in injuries in muscles and tendons.
It is more or less generally agreed that these symptoms are produced by constrained postures, provoking postural immobilization.
Postural immobilization requires a high degree of contraction of postural muscle and is an obstacle to blood circulation.
Posture is determined by many conditions of which the physical characteristics of the workplace is only one. Tasks requiring a high degree of concentration are also known to provoke constrained postures. With VDU workers constrained postures are characterised by the head and hands being more or less permanently in a fixed position, largely determined by the appropriate eye-screen distance and the location of the key-board.
VDU WORK AND PROBLEMS OF VISION
There is little doubt that reports of eye trouble (asthenopia) are more frequent with
VDU operators than in other groups.
Individuals with visual defects, however slight and even when corrected, may be affected
more.
Symptoms
In asthenopia three main categories of symptoms can be distinguished: ocular, visual and general symptoms. Feelings of pain or discomfort localised in the eye (or eyelids) are called ocular symptoms. Disturbances of normal vision are called visual symptoms. Feelings of pain or discomfort elsewhere are called general symptoms. Ocular symptoms may include sensations of hot eyes, heavy eyeballs and eventually pain, often irradiating towards the orbit or skull resulting in headache. The eyeball is sensitive to pressure applied to the eyelid.
Visual symptoms may include blurred vision, objects may look veiled, sometimes with coloured fringes . In more extreme cases double vision may occur eventually leading to giddiness and inability to concentrate. General symptoms are mainly headaches, which need not be accompanied by ocular symptoms. These headaches are mainly localised around the orbit but may irradiate to other areas. They are aggravated by the work and of ten reach a peak in the evening.
Organic causes
The main visual functions strained in VDU work are accommodation, convergence and retinal. adaptation.
Accommodation refers to changing the form of the lens when focussing on selected visual
stimuli. Convergence refers to eyeball movement towards the tip of the nose (when looking
at nearby objects). Mechanically these functions are regulated by eye musculature.
Continuous need for accommodation and/or convergence causes eye muscle fatigue, leading to
symptoms of asthenopia and loss of visual acuity. Studies have shown that after a period
of strenuous work on nearby visual stimuli distant vision becomes impaired. This is called
temporary (work-induced) myopia. A vision loss of up to ¼ diopter is not exceptional in
such cases.
Retinal adaptation is affected when large contrasts and variations in luminance occur in
the visual field. Affected retinal adaptation may also lead to increased asthenopia and a
decrease in visual acuity.
Individual susceptibility to problems of vision
A substantial number of authors find a higher frequency of visual complaints among persons with corrected vision. in one study however, complaints were more frequent among young people with uncorrected vision. Some authors found that in a number of cases vision was inadequately corrected for VDU work. Most authors seem to think that slight visual defects (which remain undetected) contribute to visual complaints of VDU operators.
It is tempting to conclude that VDU work is incompatible with defective visual function, however slight and sometimes even when corrected.
Long term effects on vision
Studies on long term effects of VDU work on vision are comparatively rare. Most authors seem to agree that there is no proof of VDU related visual problems being irreversible. However in some studies on VDU workers significant permanent deterioration of vision was found. In one recent study on VDU workers (6868 completed questionnaires) 50,4% of the subjects reported test results had shown permanent deterioration of vision over a one year period.
Criteria
To assess the nature and degree of VDU related vision problems, questionnaires have been frequently employed. Possibly more objective methods used include measurement of phenomena directly related to visual function (e.g. visual. acuity, retinal adaptation time) or, more indirectly, measurement of performance with tasks relying on adequate visual function (e.g. visual reaction time and error detection).
The need for practical and objective measures for eye fatigue has now increased as a result of (eye) rest-time demands from VDU operators the world over. Research aimed at the development of such measures has thus been prompted.
One approach stresses the significance of reversible deterioration on the visual accommodation system as objective indicator of eye fatigue and the use of laser optometry to establish this.
This technique was used on air traffic controllers at Lulea airport and deterioration in the visual accommodation system after two hours of uninterrupted work behind the radar screen could be clearly demonstrated.
OTHER HAZARDS
There are other pathological symptoms which have been described in literature in connection with VDU's. These include dermatological reactions (skin rashes) , possible effects of radiation (reported births of children with malformations) , increased frequency of eye cataracts. We feel that these local reports may relate to incidents significantly related to VDU work at a local level but generally speaking these observations seem rare (there seems to be general consensus that VDU's do not emit hazardous radiations as far as nowadays can be measured).
GENERAL RECOMMENDATIONS (VDU)
Vision
In an effort to minimize visual complaints from VDU workers, ergonomists have concentrates on the development of guidelines which essentially should lead to reduction of retinal maladaptation and eye muscle fatigue. These guidelines mainly relate to luminance (retinal adaptation factor) and positioning (accommodation/convergence factor) of the relevant visual stimuli. Manuals and other publications now exist in which these more or less proven ergonomic guidelines, also covering posture problems, have been laid down.
Posture
Ergonomic recommendations for VDU workplaces are based on workstation measurements specifying e.g. keyboard height, eye-screen distance and chair design. The need for frequent work interruptions and subsequent moving about is also stressed.
Recommended rest periods
Recommendations on rest periods (required to recover normal distant vision) vary from 10 to 15 minutes after each hour to 15 minutes after two hours, depending on the nature of the task.
These recommendations, mainly based on VDU eye fatigue research, are now made by unions, governments and company medical departments the world over.
Other recommendations can concern the maximum time a screen should be used daily. In work requiring intensive reading of the screen it is often recommended that four hours, interrupted by rest periods as mentioned earlier, should not be exceeded.
DISCUSSION
The day will come when CRT's dominate aircraft cockpits and this may well happen in our time. This poses the questions: to what extent can presently available research data on VDU's be generalised to aircraft cockpits and what is the scientific status of this research?
Generally speaking, VDU human factors research suffers from all the shortcomings that apply to human factors research. It is difficult, if not impossible, to find articles that cannot be criticised on methodological grounds. It follows that absolute scientific proof linking VDU work to health problems is lacking.
Of course this does not mean VDU work is harmless. It merely means that scientifically speaking no one really knows. One remains to be struck by the abundance of complaints from VDU workers, the many regulations now covering work interruptions and maximum time on the job and the extensive programs suggested by scientists and physicians to subject VDU workers to careful and regular eye examinations.
The question remains to what extent VDU work in general can be generalised to CRT's in aircraft cockpits. For example it is well known that the visual stimulus on cockpit CRT's is generated in a manner which essentially differs from this process in office equipment. Also, it is frequently suggested from research findings that complaints are often related to the nature of the task. Complaints seem to be more frequent in work of a simple nature and with limited operator computer dialogue. VDU work involving time spent on activity away from the screen could also be less demanding to the eyes, depending of course on the nature of this activity and its demands on visual function in some other way.
The question of generalisation remains a difficult one. However, this applies to all human research. Without generalisation this research could never be applied. One thing to remember is that the validity of generalisations can always be refuted but not without convincing arguments.
To wait for scientific proof or question the validity of generalisations could be a debatable policy when important issues are at stake. Complaints and risks relating to eyesight have always been of special interest to aviators and if minor defects in eyesight should prove to be more problematic when working With CRT's this should be a matter of immediate concern.
Slight defects of the visual functions are quite common, particularly after the age of 40, which is also the age after which most airline pilots reach maximum proficiency and represent considerable capital investments.
Emphasis on proper visual function always remained a strict aeromedical requirement since early visual identification of distant objects had traditionally seemed to be a must imposed by nature on man travelling at high speeds.
IFR/IMC emphasis in modern airline flying hardly seems to have affected these natural requirements on the job.
To have new and probably much more stringent visual requirements gradually imposed on Pilots, resulting from the introduction of artifacts replacing quite adequate traditional equipment is another matter. Professional people who must constantly meet a large variety of highly complex requirements and whose optimal proficiency is reached after decades of handling Priceless equipment cannot be made to depend on one basically simple function unless absolutely essential aspects of this function are affected beyond an obvious safety level. If the operation of VDU's indeed subjects the eyes to a strain which is incompatible with even the slightest defect in functioning of the visual organs they would not be suitable replacements for conventional aircraft instruments. To adapt medical standards to VDU work might eventually lead to a situation where most aviators over forty could find themselves grounded. This is a situation which would be too ridiculous to contemplate.
VDU's are now a mass phenomena and there is little doubt we are only at the beginning of their advance in our time. Already substantial research programs. now in progress and concentrating on possible health hazards to VDU operators, will grow in number and scope, flourishing on funds made available by competing parties with strongly conflicting interests. Though ulterior motives may not primarily be concerned with the well-being of individual operators, research results may lead to that and it is a challenging responsibility of those formally dedicated to their interests to see te it that they do. Through extrapolation aviation could benefit from this research which is essentially about work involving intense permanent visual effort and constrained (sitting) postures.
New methods such as those aiming at objective assessment of eye muscle fatigue may for example add a new dimension to the problem of recuperation. This is one reason why it is suggested that interested parties should closely follow general human factor research related to VDU work.
RECOMMENDATIONS (AVIATION)
Considering the many controversies on health hazards of VDU work it would seem that careful monitoring of aviators converting to VDU equipped flight decks is indicated. It is consequently suggested that aeromedical authorities should be approached concerning the feasibility of epidemiological studies in which pilots flying on VDU are systematically compared with pilots using conventional equipment on similar routes over a period lasting several years.
It is also suggested that if such studies should be envisaged and/or sponsored, they should be carried out following research designs meeting rigid standards of scientific methodology, which include design approval of all parties concerned before the actual study is commenced and sponsored. It is suggested that such studies should be designed in such a manner that results will provide scientific proof concerning a relationship between VDU work and health hazards or proof of the absence of such a relationship.
Considering the vital importance of the visual functions to aviators it is further suggested serious attention should be given to the question whether, pending the outcome of such studies, exposure of aviators to CRT flight instrument should be limited to periods not in excess of the times recommended for VDU workers in general.
SUMMARY
Since the beginning of large scale advance of VDU's in industry in the early seventies,
reports of health complaints by VDU workers have been a growing concern.
Problems which are most often mentioned relate to increase in operator stress, postural
problems and problems of vision.
Postural problems may lead to pains in various parts of the body, mainly the back. They are probably caused by postural immobilization. Problems of vision are (reversible) deterioration of visible function (notably of distant vision) and feelings of discomfort or pain in the eyes which may irradiate to other areas causing mainly headaches. They are most probably caused by eye muscle fatigue resulting from a prolonged need for accommodation and convergence on stimuli at close range and are also caused by affected retinal adaptation resulting from inadequate variations in luminance.
Ergonomic guidelines aim at reducing these problems through proper workplace design (e.g. eye-screen distances, chair design), direct and indirect luminance requirements and rest periods to allow for tissue recuperation. It is suggested that aviation could benefit from this VDU stimulated research wave on work requiring intense visual effort in constrained (sitting) posture. One new method (employing laser optometry) showed significant deterioration of visual function (notably distant vision) after two hours of VDU work (radar controllers).
On the basis of this and many other studies more or less generally accepted recommendations concerning rest periods have now been made to VDU workers in general. Whether these recommendations can be generalised to aviation is discussed and it is suggested that the possibility is taken into serious consideration.
It is further suggested that aeromedical authorities should be approached concerning the feasibility of epidemiological studies concerning possible pathogenic factors in VDU work on the flight deck.
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