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Eyes and vision

Of all the hazards associated with VDU work, visual problems are the most widespread. During the last twenty years in which VDUs have been in general use there have been several hundred studies which have confirmed the link between VDU work and the visual problems reported by users.

Numerous surveys and epidemiological studies (studies of the causes of ill-health in large groups of people) have shown that at least a quarter of all users experience visual problems as a result of their work. The percentage of workers suffering visual problems increases in proportion to the number of hours worked at the VDU. Surveys of those working more than six hours a days at the VDU have found up to 91 per cent experience visual problems.

Visual problems are higher among those doing repetitive keyboard and screen work such as data entry, than among VDU workers doing less intensive work where VDUs are used intermittently. Work involving the use of VDUs produces considerably more eyestrain than almost all other types of non-VDU work. A recent study found that the occurrence of abnormal eye function was nearly 16 times higher in VDU workers than in non-VDU workers (Ishikawa 1990).

The range of problems reported include the following:

• the sensation commonly described as 'eyestrain'
• burning or tender eyes
• reddened, watering eyes
• blurred vision or difficulty in focusing
• double vision
• grittiness, dryness or aching of the eyes
• worsening of pre-existing visual problems
• the need to get prescriptions for glasses or lenses changed more often
• changes in colour perception (eg. seeing coloured after-images after using the screen such as floating red or orange blobs, or seeing everything white tinged with pink)
• a feeling of heaviness in the eyes
• headaches just above the eyes

The extent to which individual VDU workers are likely to suffer from eye trouble will depend on a number of factors including the state of their eyes, the design of the equipment, the design of the workstation and the workplace, the nature of the work and the frequency of breaks.

How VDU work affects eyes and vision

The eye consists of specialised parts which combine to provide information which is translated by the brain into visual perception or seeing. Anything upsetting this delicate balance, such as prolonged visually demanding tasks, may cause difficulties.

VDU-eye interaction makes heavy demands on the visual system in the following ways:

Scanning the display screen requires both right to left as well as up and down movement of the eyes, compared to reading hard copy text, which requires mainly right to left movement. Studies have shown that both poor lighting and badly designed typography can lessen the efficiency of these types of movement in reading. Given the poor standard of lighting in many offices and the crudity of most VDU typefaces compared with those used in print, it is likely that these are additional causes of strain for most VDU operators.

Each time a VDU operator looks from printed text to the display screen, or around the office, the eyes are refocused by the ciliary muscles. Each time the focusing distance is changed the ciliary muscles must modify the shape of the lens to ensure a clear image.

Where the operator has to keep the eyes focused on the screen for extended periods, the muscles in the eyes can easily become overloaded.

A prolonged focusing effort can also cause eye irritation, eye strain, watering and reddening. Eyestrain is a very common cause of headaches occurring during or after completing visually demanding tasks.

Changing from looking at a dimly lit screen to a brightly lit office requires a change of pupil size by the radial and circular muscles of the iris. Because it forces them alternately to tighten and relax very rapidly, it is these muscles which are affected by flicker. At high speeds the eye does not register the flicker of a bright light, but if it flickers at less than 60 times a second (ie. has a 'refresh rate of less than 60Hz), slow enough for the eye to register it and attempt to respond, acute discomfort can be experienced. Flickering becomes a greater problem with old VDUs.

The muscles controlling pupil size are particularly likely to become stressed if there are reflected images on a screen and the operator's eyes are forced continually to focus and refocus on the reflected images and on the characters on the display.

Some reports suggest that viewing a VDU screen for repeated prolonged periods can cause short-sightedness (myopia). A recent optometrists' guide states that intensive close work such as that performed by VDU operators is frequently associated with the worsening of myopia (Grundy, Rosenthal and Seymour 1991).

Blinking is the eye's natural windscreen wiper. It stimulates tear production and washes out contaminants. Some studies have found that the blink rate goes down among VDU operators, leading to greater dryness and irritation of the eye. If the contaminants are not removed effectively by the blinking reflex then infections can result.

Workstation and workplace factors affecting vision

The workstation

The watchword for workstations is adjustability. As many features as possible should be under the direct control of the operator who should also have the opportunity to make frequent changes of posture. Where workstations are to be used by more than one person, this adjustability becomes even more crucial - it must not just cater for all the varieties of movement which one operator may wish to adopt, but must also allow for those of other workers who will be of different shapes, sizes, ages and abilities. For instance, what suits a 20-year-old, 6-foot, shortsighted man at 5pm in the winter will be very different from the adjustments appropriate for a 40-year-old 5-foot woman with long sight on a sunny morning.

Detailed recommendations on workstation design are given in Chapter 9 but key requirements are:

• the screen and keyboard should be fully adjustable separately
• the chair and table height should be adjustable
• there should be sufficient desk space for laying out of work to suit the operator
• desk and equipment surfaces should be made of materials which do not produce glare or contrast brightness with input documents
• the VDU screen should be positioned at eye level and the distance between the hard copy and the screen should not be too large. The Association of Optometrists' advice is that the source documents and other work materials should not necessarily be at the same distance as the screen as the size of hard copy text is usually smaller than the characters on the screen. The shorter the working distance, the greater the risk of developing shortsightedness (Grundy, Rosenthal and Seymour 1991). Again the critical factor is adjustability to suit the individual operator
• all VDU operators should be able, without moving from their workstation or twisting uncomfortably, to look periodically into a distance of at least 20 feet to rest tensed eye muscles
• adjustable document holders should be available

The screen

In Chapter 7 we look at screen technology and recent developments in some detail. Some key factors which affect character and symbol legibility and which in turn impact on vision include:

• character size
• the dot matrix density (the number of dots per inch making up the characters)
• brightness
• contrast
• resolution
• stability
• design
• colour and polarity (whether there are dark characters on a light background (negative polarity) or light characters on a dark background (positive polarity)
• viewing angle.

Legibility may also be affected by the age of the VDU and the effectiveness of maintenance including cleaning. A 1989 study found that blood pressure and stress levels of VDU users were increased when viewing small characters (of 4.8 x 2.6 mm) compared to viewing larger characters (5.6 x 4.8 mm) and this effect increased with the age of the user (Tanaka et al 1989). Another study found that poor screen legibility caused increased rates of eye discomfort (Collins et al 1990).

Lighting

A great deal of often highly technical writing has been produced about the most appropriate lighting for VDU work. It is a complex subject partly because individual lighting requirements vary enormously.

Furthermore, VDU work is rarely the only visual activity going on in any particular area. Most VDU workers must also refer to documents, use the telephone, check print-outs and carry out a variety of other tasks, all of which require different types and levels of lighting. Most solutions are therefore likely to be a compromise of some sort.

The two key principles to remember here are that lighting should be as individually adjustable as possible without interfering with the lighting of neighbouring workers.

The objective when selecting lighting for office environments where VDUs are in use is to provide adequate levels of background illumination and contrast with the screen, while at the same time avoiding glare and reflection on the screen.

Downlighters or direct lighting should always be fitted with diffusers to control the light distribution and to provide even brightness. As fluorescent lights (without diffusers) have large exposed areas they may dazzle your eyes and affect your capacity to see clearly - so it is particularly important that they are fitted with adequate, preferably opaque, diffusers (London Hazards Centre 1987).

Well planned uplighting is particularly suitable for VDU work as it provides indirect lighting reflected back from the ceiling which minimises reflections on the screen. However, use of uplighters is not recommended if the floor to ceiling height is less than 2.5 metres (Grundy, Rosenthal and Seymour 1991).

Glare

Glare can be caused by direct light or reflections and may lead to eyestrain, headaches and tiredness. As well as glare from artificial lighting, light from windows is a frequent cause of glare. The following can help to reduce glare:

• fitting adjustable shades or blinds to windows
• arranging VDUs so that neither operators nor screens are facing an unscreened window
• where fluorescent lights are used, make sure that the tubes are viewed end on when operators are sitting at their workstation
• covering direct light sources with a diffuser
• Use low reflecting furnishing and decorating materials

Job design factors affecting vision

The structure, duration, demands, pace, breaks and task variation of the job all influence visual stress. Frequently, the introduction of VDUs to a workplace can create a high demand, low control situation for the workers required to use them.

A consistent finding of studies of VDU users is that vision-related problems are higher among operators doing repetitive keyboard and screen work than among those doing more creative question and answer work suggesting that the intensity and repetitiveness of the work are important factors. Full-time workers suffer noticeably more than part-timers. Studies have also shown that eyestrain becomes worse in direct proportion to the amount of time spent each day at a VDU.

Work which requires operators to stay in the same position working on a repetitive task for long periods without rest invariably causes visual strain and tiredness.

Wherever possible the frequency, timing and duration of rest breaks away from the screen should be under the control of the individual worker. Studies have shown that to be effective, rest breaks should be taken before the onset of fatigue. The Association of Optometrists recommends that in addition to hourly breaks of several minutes, every 15 minutes or so the eyes should be relaxed by looking away from the screen to objects at a greater distance.

The Hazards Centre advises workers wherever possible to negotiate for job design that includes several different types of work and to avoid job agreements requiring workers to work for most or all of their day at a VDU.

Research commissioned by the HSE from the University of Nottingham supports this advice - they found that to be effective in reducing fatigue and stress, breaks should be taken away from the VDU, and should not involve transfer to an equally repetitive task (Cox, cited in NALGO Safety Representative June 1991).

During the drafting of the EC's directive on VDU work - implemented in the UK as the Health and Safety (Display Screen Equipment) Regulations 1992 - many unions and hazards campaigning organisations attempted to have daily time limits for VDU work included (London Hazards Centre 1992). However, resistance by the HSE and the CBI has meant that the DSE Regulations do not specify time limits and the most that is required is periodical interruptions of work at the screen.

Key points from the guidance to the regulations include the following:

Eye and eyesight testing

It is estimated that as many as one in three of the workforce has uncorrected or insufficiently corrected vision defects. Many of those with vision defects will only become aware of them once they start to do visually demanding work such as VDU work.

To ensure that VDU workers do not suffer from the pain, headaches and blurred vision which may result from working at a VDU with an uncorrected vision defect, all workers should, if they wish, have free eye and eyesight testing.

UK trade unions have campaigned for many years for eye testing for VDU workers and now, despite resistance from industry and the statutory authorities, the new DSE Regulations, which include specific requirements for testing, have come into force. The Regulations cover both eye examinations and sight tests.

The regulations state that employers of both existing VDU users and new users:

Health and safety campaigners have long been wary of any form of employment or pre-employment screening which is used to exclude or discriminate against particular groups of workers. However, in this case, the regulations make clear that the purpose of the tests is to identify vision defects in order to correct or remedy them and not to exclude workers on the grounds of those vision defects.

When should the tests be carried out?

The regulations state that for existing users the test should be

and for new users, or employees about to become users the test should be

What type of tests?

The regulations are intended to implement the European Directive Minimum safety and health requirements for work with display screen equipment, which makes specific the right to eye and eyesight tests.

Although the DSE Regulations also specify this right, in its guidance to the regulations, the Health and Safety Executive suggests a convenient watering down of the provision for employers - that in the first instance, vision screening tests, (which are far more superficial than full sight tests) may be offered as a means of identifying those who need a full sight test (although those users who request a full sight test will be entitled to one).

Since it is unlikely that the majority of VDU users will have in-depth knowledge of the distinction between eye examinations, vision screening and full sight tests, this 'guidance' may lead to many VDU workers being deprived of their rights.

[pic: bolle advert with caption: This advert for vision testing equipment illustrates the importance of taking up your rights to eyesight testing by independent, qualified practitioners - the purchase by employers of a piece of electronic equipment to do the job to 'save them time and money' does not fulfil the requirements of the regulations.]

How often should the test be carried out?

In its original Consultative document on the Directive, the HSE proposed restricting the right to repeat tests to once every ten years. Fortunately the outcry that this provoked led to a reinstatement, as intended in the original directive, of the right to re-testing at regular intervals.

The regulations now specify

The British College of Optometrists' Statement of Good Practice for work with Display Screen Equipment advises that reports on eye examinations and sight tests should include recommendations on the frequency of re-examination.

The report should also state whether or not corrective appliances (ie glasses or contact lenses) are needed for VDU work and as well as making the report to the employer, the optometrist should provide the employee with a copy. Details of the prescription should only be included in the employer's report if the employee gives permission.

The Statement of Good Practice goes on to remind practitioners:

Confidentiality of clinical information about the employee must be maintained at all times and clinical information should only be divulged to an employer if it is relevant to the employee's work at the VDU and only with the patient's consent (British College of Optometrists 1992).

Who is a 'competent' person?

The guidance to the regulations makes it quite clear that employers must offer employees testing by registered ophthalmic opticians (optometrists) or registered medical practitioners with suitable ophthalmic qualifications.

Unfortunately, this guidance is somewhat undermined by the section on vision screening tests (see also page 00) which suggests that those conducting these tests need only have a basic knowledge of the eye and be competent in the operation of the instrument or test. This is the type of eye testing offered by many companies with occupational health facilities. However the Association of Optometrists recommends that eye and eyesight testing should be done by the employee's own optometrist, thereby ensuring that eye care is provided by the practitioner of the employee's choice.

The Association goes on to point out that this arrangement:

offers the employee a professional opinion independent of the management or any management nominee and has proved valuable in increasing employee confidence. [sic] (Grundy, Rosenthal and Seymour 1991).

Our advice is that workers should take up their entitlement to a full eye and sight test and not to be fobbed off with on-site vision screening by unqualified persons.

Corrective appliances

If the eye and sight tests show that an employee needs glasses (corrective appliances) specifically to correct vision defects at the viewing distance of the VDU then the employer must provide them (Regulation 5 (5)).

Unfortunately, the regulations limit the employer's responsibility to providing glasses only when:

The British College of Optometrists interprets the Regulation to mean that free glasses should only be provided to those with special needs related to their use of a VDU as part of their employment.

Clearly, there is scope in the regulations for different interpretations of what vision defects will affect employee's ability to do VDU work, and therefore qualify for 'special corrective appliances'. This is likely to lead to inconsistent provision to those who really need glasses to do the work, and who otherwise would not have had to buy them, and the meanness of the regulations in this respect is one of their major flaws.

Who pays for eye tests and glasses?

Where special glasses for VDU work have been prescribed, the employer only has to pay for the basic cost ie. lenses and frames which adequately do the job of correcting the vision defect which affects VDU work. If the employee wants special frames or glasses which perform other functions, then the employer must still pay the basic cost, but the employee would have to make up the difference.

Long-term eye damage, epilepsy and cataracts

Current statutory advice emphasises that eye and other health problems associated with VDUs are not caused by the VDUs themselves, but from the way in which they are used. (HSE 1992).

Whilst there are undoubtedly many factors about the way in which VDUs are used that affect workers' health, there remain some concerns about the technology itself, which may be responsible for some ill-health linked to VDU work, and which is discussed in more detail in chapter 7. In particular, there have been some studies which have suggested that:

• work with VDUs may increase the risk of seizure in those suffering from photosensitive epilepsy
• there may be an increased risk of developing cataracts
• work with VDUs may cause permanent deterioration of eyesight

Official guidance assures us that extensive research has shown that VDUs will not cause disease or permanent damage to eyes. However, the guidance fails to explain the findings of several experts that some VDU workers may be at risk of more serious long-term damage than eyestrain which can be corrected by appropriate workstation and workplace design.

For example, a clinical professor of optometry at the University of California found in a recent study of 150 VDU operators who used VDUs for an average of six hours a day over four year that two thirds of them had difficulty focusing their eyes (Sheedy, cited in Brodeur 1989). Professor Sheedy reported that it was possible that VDUs might be causing some breakdown in the eye focusing mechanism.

Japanese scientists have investigated the possibility that visual disorders associated with VDU use are caused by an effect on the central nervous system. In a study published in 1991, they found that VDU work was associated with impairment of the visual nervous system function, and that this finding was increased the greater the number of years the operator had been working with VDUs (Murata et al 1991).

Dr Ann Silk, a contact lens practitioner, reported to the first UK conference on electro-medicine in May 1990 that she had observed several chronic changes (including changes in the lens which can produce a significant reduction in vision - similar to that produced by cataracts) in the eyes of VDU workers and had also found that exposure to VDU electromagnetic fields had changed the surfaces of gas permeable contact lenses (Electromagnetics News May/June 1990).

It is clear that as long as health and safety legislation is based on standards that will not impose excessive 'burdens' on industry, rather than on prevention of occupational ill-health, VDUs, as with other workplace equipment and materials, will be given the benefit of the doubt.