Blind spot

Employers too often neglect one of their most valuable tools
– their workers’ eyes. But failing to undertake assessments could cost both
them and their employees dear.  By Dr
Janet Voke


Many industries rely heavily on the vision of their employees
to make critical decisions, yet protective measures are often applied
haphazardly and the effect of industrial conditions and advancing age on eyes
are little considered.


Failing sight in older age poses a greater risk of accidents
and reduced efficiency. At work these potential problems can bring significant
risks and undermine the confidence of employee and management.


Eye disease can greatly affect vision and visual
performance. The common diseases of glaucoma and cataract reduce a significant
proportion of the over-40s each year to partial sight. Glare is also noticed
much more with advancing age and colour discrimination deteriorates from early
middle age. More light is needed on the job as the lens builds up cataract and
the nerve layer of the retina at the back of the eye is reduced.


Lighting levels


Although modern trends tend to favour dimly-lit
environments, adequate illumination must be provided for tasks. With advancing
years this means more light at work, both as ambient illumination and in the
form of local lighting at the workstation.


At 20 years of age the average pupil diameter in the light
is 3mm, and in the dark 7mm. For a 60 year old, these values are 2.5mm and
5.5mm, so that less light is physically able to enter the window of the human


From these values it is recommended that twice as much light
is needed at the age of 40 compared with 20 years, and three times as much at
60 years. These may seem alarming figures, but they are realistic. For every 13
years increase in age, the intensity of illumination has to be doubled in order
for a small light source to be visible to a dark-adapted eye. The muscles that
control the pupil aperture through the iris near the front of the eye weaken
with age and pupils become smaller.


At the back of the eye yellow pigment builds up in the
central part of the retina making blue vision more of a problem. A tendency
towards yellowing and browning of the eye lens in the middle of the eye – known
as cataract – makes vision less sharp with blues and greens particularly
compromised as these wavelengths are absorbed.


Cataract affects us all to some degree but for diabetics and
those who have had long-term occupational exposure to infra-red or ultra-violet
radiation the risk is even higher.


A relatively simple operation now replaces the opaque lens
with a clear perspex implant and vision is restored.




The discomfort, and even disability, that arises from
excessive illumination in the form of glare is much more troublesome to those
over 40. Glare is largely produced by the scattering of light within the eye
tissue, so that the increased opacity of the older eye lens will enhance this
effect and contribute to the glare. This phenomenon is also noticed at night
and is the reason older people are reluctant to drive in the dark.


Although factory lighting has improved greatly in recent
years, when operators work in dark rooms the problem of glare can easily arise.
Blinds should be carefully situated in workplaces and operators should not
hesitate to use them – this is particularly important for users of visual
display units.


EU regulations require all workstations to be assessed for
potential risk. Visual fatigue is the greatest problem and those over 40 would
be expected to complain most frequently.


Table lamps on desks can add to background lighting and up lighters
on ceiling lights can help. Factory corridors, stairways and passages should be
well lit to assist older employees. This is particularly important in locations
where there will otherwise be sharp changes in lighting levels, for with
advancing age ability to adapt to darkness also declines.


Colour changes


A gradual development of normal colour perception from birth
towards youth and a gradual decline from between 30 and 40 are widely reported.
Generally, a red-green deterioration is believed to begin around 55 to 60
years, but a more marked loss in blue-green discrimination accompanies it from
an earlier age – even from the third decade of life. Such changes can be
detected by the more sensitive standard tests for colour blindness.


Blue-greens, blues and violets or mauves can cause
difficulty to the elderly, and in matching pale colours – particularly whites.
The industrial consequences of these changes can be significant, particularly
in sectors such as textiles and dyeing where visual colour assessment is


Employers have, in general, been slow to consider these
changes in colour perception. This is surprising when one considers the
attention  given to standardisation of
illuminants for industrial colour appraisal in recent years. Since the age
difference of a colour matcher is similar to putting yellow filter in front of
the eye and thus changing the colour temperature of the light source, these
changes must not be neglected.


Industrial standardisation of lighting is therefore useless
unless there is some standardisation of the observers too, and it is highly
desirable that those under 40 are given the visual colour matching
responsibilities in industry.


Forms of colour blindness can arise from general diseases
including diabetes, chronic liver condition, multiple sclerosis, anaemia,
severe vascular and cardio-vascular disease and vitamin deficiencies, all of
which affect the older worker more frequently than the young.


Many of these colour vision problems arise suddenly and
involve a range of potential colour confusions. They are prone to increase in
intensity and undermine any industrial visual colour discrimination task.
Unlike the inherited types of colour blindness, these acquired problems are
usually very erratic.




The range of drugs available today can also threaten the
visual efficiency of staff through side-effects which may dim vision or cause
significant disturbances.


Chemicals such as carbon disulphide, ethyl alcohol, carbon
tetrachloride, ethyl glycol, mercury, manganese and lead and components of
explosives can all change colour perception permanently. Often this occurs in
only one eye or in one part of the visual field and sometimes temporarily.


Antibiotics, antibacterial agents, heart stimulants,
anti-depressive drugs and anti-arthritic drugs along with medication used to
control high blood pressure and epilepsy can significantly alter vision,
increasing the risk of accidents.




General complaints of headaches, eye-strain, fatigue and
watering and stinging eyes are often made by operators required to work at
visual tasks for extended periods. The display and retrieval of numerical and
graphical data on a monitor can present problems to the older worker who has
poor tolerance of visual discomfort. Eyes tend to water more with advancing age
as tear flow is poorly controlled and this can lead to blurring when
undertaking a critical visual task. 


Loss of muscle ability to control the lens power,
"accommodation", also contributes to blurring for near visual tasks
and to the need for spectacles. With advancing age it is no longer possible to
see objects clearly at very short distances from the eye because of our failing
ability to accommodate – a condition called presbyopia. Higher powered lenses
will need to be worn at a VDU terminal, and a bifocal prescription may be
needed for those who also have a visual problem in the distance. Careful
selection of the transition point between the far and near point of a spectacle
lens will be needed for the older VDU user to make long spells at the terminal
acceptable. Operators should mention this when new spectacles are being
prescribed. Good-size text with clear legibility and contrast against the
background is essential for the older worker, who may be encouraged to
experiment with these variables on a computer monitor.


The recent trend has been for large firms to employ visual
specialists on a consultancy basis to assist in the medical department with screening
for both age-related optical and pathological changes to the eye. Staff should
be encouraged to ensure routine eye check-ups, especially in their advancing


Legislation for display screen operators now incorporates
the requirement for visual checks, and even the provision of spectacles for
display screen work. It makes sense to screen all staff in the occupational
setting, not only at pre-employment stage but at regular intervals. This can be
done simply and cheaply with modern equipment.


While great pains are taken to ensure the health of eyes at
work through legislation and recommended practice, in reality it is an area
frequently neglected.


Dr Janet Voke runs regular practical Eyes at Work
training courses. Tel: 01483 861213; fax 861210

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