Vision screening put to the test

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Ways to measure eye health in the workplace are explored by Professor David Thomson as he concludes his short series.

In the second of our two-part series on vision in the workplace, we will consider the principles of vision screening and discuss different ­vision screening equipment.


Vision screeners


Although most of the attributes of vision can be assessed using a few simple charts, the administration of these tests and the interpretation of the subsequent results require some expertise.

Vision screeners are instruments that allow those with minimal knowledge of vision testing to ­ensure that individuals comply with specific vision standards. The instruments contain a simple optical system so that a variety of test stimuli can be presented to each eye at various simulated distances. Instruments with various degrees of automation or computerisation are also available.






quotemarksVision screeners are instruments that allow those with minimal knowledge of vision testing to ­ensure that individuals comply with specific vision standards.”


Most instruments include tests of distance visual acuity, near visual acuity, stereopsis and colour vision. Some also include an assessment of visual acuity at an intermediate distance for users of display screen equipment (DSE) and a variety of binocular vision tests such as phoria and suppression. Top of the range models may include blur tests for long-sightedness, an astigmatism test, contrast sensitivity and a glare test. Some instruments also include a very crude test of peripheral vision.

These instruments are portable and easy to use by those with minimal knowledge of vision assessment. However, the use of non-standard charts and tests is common, and this can produce anomalous results. The artificial test conditions also cast some doubt on the validity of some tests – DSE assessment in particular. Although templates and guidelines for interpreting results are provided by the screeners’ manufacturers, it is difficult to determine the evidence base for recommendations.

In the future, vision-screening kiosks may provide an efficient way of providing self-administered health and wellness screening in the workplace.


Working on computers


The advent of computers has had a major impact on many aspects of our lives. Most people now have some contact with computers at work and computers are being used increasingly for education and leisure.

The introduction of computers has led to dramatic changes in working practices.

Twenty years ago, an office job typically involved a range of ­activities including reading, writing, typing and filing. Switching between activities introduced a short, natural break and the activities themselves were sufficiently varied to require a change in posture and provided variation in mental and visual activity.

Today, many of these activities can be carried out without moving from a computer. This change in working practices has been accompanied by an ­increase in complaints about health problems associated with using computers. Of these, “eye problems” is among the most common.


No long-term health risks


Despite a number of ill-founded reports in the media, there is no reliable evidence that using a computer causes any permanent damage to the eyes or causes a change in refractive error (short- and long-sightedness). However, complaints of “eye strain”, tired eyes, irritation, a burning sensation, redness and blurred vision are surprisingly common among computer users.

So what is it about using a computer that results in the high prevalence of eye-related symptoms? In the early days of computers, screens tended to be rather poor quality and would flicker. However, with the advent of flat-panel LCD screens, the legibility of computer displays has improved dramatically and most experts agree the equipment is no longer a significant factor in eye-related conditions.

In many cases, eye problems are related to poor office ergonomics – in particular, inappropriate positioning of the display screen and poor lighting design. In other ­cases, the symptoms can be explained by inappropriate working practices, such as failure to take adequate breaks. In these cases, eye complaints can often be resolved by simply making changes to the office layout and working practices.

However, using a computer can be a demanding visual task and small eye defects can become ­symptomatic under these conditions. In these cases, symptoms can usually be ameliorated by the provision of appropriate spectacles or contact lenses.

Solving eye-related problems therefore requires a holistic approach, taking account of the working environment, practices and the visual status of the user. Concern about the potential health hazards of computers led the Council of the European Communities (EC) to issue a directive in May 1990 stipulating “minimum safety and health requirements for work with DSE”.

EU member states were required to bring into force the necessary laws and regulations to comply with the directive by 31 December 1992. In the UK, this task fell to the Health and Safety Executive (HSE), and the Health and Safety (Display Screen Equipment) Regulations were duly published in December 1992. There have been several ­revisions of the guidance since and the latest version (2002) can be downloaded from the HSE website. The Regulations apply to any company that uses computer screens and similar equipment.


Controversial regulations


In relation to the eyes, the Regulations state that the employer must ensure that all DSE users are offered an “appropriate eye and eyesight test”. They go on to say that the “employer shall ensure that each user employed by him is provided with special corrective appliances appropriate for the work ­being done by the user concerned where (a) normal corrective appliances cannot be used; and (b) the result of any eye and eyesight test that the user has been given in accordance with this regulation shows such provision to be necessary”.






quotemarksSolving eye-related problems requires a holistic approach, taking account of the working environment, practices and the visual status of the user.”


In other words, employers must offer and pay for an eye examination and provide spectacles if they are required for computer work and the user’s normal spectacles are not appropriate.

These Regulations have been somewhat controversial. Opponents have argued that, given the scant evidence that using a computer presents any greater risk than any other office task, the Regulations represent an unnecessary burden on employers.

Others have argued that they are an important part of promoting health and wellbeing in the workplace and that optimising the vision of computer users makes good sense in terms of their efficiency, as well as their general wellbeing.

Given that probably fewer than 10% of computer users are likely to require spectacles specifically for viewing their display screen, others have argued that vision screening may be a more efficient way to ­implement the Regulations.

The Regulations do make provision for employers to offer vision screening as follows: “Vision screening is a means of identifying individuals with defective vision; however, screening is not designed to find those eye ­defects, such as injury or disease, that may not at first affect vision. Where companies offer this facility, some users may be content with a vision screening test to check their need for a full sight test. However, employers must also provide the full eye and eyesight test to those users who either choose at the outset to exercise their entitlement to the full test, or choose to do so after having had vision screening.”

The Regulations go on to specify: “Where vision screening is offered, the screening instrument or other test method used should be capable of testing vision at the distances appropriate to the user’s display screen work, including the intermediate distance at which screens are viewed (usually between 50cm and 60cm). Where test results indicate that vision is defective at the relevant distances, the user should be informed and referred to an optometrist or doctor for a full sight test.”


Alternative approach


Using vision screening to identify people who may not be seeing their computer screen clearly can reduce the number of staff requesting a full eye examination and its associated costs. However, vision screening is effective only if the test can accurately identify those who are likely to benefit from an eye examination.

Some have argued that the test conditions provided by conventional screening instruments do not provide a good simulation of computer viewing conditions and this limits the validity of the test.

An alternative approach is to use computer-based screening software. The first such system was developed by the author and colleagues in 1994. The software used an intelligent series of on-screen questions to build up a profile of the user, their symptoms, their working environment and working practices. The software then presented a series of vision tests on the computer screen in order to assess vision and visual performance.

Because the tests were presented on the screen, the test conditions were closely matched to their normal working conditions, strengthening the validity of the results.

By analysing the responses to the questionnaire and the vision test results, the software was able to prepare customised recommendations in terms of workstation ergonomics, working practices and the need for a full eye examination.






quotemarksUsing vision screening to identify people who may not be seeing their computer screen clearly can reduce the number of staff requesting a full eye examination and its associated costs.”


The latest version of the software can be run on a kiosk screener for companies with large numbers of computer users or on a PC for smaller companies. The software links to a cloud-based server to provide a complete screening and DSE management solution.


Conclusion


In summary, computers have become ubiquitous in the working environment and complaints of eye problems among computer users are common.

In many cases, factors such as poor workstation ergonomics and inappropriate working practices are responsible. In other cases, an optometric intervention may be required. For larger companies, ­appropriate vision screening can be a cost-effective way of managing DSE issues and complying with the Regulations.

Good vision is essential for many tasks and occupations. The consequences of poor vision in the workplace vary from mild discomfort and sub-optimal efficiency to risk of serious injury or death for the individual or others.

Despite the importance of vision, many people give eye care a low priority in their lives, evidenced by the fact that more than 30% of the population do not have regular eye examinations.

An eye examination by an optometrist not only ensures optimal vision, but also detects the earliest signs of ocular and, in some cases, systemic disease. If everybody had an eye examination every two years there would be little need for ­additional vision screening in the workplace.

However, until this happens, vision screening in the workplace provides a useful safety net to detect those whose vision may be inadequate to safely and ­efficiently perform a specific task.

A degree of caution is required when interpreting the results of ­vision screening tests and making judgments on an individual’s competence to perform a task. Although vision is an important factor, overall competence is determined by a complex interaction between many factors and some form of workplace assessment is often a better indication of an individual’s capability to perform a specific task.

Professor David Thomson is director of eyecare software provider Thomson Software Solutions


References


Alfano PL, Michel GF (1990). “Restricting the field of view: perceptual and performance effects”. Perceptual and Motor Skills; vol.70, issue 1, pp.35-45.

Davison PA (1985). “Inter-relationships between British drivers’ visual abilities, age and road accident histories”. Ophthalmic and Physiological Optics; vol.5, issue 2, pp.195-204.

Gegenfurtner KR, Rieger J (2000). “Sensory and cognitive contributions of color to the recognition of natural scenes”. Current Biology; vol.10, issue 13, pp.805-808.

Good GW, Weaver JL, Augsburger AR (1996). “Determination and application of vision standards in industry”. American Journal of Industrial Medicine; vol.30, issue 5, pp.633-640.

Haegerstr√∂m-Portnoy G (1990). “Color vision”. In: Rosenbloom AA, Morgan MW (eds). Principles and Practice of Pediatric Optometry; pp.449-466. JB Lippincott; Philadelphia.

Haymes SA, Johnston AW, Heyes AD (2002). “Relationship between vision impairment and ability to perform activities of daily living”. Ophthalmic and Physiological Optics; vol.22, issue 2, pp.79-91.

Higgins KE, Wood J, Tait A (1998). “Vision and driving: Selective effect of optical blur on different driving tasks”. Human Factors; vol.40, issue 2, pp.224-232.

Johnson CA, Keltner JL (1983). “Incidence of visual field loss in 20,000 eyes and its relationship to driving performance”. Archives of Ophthalmology; vol.101, issue 3, pp.371-375.

Latham K, Whitaker D (1996). “A comparison of word recognition and reading performance in foveal and peripheral vision”. Vision Research; vol.36, issue 17, pp.2,665-2,674.

North RV (1985). “The relationship between the extent of visual field and driving performance – a review”. Ophthalmic and Physiological Optics; vol.5, issue 2, pp.205-210.

North RV (1993). Work and the Eye. Oxford University Press; New York.

Scott IU, Feuer WJ, Jacko JA (2002). “Impact of visual function on computer task accuracy and reaction time in a cohort of patients with age- related macular degeneration”. American Journal of Ophthalmology; vol.33, issue 3, pp.350-357.

Taylor WO (1975). “Practical problems of defective colour vision”. Practitioner; vol.214, issue 1,283, pp.654-660.

West SK, Rubin GS, Broman AT et al (2002). “How does visual impairment affect performance on tasks of everyday life? The Salisbury eye evaluation project”. Archives of Ophthalmology; vol.120, issue 6, pp.774-780.

Westheimer G (1987). “Visual acuity”. In: Adler’s Physiology of the Eye. Clinical Application (8th ed). CV Mosby Co; St Louis, Missouri, US.

Wolffe M (1995). “Role of peripheral vision in terms of critical perception – its relevance to the visually impaired”. Ophthalmic and Physiological Optics; vol.15, issue 5, pp.471-474.

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