Wednesday June 18 2014
Is office work giving you sore eyes?
“Staring at computer screens all day ‘changes your eyes’, scientists say,” is the headline in The Independent. This follows reports that people who stare at a computer screen experience changes in their tear fluid that are typical of the symptoms of dry eye syndrome (also known as dry eye disease).
Dry eye syndrome is a condition where the eyes do not produce enough tears. This, in turn, can cause eye pain and irritation.
This latest study involved 96 office workers in Japan. They were assessed for signs and symptoms of dry eye syndrome, and questioned on the amount of time they spent in front of a visual display terminal (VDT).
Only very few (9%) met the criteria for dry eye syndrome, but a much greater proportion had signs and symptoms of dry eyes.
There was found to be an association between work time spent using a computer screen and dry eyes.
However, it’s important to note that although the study has demonstrated an association, it cannot prove causation. Therefore, we cannot definitely say that using computers caused these symptoms.
It is also important to note that this was a very small sample, of just 96 people.
If you regularly use a computer, make sure your computer workstation is set up correctly to minimise eye strain. Your screen should stand at eye level, or just below it. It is also advisable to look away from the screen every five minutes for a few seconds and take a few blinks.
Where did the story come from?
The study was carried out by researchers from Keio University in Tokyo, Kyoto Prefectural University of Medicine in Kyoto and Santen Pharmaceutical Co, Ltd in Osaka, as well as Harvard Medical School in Boston, US. Support was provided by Grant-in-Aid for Young Scientists from the Ministry of Health, Labour and Welfare, and the Ministry of Education, Science, Sports and Culture, with additional facilities support from Santen Pharmaceutical Co, Ltd.
The study was published in the peer-reviewed medical journal JAMA Ophthalmology.
The overall reporting of the story by The Independent is accurate, but its headline: “Staring at computer screens all day ‘changes your eyes’” is not strictly correct. While it is true that an association has been found, causation cannot be proven.
It is also important to note that the study was partly funded by Santen Pharmaceutical Co, Ltd which manufactures around 40% of the eye medications available in Japan.
What kind of research was this?
This was a cross-sectional study of a Japanese population of office workers, which aimed to examine the relationship between the concentration of the protein mucin 5AC in tears and the amount of time the person spent in front of a VDT.
In the eye, tears are produced by the lacrimal glands under the eyelid, which produce a salt water fluid, while other glands produce oils. The researchers report that the watery tear fluid contains dissolved mucin proteins, which are produced by cells in the conjunctiva (the thin layer of tissue that covers the inside of the eyelids and white part of the eye).
Mucins are very hydrophilic (“water-liking”) and help to hold water onto the eye’s surface. Previous studies have shown that the concentration of mucin 5AC in the tears is much lower in people with dry eye syndrome.
It has been reported that prolonged use of VDTs is a risk factor for dry eyes and is associated with low levels of mucin 5AC. This study aimed to look at the associations between the number of hours working on a VDT, the severity of dry eye syndrome and the frequency of the symptoms.
The main limitation of such a cross-sectional study is that, despite being able to demonstrate associations, it cannot prove causation.
What did the research involve?
The researchers selected two large companies in the Japanese stock market and recruited 96 individuals who were willing to take part in the clinical examinations, out of a potential 561.
They gave participants a questionnaire on dry eye syndrome (said to be widely used in Japan), which included 12 questions with frequency responses – always, often, sometimes or never.
Responses of “always” or “often” were considered to be positive responses to the particular symptom being questioned.
They additionally answered questions on their age, sex, height, smoking status, contact lens use and VDT use: categorised as short (<5 hours); intermediate; (5-7 hours) and long (>7 hours).
Participants completed clinical examinations to assess the composition of the tears and the function of the eye's surface. The concentration of mucin 5AC in tear samples was assessed in the laboratory.
Dry eye syndrome was diagnosed according to the most recent diagnostic criteria for the condition in Japan. The criteria include:
- presence of symptoms (more than 1 of the 12 questions answered “always” or “often”)
- signs of disturbance of the tear film: a Schirmer test I value of less than 5mm (this test measures the depth of moisture on some special filter paper placed on the lower eyelid) and/or a tear break-up time of 5 seconds or less
- signs of damage to the lining of the surface of the eye and conjunctiva (as indicated by fluorescein or lissamine green staining scores of 3 points or more)
What were the basic results?
The 96 individuals were 63% male, with an average age of 41.7. The average duration of VDT use was 8.2 hours per day.
Most participants had some signs of disturbance of the tear film: 82% of the sample had a tear break-up time of less than 5 seconds and 21% had Schirmer test I values of less than 5mm. However, only a few had signs of damage to the lining of the surface of the eye and conjunctiva.
9 people (9%) met the criteria for definite dry eye syndrome; it was shown to affect a higher proportion of women (5; 13.9%) than men (4; 6.7%). However, over half the total sample (55; 57%) had sufficient signs of probable dry eye syndrome.
The average concentration of mucin 5AC was significantly lower in people with definite dry eye syndrome (3.5ng/mg) than in people without dry eye syndrome (8.2ng/mg).
The average mucin 5AC concentration was also significantly lower in people with VDT usage longer than 7 hours a day (5.9ng/mg) compared to people with VDT usage of less than 5 hours a day (9.6ng/mg).
The average mucin 5AC concentration was also lower in the people reporting symptoms of eye strain, excess tearing or dry eye sensation, compared to people not reporting these symptoms.
How did the researchers interpret the results?
The study suggests that office workers with prolonged VDT had a low concentration of mucin 5AC in their tears, as did those with symptoms of eye strain.
The researchers went on to say that mucin 5AC concentration in the tears may be lower in people with dry eye syndrome than people without.
This small cross-sectional study of 96 office workers in Japan found that while only a few participants (9%) met the criteria for dry eye syndrome, a much greater proportion had signs and symptoms of dry eyes.
The concentration of mucin protein in the tears has previously been associated with dry eye conditions and with prolonged use of VDTs. As the researchers had suspected, people with dry eye disease had a lower concentration of mucin protein in their tears, as did people who worked for longer hours on a computer (greater than seven hours per day), as did those reporting symptoms of eye strain, dry eyes or excess watering of the eyes.
The findings are perhaps not that unexpected. When we work for long hours at a computer screen, we tend to stare fixedly at the same distance for long periods of time and often don’t blink as much as is necessary.
However, it’s important to note that although the study has demonstrated an association, it cannot prove causation. It was not necessarily computer usage that definitely caused these symptoms. For example, we don’t know how long the participants had had these various problems, how long they had been working at a computer screen, whether they had symptoms before or how much they engaged in other activities that may have had an influence (e.g. TV viewing, playing computer games or reading for long periods).
Many of Japan’s citizens spend several hours a day staring at screens, meaning that the association detected in the study may not apply to other nations and cultures.
It is also important to note that this is a very small sample, of just 96 participants. When dividing people into different categories – e.g. according to the presence of different symptoms – those with definite or probable dry eye syndrome, or duration of hours spent on a visual display terminal, the numbers become even smaller. This could reduce the reliability of the associations between mucin concentrations and the factors mentioned above.
A sample of a different or larger group could give different results. Study of other non-office populations or office workers of different age groups would also be useful as a comparison.
Overall, the study shows a very plausible association between prolonged use of a VDT and dry eyes, but it still cannot prove causation.
If you are experiencing symptoms such as dryness, grittiness or soreness that get worse throughout the day, you should see your GP. Dry eye syndrome can lead to complications if left untreated.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.