چكيده لاتين :
propriate for the visual task performed. Optimal lighting is one of the most
important issues in providing the physical conditions of different places, especially the workplace. Lighting can provide comfortable working conditions, especially visual comfort. Life on Earth cannot be imagined without light. Defects in the qualitative and quantitative aspects of lighting in the workplace can cause visual discomfort and reduce the productivity and efficiency of an individual. Therefore,
monitoring the intensity of brightness and color temperature of light is essential to maintain and enhance the health of employees. The quantity and quality of lighting can also affect one's mental health. For example, one of the factors associated with depression is the defect in the quantity and quality of ambient lighting. Correlated color temperatures (CCT) of light play an important role in human psychological and physiological needs. In regards of human perception, two of the most important characteristics of lights are illumination and correlated color temperature (CCT).
Studies have proven that different CCT provided by different lighting are important in affecting human beings psychologically and physiologically, through their visual and non-visual processes.. According to European standard EN 12665, visual comfort is definedsectional study was carried out on 40 professional computer users, aged between 20 and 30 years old, who used the computer at least 4 hours per day in 2018. The inclusion criteria were as follows: Age range
20 to 30 years, no amblyopia, no strabismus, no history of refractive surgery,
no pathological eye diseases and systemic diseases such as diabetes, high blood
pressure and MS and do not take any ophthalmic and systemic drugs that affect
the eyes such as the antidepressants and antibiotics. A questionnaire was used
to assess visual complications in four sections: eye strain, visual dfficulty, ocular disorders and extra ocular disorders. Then, visual examinations including: visual acuity in far and near distances, heterophoria measurement in far and near distances, stereoacuity, accommodation amplitude, accommodation facility and response, near point of convergence, fusional vergence, contrast sensitivity in the four spatial frequencies of 3, 6, 12 and 18 cycle per degree
and tear break up time were performed. Refractive errors were measured
using a Japanese-made Topcon Autokerato Refractometer (ARK-KR.8800,
Topcon, Tokyo, Japan). The monocular and binocular vision was recorded
with the best optical correction at a distance of 6 meters and 40 centimeters
by logarithmic chart based on the Log MAR system. The deviation of cases
Iran Occupational Health Iran Occupational Health. 2020 (5 Dec);17:50.
Original Article
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Iran Occupational Health. 2020 (5 Dec);17:50 2
was measured by the cover test method at a distance of 6 m and at 40 cm. To
examine the accommodation amplitude, the near point of accommodation was
measured using the push-up method. The accommodation response of cases
was measured by Monocular Estimation Method (MEM). The near point of
convergence was also measured by push-up method. The TNO random dot
test was used to assess stereopsis. Fusional vergences were measured by prism bar both at a distance of 6 m and at 40 cm. To measure contrast sensitivity, the
CSV-1000 Chart (VectorVision, Inc., OH, USA) was used. By measuring the
tear break up time, the stability of the tear film were examined and the cases of dry eye were identified by using the slide lamp and fluorescent. For statistical analysis, descriptive statistics including concentration and dispersion criteria of SPSS 20 were used.
Results: In this study, the mean and standard deviation of age was 26.48±2.72
.Also, the mean and standard deviation of using computer was 5.82±0.84 hours per day (range 4 to 8 hours). According to the results, the mean visual acuity of all cases with the best optical correction was 0.0 logarithm. At a distance of 40 cm, 70% of the cases had no heterophoria and 30% of the cases had exophoria with less than 10 prism diopters. The means and standard deviations of blur, break and recovery by base out prism at 6 meter were: 11.40±3.30, 17.85±4.11 and 12.78±3.83 prism diopter, respectively and at 40 centimeter were
17.59±2.76, 25.40±5.16 and 17.25±3.49 prism diopter, respectively and by base
in prism at 6 meters were: 0.55±1.28, 8.80±1.80 and 6.30±1.78 prism diopter,
respectively and at 40 centimeter were: 12.90±2.67, 19.05±3.02 and 14.05±2.77
prism diopter, respectively. The means and standard deviations of stereoacuity, accommodation amplitude, accommodation facility and response, near point of convergence and tear break up time were respectively; 52.0±11.36 seconds of arc, 9.65±2.48 diopter, 10.5±3.0 cycle per minutes, 0.35±0.23 diopter, 2.85±3.37 centimeters and 7.45±3.17 seconds and the means and standard deviations of contrast sensitivity in the spatial frequencies of 3, 6, 12 and 18 cycle per degree were 1.75±0.11, 2.11±0.14, 1.86±0.13 and 1.44±0.13 log units, respectively.
According to the questionnaire, the most common complaints were in the
ocular surface problems section with 32% and eye strain with 27%.
Conclusion: In this study, two important issues were discussed. The first issue includes questions related to computer vision problems for professional users and the other is the results of eye examinations of them. In the first part, based on the questionnaire, the most complaints were in the section of ocular surface
disorders with 32% and eye strain with 27%. In fact, long-term computer usage
causes symptoms such as; Feeling dryness, burning, tearing when working with
a computer and eye strain.
In the second part, it was found that the contrast sensitivity at all frequencies
and the accommodation amplitude were nearly decreased, and in a low
percentage of people, a decrease in the accommodation facility were observed.
The tear break up time was significantly decreased. Stereopsis of the cases was
in the normal range and according to this study was not affected by computer
work. In this study, at a distance of 6 m, heterophoria in the cases were in the
normal range of exophoria, and at a distance of 40 cm, 30% of cases had small
degrees of exophoria. One of the reasons for the increase in near exophoria
in these people can be a decrease in the accommodation amplitude and also
recede of the near point of convergence, which can cause symptoms such as
fatigue, headache, blurred vision and diplopia. According to Morgan's table of
normal values of fusional vergences, the fusional versions of the studied cases
Mousavi N, et al.
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3 Iran Occupational Health. 2020 (5 Dec);17:50
were in the normal range at 6 meters and 40 centimeters. In the present study, the near point of convergence of more than 5 cm was considered as a problem and statistical studies showed that 75% of users had a near point of convergence of less than 5 cm. So this study showed that the near point of convergence was
not affected by working with a computer.
An examination of the accommodation facility of the cases showed that the
binocular accommodation facility in 35% of people was less than 10 cycles per
minute. Accommodation facility helps to maintain a clear and single image
while working in near distance. If accommodation facility is reduced, the
flexibility to focus at a variety of viewing distances immediately after long-term
use of the computer will be difficult, which can cause blurred vision and eye
strain in some users.
The accommodation response of cases were within the normal range of 0.5±0.25
diopter. If the accommodation response is greater than the accommodation
diopter stimulation, symptoms such as blurred vision and eye fatigue were
reported. This study found that, this eye function was not affected by computer
use. Considering the average age of the cases, the accommodation amplitude of less than 8 diopters was considered as a decrease in the accommodation amplitude, which about 35% of people had 8 diopters or less than 8 diopters, but the mean accommodation amplitude was within normal range. Prolonged use of the computer can reduce the accommodation amplitude and cause symptoms such as fatigue and blurred vision. The exact cause of this decrease is
not clear, but it seems to be more due to accommodation fatigue.
In the present study, the mean contrast sensitivity decreased in all spatial
frequencies. However, according to the normal values provided by Vectorvision
for ages 20 to 55 years, the contrast sensitivity in the spatial frequencies of
3, 6, 12 and 18 cycles per degree were: 1.84±0.14, 2.09±0.16, 1.76±0.17 and
1.33±0.19 in the logarithmic unit, respectively. So, the contrast sensitivity of
users was within the normal range. In this study, tear break up time of more
than 10 seconds was considered to be normal and less than this amount was
considered as a problem in the stability of the tear film. Working with computer
affects the pattern of blinking, eye level hemostasis and tear film function. In
fact, reducing the rate of blinking disturbs the balance of replenishment and
evaporation of the tear film. On the other hand, if the screen angle is higher
than the primary gaze of viewing, this evaporation will occur more frequently,
which will cause symptoms such as burning, redness and tearing in computer
users. To reduce eye problems and symptoms, users can be advised to rest
their eyes at regular intervals. It is also recommended that future studies use
qualitative tests in addition to quantitative tests to assess the tear layer. The
impact of computers and other devices such as mobile phones and tablets on
the visual functions of different age groups can also be examined.
