The present study showed that the prevalence of CVS was 75.6% (95% CI=70.0, 81.1). Studies found that the prevalence of CVS worldwide ranges from 25% to 93%. The finding of present study is in line with study conducted in Gondar, Ethiopia among bankers which reported prevalence of CVS to be 73%. The result of this study is also similar with several studies from other countries which found prevalence of CVS to be 74% among computer users in Abuja, Nigeria, 72% among university students in Ajman, United Arab Emirates and 73.9% among operator of call center in São Paulo, Brazil.
However, our prevalence is lower than study conducted among university engineering students in Chennai and Malaysia which reported prevalence of CVS to be 81.9% and 89% respectively. The possible reason for higher prevalence in these studies may be university students use computers and other electronic devices for a longer time and even over night for the purpose of studying than secretary employees whom only spends their day work time on computer. On the other hand, in our study only the symptoms which lasted at least one week were considered as symptoms of CVS whereas they had no specification on duration of symptoms and therefore even transient symptoms might be included.
In contrast, the result of our study is higher than study conducted among office workers in Sri Lanka and information technology professionals in Chennai that found the prevalence of CVS 67.4%, and 69.3% respectively. The higher prevalence observed in our study may be due to involvement of neck, back and shoulder pain as a symptom of CVS which has been also considered as an extra-ocular symptom of CVS in many studies [8,12], whereas their definition of CVS consisted only of ocular/visual symptoms.
CVS is an umbrella term that covers a wide variety of visual/ocular and extra-ocular symptoms. In the present study, blurred vision (40.6%), extra-ocular symptoms (34.6%) and eyestrain (30.4%) were the most commonly reported symptoms whereas a change in color perception (9.7%) was the least complaint. Similarly, study conducted in Gondar among bankers reported blurred vision (42.4%) and headache (23.0%) as the most frequent complaint by participants. Moreover, eyestrain, blurred vision and headache in descending order were the most common reported symptoms among computer users in Benin, Nigeria.
However, study conducted in Pakistan among university students reported irritation of eyes (48%), headache (38%) and burning sensation (33%) as the most frequent complaint whereas among Sri Lankan computer workers headache was complained by 45.7% while changes in color perception was reported by 9.3% study participants. Al Rashidi et al., reported that majority (62.14%) of participants presented with eye strain while the second symptom was burning sensation in eyes complained by 7.57% of the participants.This difference could be attributed to differences in study participants’ occupation and pain threshold, sampling technique and sample size.
CVS is a problem that is caused by several factors. The present study found average time spent on computer per day as a predictor of CVS. Mowatt et al., found result consistent with current study where 75% of people who spend >6 hours a day on the computer have more visual problems than those who do not. Several studies have shown that an increase in the number of hours spent on computer increases the risk of developing CVS significantly[12,24].
In contrast to present study, study conducted in Gondar among bankers found no significant association between working hours per day and CVS. The reason may be due to the study participants in this area being bank workers most often taking frequent breaks to give services for customers resulting lesser average time spent on computer per day than secretaries that use computers for a longer time without eye break. Likewise, study done in Italy also didn’t find any association between duration of the computer use and CVS.
Duration of occupation was another factor significantly associated with CVS in the present study. Study by Ranasinghe et al., among computer office workers in Sri Lanka also reported that duration of occupation was significantly associated with CVS. Gupta et al., also found similar result, in which significant association was observed between the symptoms and years of computer usage. However, study conducted by Arumugam et al., did not found significant association.
The present study also found that adjustment of computer screen brightness was factor significantly associated with CVS. Study conducted in Uttar Pradesh, India among computer operators working in different offices and banks found that eyestrain, headache and watery eyes were significantly reported by more number of subjects who work with computers without adjusting the brightness of the screen. However, in study among computer office workers in Sri Lanka adjusting the brightness of screen was not significantly associated with CVS.
Brightness is one of the key features of a computer screen, which should be adjusted to provide balance with room lighting and maximum visibility. Brightness causes images and words on screen to become blurry especially at its edge. Blurred images are known to cause stimulation of accommodation which leads to ciliary muscle to tire easily and develop symptoms of CVS like blurred vision and eyestrain. Adjustment of the brightness level according to the workplace significantly reduces CVS symptoms like eyestrain and watering[26,27].
Moreover, awareness about CVS and its prevention measures was strongly associated with CVS in the current study. Studies show that most problems associated with computer use are caused by insufficient knowledge about safe computer usage. Sufficient knowledge about CVS and its preventive measures would minimize or prevent the occurrence of CVS[8,11].
This study has certain limitations. First, the obtained data on symptoms of computer vision syndrome were based on subjective report by study participants and this may lead to over or under estimation of the prevalence of computer vision syndrome. Secondly, ophthalmic examination was not done as a result some of the symptoms of CVS like blurred vision and eye strain that might be caused by uncorrected refractive error might potentially overestimate the prevalence.