Visual implications of digital device usage in school children: a cross-sectional study

The study included 576 students, 60.6% (349) males; 39.4% (227) females. The mean age of the participants was 13.7 years and the median age was 14 years.

Reading distance influences the magnitude of symptoms experienced by those using digital devices. The optimum focus distance for reading and writing is 30–40 cm from the eyes. Ideal focus distance is greater for computer viewing, as compared to reading and writing. It is suggested that there is lesser eyestrain when the computer monitor is 50–70 cm away from one’s eyes [11]. Smaller digital devices such as mobile phones are usually held at a distance of 20–30 cm from the eyes, fostering conditions for digital eyestrain. Long et al. recently reported that viewing distances are closer and the resulting eyestrain symptoms are greater after reading for 60 min from a smartphone [12]. In the present study, however, more than half of the students (56%) maintained an ideal reading distance.

Improper posture leads to excessive straining of eyes and hunching of the back leading to pain in the neck and back muscles. Previous authors have attributed this to incorrect posture and excessive usage of digital devices [13‐15]. In our study, we didn’t find any relationship between eyestrain and posture. Of note, most students (77%) preferred sitting on a chair, while the remaining students preferred to lie down while reading or using digital devices.

The present study also found that the time spent by students on digital devices each day consistently increases as age increases. It is advised that adolescents should not have screen time for more than two hours a day [15]. This guidance can be challenging for teenagers to follow, particularly since homework frequently requires computer time. Previous studies suggest that the total weekly time spent by adolescents working on computers ranges from 80 to 840 min [15‐21]. The present study showed that approximately half of the 13–16 year old students (46.6%) spent 840–1680 min per week using digital devices. This observation is notable, given that previous studies have documented the association of a wide array of health complaints with excessive use of such devices [15, 17, 22]. Accelerated myopia is just one of a plethora of health complaints associated with excessive screen time [23]. Indeed, a recent study showed that children with diagnosed asthma had 1.6 times higher odds of excessively playing computer games as compared to healthy children (95% CI: 1.11–2.30) and children with learning disabilities had 1.7 times higher odds of risky use of the internet (95% CI: 1.19–2.45) [24]. Excessive screen time may be due to numerous factors including the overuse of technology in school as teaching aids, an increasing burden of homework and unrestrained recreational time (surfing the internet, social networking, playing video games and watching movies).

The use of digital devices is now an essential part of adolescent life style. Adolescents regularly use computers to perform both scholastic as well as leisure activities [25]. In Korea, 60% of the population was reported as using smartphones in August 2012, only a few years after their introduction [26]. In the present study, while analyzing the different types of electronic devices used and the purpose for which they are used, almost 60% students used a smartphone and around two thirds used these devices for school projects. 43.6% of children use smartphones for gaming. Although excessive gaming has been shown to have detrimental health effects [13, 16], a recent review has concluded that the video games do not negatively impact adolescent academic performance in science, mathematics or reading [27].

The crispness of high-definition television screens, laptops and tablets can feel easier on the eyes as compared to older, less defined screens. Most digital screens are backlit and emit blue light or high-energy visible (HEV) light wavelengths. There is evidence that the eye is susceptible to blue light exposure, and that over a period of time the cumulative damage may increase the likelihood and severity of eye disorders (e.g. age-related macular degeneration and cataracts) [28]. Studies are also reporting the negative impact of smartphone usage on sleep. A decrease in melatonin secretion is attributed to the blue light exposure from smartphone displays. Yoshimura et al. have reported that the reduced viewing distance when lying down has a positive correlation to a poorer quality sleep (R2 = 0.27 P < 0.05), longer sleep latency (R2 = 0.35, P < 0.05) and lower sleep efficiency (R2 = 0.38, P < 0.05) [29]. In our study about one fifth of participants, 19.3% (111) used their smartphones at bedtime with lights switched off. We also observed that as age increased, the use of smartphones at bedtime with lights switched off also increased, with the ratio of those using smartphones to those not using them in the age group of 11–12 being approximately 1:10, compared with approximately 1:3 in the 16–17 age group. Studies have previously shown that this type of usage may lead to reduced sleep quality, potentially increasing the likelihood of experiencing other ocular pathologies later in life [10, 28, 29]. However, more studies are needed to establish a causal relationship between digital device usage and ocular diseases.

Due to scarce literature on asthenopia and its correlation with digital device use in children, it is not possible to compare the results of this study directly with other reports. Our results need to be interpreted with caution. Firstly, data was acquired by the student’s self-answered questionnaire, and may therefore be subject to recall bias. Secondly, enrolment in this study was limited to students of urban private schools, and therefore results may not be representative of other populations. A broader study population (for instance including students of government schools or rural schools) may yield varied outcomes. Another limitation of the study was that the age groups were unequally distributed and were not age- or sex-matched. The reading distance in our study could have been measured more objectively using a measuring tape while asking the children to hold a digital device in their habitual position however manpower and time limitation need to be taken into account for taking such measurements in future studies. Despite our best efforts to exclude all causes of decreased vision and convergence insufficiency, existing visual conditions may still have acted as confounders on the prevalence of eyestrain in the population. Thus, recording both presenting and best-corrected visual acuity with the type of refractive error in future studies may help reduce the impact of this confounder. Despite the above limitations, our findings represent an important contribution to the literature, as they suggest that the current wave of digital development may have significant adverse ocular effects. Moreover, the results of this study add to the growing body of evidence investigating the adverse health effects of electronic media use among children.