Abstract
Background
The widespread use of various video display terminals (VDTs) always had a detrimental impact on ocular health. Prolonged use of smartphones has been one of the leading causes of dry eye (DE) and asthenopia. Therefore, the purpose of this study is to find a simple and effective strategy to combat screen-related DE and asthenopia.
Methods
A group of healthy participants aged 18 and above were randomly assigned to three groups and tasked with a 2 h smartphone reading task. After 1 h of usage, each group adopted different methods of rest: no rest (Group A), a 10 min eye-closed rest (Group B), or a 10 min eye-closed joint artificial tears rest (Group C). Ophthalmological examinations and questionnaires were administered to all participants before and after the 2 h reading task.
Results
90 qualified volunteers, including 29 males and 61 females, were randomly assigned to three groups. Group A demonstrated a significant increase in the severity of DE and asthenopia as evidenced by all the evaluated indices. On the other hand, Group C did not exhibit any notable change in DE and asthenopia symptoms, with an improvement in corneal fluorescein staining (CFS) results ( P > 0.05) when compared to the pre-reading values. Group B showed a significant increase in ocular surface disease index (OSDI) ( P ≤ 0.05) and a decrease in critical flicker frequency (CFF) ( P ≤ 0.05).
Conclusions
Close-eye rest with artificial tears may be a convenient and effective prevention strategy for screen-related DE and asthenopia.
1
Introduction
The widespread adoption of smartphones has connected 4.54 billion people to these devices, making them an integral part of daily life. However, the increasing use and dependence on VDTs, including smartphones, has raised concerns about their impact on human health. , A series of ocular and extraocular symptoms caused by long-time use of VDTs are called video display terminal syndrome (VDTS), the main ocular manifestations are DE and asthenopia.
VDTS was highly prevalent among college students, with young individuals and those who used VDTs for extendedd periods being the most affected. The occurrence of VDTS could pose significant challenges to populations’ visual acuity, impacting their daily work and learning. Current studies indicated that VDT-induced DE was caused by decreased blink rate, blue light affecting corneal epithelial cell viability, and increased ocular surface inflammatory response. However, it is important to note that these effects could vary depending on the specific type of device and its usage mode. Factors such as screen time, viewing position (including distance and angle), cognitive needs, screen resolution and contrast, image refresh rate, screen size, brightness, as well as spectral and other digital characteristics, could all influence the severity of dry eye symptoms. VDT includes different types of devices such as computer monitors, smartphones, tablets, and televisions. Generally, the screen size of smartphones is much smaller than that of other VDTs, with an average size of approximately 5 inches. Due to visual suppression associated with amplitude saccades, the blink rate under smartphone use may be lower than that under other VDTs. Additionally, the lighting level for VDTs use should ideally be half of the normal classroom lighting level, as higher lighting levels may lead to excessive glare and difficulties in visual adaptation. , The brightness of smartphones can be automatically adjusted or manually controlled, whereas in computers, it is typically fixed and users do not frequently change it. If the brightness setting of a smartphone is too high, it may increase the issue of glare, negatively impacting eye comfort and visual health. The distance between the eyes and the screen can also affect the focusing system of the eyes and may result in adaptation issues, including accommodative spasms. Compared to other VDTs, smartphones are used at a closer working distance, which may more easily induce abnormalities in accommodation and convergence capabilities. Therefore, it is expected that DE would be more severe following smartphone use compared to other VDTs.
However, current treatments for DE and asthenopia caused by VDTs had limited efficacy, making preventative measures the best way to cope with the disease. In our previous studies, we focused on the effect of screen performance and found that circularly polarized screens and eINK screens can minimize subjective discomfort and ocular surface disorders when reading on smartphones. , However, considering the issue of penetration rate, we aimed to identify a simple, convenient, and effective prevention strategy. Thus, we designed the following experiments to determine a better reading pattern that could reduce the damage caused by long-time smartphone reading. This study provided new ideas for preventing DE and asthenopia during long-time smartphone reading.
2
Materials and methods
2.1
Subjects
This prospective randomized controlled study was carried out at the Eye Center of the Second Affiliated Hospital of Zhejiang University School of Medicine from September 2020 to December 2020. The study protocol adhered to the principles of the Declaration of Helsinki and was approved by the Ethics Committee of the Second Affiliated Hospital of Zhejiang University School of Medicine (No. 2020-11). It was also registered with the Chinese Clinical Trial Register ( https://www.chictr.org.cn/ , No. ChiCTR2000029342) to ensure transparency and compliance with regulatory requirements.
In the power analysis, we set the significance parameter P to 0.05 and the effect size was ultimately determined to be 0.5. Moreover, aiming for more precise experimental results, we set the power value to 0.9. Under these conditions, the power analysis yielded a minimum sample size of 85. Considering a maximum sample fall off value of 20%, the sample size was finalized to be 90. Participants aged 18 and above with basic reading skills were eligible to participate in this study. Those with eye conditions affecting corneal nerves, a history of ocular surgery within the past 6 months, recent use of contact lenses within the past month, current treatment for DE (excluding artificial tears), such as punctal occlusion or intense pulsed light therapy, as well as pregnant or lactating women, and volunteers with severe systemic diseases were excluded.
2.2
Study treatment
The participants were randomly assigned to one of the three groups and were asked to read on their smartphones for 2 h. After reading for 1 h, each group followed a different rest method: no rest (Group A), 10 min eye-closed rest (Group B), or 10-min rest with 0.1% sodium hyaluronate eye drops (URSAPHARM Arzneimittel GmbH, Germany) (Group C). Ophthalmological examinations and questionnaires were administered to all participants before and after the 2 h reading task. The study flowchart was represented in Fig. 1 .
The study employed Hisense A6 (see Table 1 for relevant parameters) as the device for reading. The subjects were kept in rooms with similar light, temperature, and humidity levels throughout the experimental period. The brightness of the smartphone screen was set at 80% of the maximum brightness, and the text fonts and sizes were standardized for ease of comparison. The distance between the screen and the subjects’ eyes was approximately 40 cm. The reading time for all three groups was from 8:00 to 10:00 in the morning for 2 h. During the reading period, the subjects were instructed not to engage in non-reading activities for extendedd periods (more than 5 min), and they were allowed to adjust their reading posture moderately. After 1 h of reading, the latter two groups rested for 10 min in different ways. The study involved tests for DE and asthenopia in the following order: subjective questionnaire, critical flicker frequency (CFF), non-invasive break-up time (NIBUT), fluorescein tear break-up time (FBUT), corneal fluorescein staining (CFS), and the Schirmer I test (SIT).
| Smartphone Model | Screen Size | Display Resolution |
|---|---|---|
| Hisense A6 | 6.8 × 13.6 cm (6.01 inches) | 2160∗1080 pixels |
2.3
Ocular surface disease index (OSDI)
OSDI questionnaire was used to assess the subjective severity of DE. The questionnaire consisted of 12 questions that were grouped into three subscales: (1) ocular symptoms (OSDI symptoms), (2) vision-related function (OSDI visual function), and (3) environmental triggers (OSDI trigger). Responses were scored on a scale of 0–4, where 0 indicated no symptoms and 4 indicated severe symptoms. The OSDI score was calculated using the following formula: OSDI = [(sum of scores for all questions answered) ∗100]/[(total number of questions answered) ∗4].
2.4
Critical flicker frequency (CFF)
CFF was measured by the Digital Flicker (Takei Scientific Instruments Co. Ltd. Tokyo, Japan). The participant assumed a daily reading posture and looked at the red flash fusion point in a darkroom. The flicker frequency was gradually reduced from 60 Hz until the subject could distinguish the flicker of light spots with the naked eye, at which point the STOP button was pressed to record the resolution frequency. The CFF measurement was performed twice and the average was recordedd.
2.5
Non-invasive break-up time (NIBUT)
NIBUT was measured using the Keratograph 5 M (Oculus, Wetzlar, Germany). Participants were positioned in front of the instrument and instructed to focus on the red marker while the examiner calibrated their pupils. The participants were then asked to blink twice, after which the instrument automatically detected the first rupture time of the tear film on the ocular surface. The experiment was repeated three times, and the average value was recordedd.
2.6
Fluorescein tear film break-up time (FBUT) and corneal fluorescein staining (CFS)
Fluorescein paper strips (Jinming New Technological Development Co. Ltd., Tianjin, China) were used to measure FBUT and CFS. The test paper was moistened with saline and a drop was placed in the lower conjunctival fornix. The subject was asked to look straight ahead after opening their eyes under the cobalt blue light of a slit lamp. FBUT was determined as the time interval between opening the eyes and the appearance of the first dark spot on the ocular surface. The average value of each eye was measured three times in succession. CFS score was evaluated using the National Eye Institute scoring system, which divided the cornea into five areas and graded each area separately. 0: indicates no staining, 1: isolated staining, 2: fused staining, 3: corneal epithelial defect. The scores of all areas were added up to give a total score ranging from 0 to 15.
2.7
Schirmer Ⅰ test (SⅠT)
To conduct the SIT, a tear secretion test strip (5 mm × 30 mm, Jinming New Technological Development Co. Ltd., Tianjin, China) was gently placed in the middle and outer 1/3 of the lower eyelid conjunctival sac of the subject by folding its upper end. The subject was then instructed to close their eyes and remain still for 5 min, after which the length of the strip soaked with tears was recorded.
2.8
Statistics
Statistical analyses were performed by SPSS 23.0 (SPSS, Chicago, IL, USA), and GraphPad Prism 8.0 (GraphPad Software, San Diego, CA, USA). CFF and NIBUT showed normal distributions, and were analyzed using analysis of variance. OSDI, FBUT, CFS, and SIT did not show normal distributions, and were analyzed using nonparametric tests. Intra-group differences between subjective and objective indicators were analyzed using the Wilcoxon signed-rank test. Inter-group differences were analyzed using the Kruskal-Wallis H and Mann-Whitney U tests. All tests were two-tailed, and P ≤ 0.05 was considered a statistical difference.
3
Results
3.1
General information of the subjects
Ninety qualified volunteers, consisting of 29 males and 61 females between the ages of 22–30, were recruited from the community. This age range represented a population with higher rates of VDTs usage. Additionally, it was also a common period for the occurrence of DE. The general information and grouping of the subjects were shown in Table 2 . All examination results were performed on the right eye of the subjects. The pre-reading measurements of three groups, including CFF ( P = 0.915), NIBUT ( P = 0.175), OSDI ( P = 0.966), CFS ( P = 0.07), and SIT ( P = 0.796), indicated no statistically significant differences among the groups. However, the FBUT test showed P = 0.003, indicating a statistical difference, as shown in Tables S1 and S2 . The changes in relevant indicators after reading could be found in Table S3 .
| Group A | Group B | Group C | <SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='p’>𝑝p p | ||
|---|---|---|---|---|---|
| Number | 30 | 30 | 30 | / | / |
| Number of eyes | 30 | 30 | 30 | / | / |
| Sex (male: female) | 0.57 | 0.42 | 0.42 | χ 2 = 0.407 | 0.816 |
| Age | 25.26 ± 2.24 | 24.90 ± 1.60 | 24.90 ± 1.68 | F = 1.220 | 0.300 |
| Years of smartphone use | 9.80 ± 2.36 | 8.80 ± 2.37 | 9.40 ± 3.46 | F = 1.220 | 0.378 |
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