Subjects
This was a prospective randomized controlled study. The study was conducted at the Eye Center of the Second Affiliated Hospital of Zhejiang University School of Medicine between September 2020 and December 2020. The study protocol adhered to the tenets of the Declaration of Helsinki and was approved by the Ethics Committee of the Second Affiliated Hospital of Zhejiang University School of Medicine. This study was registered with the Chinese Clinical Trial Register (https://www.chictr.org.cn/, No. ChiCTR2000029342).
Volunteers over the age of 18 with basic reading ability participated in this study, and who had ocular diseases, had a history of eye surgery within 6 months, wore contact lenses within 1 month, or used topical eye drops within 1 month were excluded. Also, pregnant or lactating women and volunteers with severe systemic diseases were excluded. Written informed consent was obtained from all participants after the nature and possible consequences of the study had been explained to them.
Study treatment
Participantswere randomly allocated to three groups and each individual accepted 2 hours smartphone reading task. After reading for 1h, each group took different rest methods. Group A: no rest, group B: eye-closed rest for 10mins, group C: added one drop of artificial tears (URSAPHARM Arzneimittel GmbH, Germany) then eye-closed rest for 10mins. Questionnaires and ophthalmological examinations were performed before and after the 2 hours reading task. The study flowchart is represented in Figure 1.
Hisense A6 was applied in the study (relevant parameters are shown in Table 1.Within the experimental period, the subjects were placed in rooms with the same light, temperature, and humidity. The brightness of the screen was set at 80% of the maximum brightness of the smartphone. To make the comparison of results easier, all text fonts and sizes were unified. The distance between the screen and the subjects’ eyes was approximately 40cm. The reading time of the three groups was from 8:00 to 10:00 in the morning for 2 hours. The latter two groups rested in different ways for 10 minutes after reading for 1 hour. During the reading period, the subjects cannot do the non-reading behavior for a long time (more than 5 minutes), and the reading posture can be adjusted moderately. In the study, the DED and asthenopia tests were done in the following order: subjective questionnaire, critical flicker fusion frequency (CFF), Non-invasive break-up time (NIBUT), fluorescein tear break-up time (FBUT), corneal fluorescein staining (CFS), and the Schirmer I test (SIT).
OSDI
The subjective severity of DED was determined by the Ocular Surface Disease Index (OSDI) questionnaire. In the OSDI questionnaire, a total of 12 questions were divided into three subscales: (1) ocular symptoms (OSDI symptoms), (2) vision-related function (OSDI visual function), and (3) environmental triggers (OSDI trigger). The 12 items of the OSDI questionnaire were graded on a scale of 0 to 4, where 0 indicates none of the time; 1, some of the time; 2, half of the time; 3, most of the time; and 4, all of the time. The total OSDI score was then calculated based on the following formula: OSDI = [(sum of scores for all questions answered) *100]/ [(total number of questions answered) *4].[16]
Critical flicker frequency(CFF)
The flash fusion frequency was measured by the Digital Flicker(Takei Scientific Instruments Co. Ltd. Tokyo, Japan). The subject sat in front of the instrument and looked at the red flash fusion point in the darkroom with a daily reading posture. The flicker frequency gradually decreased from 60Hz until the subject can distinguish the flicker of light spots with the naked eye. Press STOP immediately to record the resolution frequency. CFF was measured twice and averaged.
Noninvasive break-up time (NIBUT)
Using noninvasive Keratograph 5M (Oculus, Wetzlar, Germany) to measure noninvasive break-up time (NIBUT). The subject sat in front of the instrument and was asked to gaze at the red marker in the instrument. After the examiner accurately calibrated the pupil of the subject, asked the subject to blink twice. The instrument automatically detected the tear film rupture area and rupture time on the subject's ocular surface. The first tear film rupture time and average tear film rupture time were measured and recorded in the left and right eyes respectively.
Fluorescein tear film break-up time (FBUT) and corneal fluorescein stainning (CFS)
FBUT and CFS were measured using fluorescein paper strips (Jinming New Technological Development Co. Ltd., Tianjin, China). A test paper was wetted with saline, and one drop was placed in the lower conjunctival fornix. Under the cobalt blue light of a slit lamp, the subject needs to look straight ahead after opening his eyes. And FBUT was the interval from opening the eyes to the first dark spot on the ocular surface. The average value of each eye was measured 3 times continuously. CFS score was quantified based on the National Eye Institute's system. The system divided the cornea into 5 areas and scored each area separately. 0 point: there was no stain at all; 1 point: isolated fluorescein staining; 2 points: fluorescein spot dyeing fused into a piece; 3 points: corneal epithelial defect. Each area’s score was added up to give a total score ranging from 0 to 15.
Schirmer I Test (SIT)
The upper end of the 5mm * 30mm tear secretion test strip (Jinming New Technological
Development Co. Ltd., Tianjin, China) was folded and gently placed in the middle and outer 1/3 of the lower eyelid conjunctival sac of the subject. The subject needed to close his eyes and sat still for 5 minutes. Then, the length of soaked was recorded.
Sample Size
The research intended to recruit patients in order to have a significant clinical difference with a confidence interval of 95 % power (=0.05) based on a previous research sample size calculation(n=30)[14].
Statistics
Statistical analyses were conducted by SPSS 23.0 (SPSS, Chicago, IL, USA), and GraphPad Prism 8.0 (GraphPad Software, San Diego, CA, USA). Among the indicators before and after reading, CFF and NIBUT all conform to the normal distribution, and an analysis of variance was adopted. OSDI, FBUT, CFS, and Schirmer I test did not conform to the normal distribution, using nonparametric tests. Wilcoxon signed-rank test was used for comparative analysis of intra-group differences between subjective and objective indicators. Kruskal-Wallis H and Mann-Whitney U tests were used for comparative analysis of inter-group differences. All tests were two-tailed, and P ≤ 0.05 was considered a statistical difference.
Table 1 Smartphone parameters.
Smartphone Model
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Screen Size
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Display Resolution
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HisenseA6
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6.8 x 13.6 cm(
6.01 inches)
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2160*1080 pixels
|