Prevalence of symptomatic dry eye disease with associated risk factors among medical students at Chiang Mai University due to increased screen time and stress during COVID-19 pandemic.

Dry eye disease (DED) is one of the most common ophthalmological disorders, resulting from several systemic and ocular etiologies including meibomian gland dysfunction (MGD). During the COVID-19 pandemic, medical students are among the high-risk group for DED, mainly due to the increasing use of a visual display terminal (VDT) for online lectures and psychological stress from encountering several changes. Our study aimed to explore the prevalence of DED using the symptom-based definition and potential risk factors in medical students. This is a prospective cross-sectional study that included medical students at Chiang Mai University between November 2020 and January 2021. All participants were assessed using the Ocular Surface Disease Index (OSDI) questionnaire, the Thai version of the 10-Item Perceived Stress Scale-10 (T-PSS-10), the LipiView® II interferometer, and an interview for other possible risk factors. Overall, 528 participants were included in the study; half of the participants were female. The prevalence of DED was 70.8%. In the univariate analysis, female sex, contact lens wear, and T-PSS-10 stress scores were significantly higher in the DED group (P = 0.002, 0.002, and <0.001, respectively). Moreover, participants with severe DED were likely to have higher meibomian gland tortuosity but not statistically significant. In the multivariate analysis, contact lens use and T-PSS-10 score were significant risk factors associated with the severity of DED. In conclusions, the prevalence of DED in medical students was as high as 70.8%. Contact lens use and psychological stress evaluated using the T-PSS-10 questionnaire had a significant correlation with a risk of DED. Female gender and duration of VDT use were also associated. Most of the risk factors were modifiable and may be used as initial management in patients with DED.

Introduction

In 2017, the Dry Eye Workshop II (DEWS II) organized by the Tear Film & Ocular Surface Society (TFOS) defined dry eye as a multifactorial disease of the ocular surface characterized by a loss of the tear film homeostasis, accompanied by ocular symptoms. Additionally, the tear film instability and hyperosmolarity, ocular surface inflammation and damage, and neurosensory abnormalities play critical roles [1]. The dry eye symptoms (DES) may include ocular dryness, discomfort, pain, grittiness, blurry vision, redness, foreign-body sensation, and visual disturbance, which could significantly disturb daily life activities such as reading, driving, and using visual display terminals (VDT) [2-4].

The reported prevalence of dry eye has been varied among studies due to the inconsistent definition and diagnostic criteria. The meta-analysis yields prevalence of dry eye ranging from 5% to 50% with symptom-based diagnosis and as high as 75% with any positive ocular signs [5]. The prevalence of dry eye disease (DED) in Asians is higher than in Caucasians [5, 6]. In the adult Thai population, the prevalence of DED is reported to be 34% by questionnaire [6].

The identification of DED subtypes, either aqueous deficient or evaporative, is essential for classification and management. However, these subtypes are more considered as a spectrum of disease rather than distinct pathophysiological entities. Evaporative DED is more common, in which meibomian gland dysfunction (MGD) is the most common etiology. The international workshop defined MGD as a chronic, diffuse abnormality of the meibomian glands, usually characterized by an obstruction of terminal duct and/or changes in the secretion of the glands qualitatively/quantitatively. The condition may lead to a tear film alteration, symptoms of eye irritation and inflammation, and ocular surface disease [7]. In a previous study, 65–86% of dry eye patients had MGD [8-10].

Several studies have reported the prevalence and risk factors of DED in university students [11-13]. However, there is limited data regarding the characteristics of DED in medical students [14-17]. Moreover, during the COVID-19 pandemic, medical students are at high-risk for developing dry eye symptoms due to increasing use of VDT for online lectures and psychological stress from encountering several changes. Our study aimed to explore the prevalence and potential risk factors of DED among medical students at Chiang Mai University, Thailand.

Materials and methods

This prospective cross-sectional descriptive study included 528 medical students attending Chiang Mai University, Thailand, between November 2020 and January 2021 with informed consent. The study was conducted in accordance with the tenets of the declaration of Helsinki, and the protocol was approved by the Faculty Ethics Committee. Only medical students who completed the questionnaire and the LipiView® II interferometer examination were included in the analysis. All participants can refuse to be in the study at all, or to stop participating at any time of the study.

A semi-structured questionnaire was designed to assess the dry eye symptoms and their potential risk factors among the medical students during the COVID-19 pandemic. The survey questionnaire had four sections: demographic data with pre-existing medical conditions; risk factors for DED including personal habits; psychological stress; and a dry eye questionnaire using the Ocular Surface Disease Index (OSDI). After completing all questionnaires in Google forms, all participants were examined with the LipiView® ocular surface interferometer.

Participants who had a history of ocular surgery or trauma within 3 months, or ocular diseases such as ocular infection, allergy, autoimmune disease, and those using punctal plug or topical ocular medications other than artificial tears were excluded. Participants who used artificial tears were instructed to stop the use 6 hours before LipiView® II examination.

Ocular Surface Disease Index (OSDI)

The OSDI (Allergan, Inc, Irvine, California) questionnaire is comprised of 12 questions assessing three domains of the ocular surface diseases in dry eyes as follows: 5 questions regarding the dry eye symptoms related to chronic dry eye disease; 4 regarding the limited visual performance related to dry eyes; and 3 regarding the severity of the symptoms in specific conditions during the previous week. Overall scores (range from 0 to100) were calculated and categorized into 3 groups: normal (score 0–12); mild symptoms (score 13–22); moderate symptoms (score 23–32); and severe symptoms (score 33–100) [18].

Psychological stress

The Thai version of the 10-Item Perceived Stress Scale-10 (T-PSS-10) was used to evaluate the psychological stress related to dry eye symptoms. Of 10 questions, 4 positive questions and 6 negative questions were used to quantify the individual’s perceived psychological stress. The scores range from 0 to 40, with higher scores associated with increased perceived psychological stress [19].

LipiView® II ocular surface interferometer

The LipiView® II ocular surface interferometer (TearScience Inc., Morrisville, NC, USA) was used to measure lipid layer thickness (LLT), meibomian gland dropout, meibomian gland dilatation (tortuosity) and blinking pattern. During the test, participants were instructed to maintain fixation on the internal target. All participants were allowed to blink naturally during the image captured, which is typically evaluated for 20 seconds [20].

A single experienced observer (CT) subjectively evaluated the meibomian gland dropout in both upper and lower eyelids using a validated Meibograde grading scheme, with a 4-point scale from 0 to 3 in which grade 0 is 0–25% meibomian gland loss; grade 1, 26–50% loss; grade 2, 51–75% loss; and grade 3, more than 75% loss [21]. The meibomian gland loss was calculated with reference to the equivalent meibomian gland area in healthy individuals. Meibomian gland tortuosity for each eyelid was graded using the 5-point Halleran scale: grade 0, no tortuosity; grade 1, less than 25% tortuosity; grade 2, 26–50% tortuosity; grade 3, 51–74% tortuosity; and grade 4, more than 75% tortuosity [22]. Each eyelid was blinded for evaluation and the upper and lower lids were separately evaluated. The cut-off value for LLT is 60 nm, where the LLT ≤60 nm indicates a chance of MGD with 90% specificity [23]. For the blinking pattern, the incomplete blinking ratio was calculated by the number of incomplete blinks divided by the total blinks [20].

Prevalence of meibomian gland dysfunction (MGD)

Using the validated sensitivity and specificity of the Meibograde as a diagnostic parameter for MGD, as described by Adil et al., a cut-off value of average Meibograde of 0.5 yielded a sensitivity and specificity of 96.7% and 85%, respectively, while a cut-off value of average Meibograde of 0.75 yielded a sensitivity and specificity of 87.9% and 100%, respectively [21].

Statistical analysis

SPSS software for Windows version 25.0 (Armonk, NY: IBM Corp.) was used for the statistical analyses. Data were tested of normal distribution using the Kolmogorov-Smirnov test with the cut-point P-value of 0.05. The prevalence was presented with a mean and 95% confidence interval (CI). For the univariate analysis, the Kruskal-Wallis test and Chi-square test were used for categorical variables, the Mann-Whitney U test and ANOVA test for quantitative variables. For the multivariate analysis, the binary logistic regression was performed. A P-value <0.05 was considered as statistically significant.

Results

Prevalence of dry eye symptoms (DES)

A total of 528 medical students completed all questionnaires and the meibomian gland evaluation using the LipiView® II interferometer. Of those, 252 (47.4%) were male, and 276 (52.3%) were female. The mean (range) age was 20.48 (17–31) years. For the refractive errors, 78.6% (415/528) of the medical students had myopia and 8.71% (46/528) had hyperopia. The use of spectacles (392/528, 74.24%) was more common than contact lenses (69/528, 13.07%). The prevalence of DED based on symptoms (OSDI ˃12) was 70.8%.

Risk factors associated with dry eye symptoms (DES)

Univariate analysis showed that female sex (P = 0.002), contact lens wear (P = 0.002), prolonged hours of contact lens wear (P = 0.004), higher frequency of artificial tears used per day (P = 0.001) and higher score of T-PSS-10 (P <0.001) were associated with increased risk of dry eye symptoms (DES). However, the history of refractive surgery, duration of VDT use, and hours of reading paperwork were not significantly different between those with and without DES. The results from LipiView® II, including incomplete blink to total blink ratio, Meibograde and meibomian gland tortuosity scores, were higher in the dry eye group but not statistically significant. ()

The prevalence of mild, moderate, and severe dry eyes in medical students based on the OSDI score were 24.2%, 18.8% and 27.8%, respectively. shows the results of the univariate analysis of potential risk factors for DES according to the severity of dry eyes. Female sex (P = 0.005), contact lens wear (P = 0.005), prolonged hours of contact lens wear (P <0.001), higher frequency use of artificial tears per day (P = 0.003), longer duration of VDT use per day (P = 0.033) and higher score of T-PSS-10 (P <0.001) were also associated with increased severity of dry eyes. According to LipiView® II, only the meibomian gland tortuosity increased with higher severity of dry eyes, but was not statistically significant. Results of Meibography using Meibograde grading scheme were shown in and Meibomian gland tortuosity in

The Meibograde grading system: subjective grading of meibomian gland loss.

Row A: Dynamic illumination mode (Reflect infrared) of upper lids; Row B: Dynamic illumination mode (Reflect infrared) of lower lids; Row C: Adaptive transillumination mode (Trans infrared) of lower lids.

The Meibomian gland tortuosity grading system.

Row A: Dynamic illumination mode (Reflect infrared) of upper lids; Row B: Dynamic illumination mode (Reflect infrared) of lower lids; Row C: Adaptive transillumination mode (Trans infrared) of lower lids; Row D: Dual mode (combine dynamic illumination and adaptive transillumination) of lower lids.

The results of regression analysis are summarized in . Higher T-PSS-10 score (OR, 1.113; 95% CI, 1.074–1.154; P <0.001) and contact lens wear (OR, 0.287; 95% CI, 0.134–0.615; P = 0.001) were significant risk factors associated with the severity of DES.

Using an average Meibograde of 0.75 as a cut-off value, the prevalence of total MGD in medical students was 60.98% (322 in 528) with 100% specificity of MGD diagnosis [21]. Of these, the prevalence of asymptomatic MGD (OSDI score 0–12 with Meibograde cut off ≥ 0.75) was 17.61% (93 in 528) and symptomatic MGD (OSDI score ˃ 12 with Meibograde cut off ≥ 0.75) was 43.37% (229 in 528).

Discussion

Dry eye disease is the most common presenting ocular surface disease in ophthalmic practice. Though the nature of DED is complex, the key pathophysiology is basically the disruption of tear film homeostasis [1]. However, the signs and symptoms of DED are sometimes poorly correlated. Consequently, no single gold-standard is accepted as a diagnostic marker for DED. For the clinical diagnosis of DED, TOFS DEWS II recommend the use of DED questionnaires to determine the subjective severity of the symptoms and their sequelae on quality-of-life. Additionally, the presence of at least one clinical sign of abnormal tear film homeostasis is required for the diagnosis. Positive ocular signs include decreased tear break-up time, tear film hyperosmolarity, and ocular surface staining [24]. However, in our study, the diagnosis of DED was made solely on the presence of DES, as defined by an OSDI score ˃12. This symptom-based definition has also been widely accepted in clinical practice and research, especially in the large population-based studies [4, 15, 25–27].

Previous studies revealed that the DED, using the Schirmer test for diagnosis, was commonly found in medical students [14, 16]. The study of Yang I et al. in 2019 in Brazilian medical students, which the DED was diagnosed with OSDI score, keratography, ocular surface staining and the Schirmer test, the prevalence of severe dry eyes (OSDI score ˃33) was 12.6% compared with 27.8% in our study. They also found that the duration of VDT use and contact lens wear increased the risk of DED [17]. Hyon et al. demonstrated that stress, female sex, contact lens wear, and duration of using VDT were significant risk factors for DED. The prevalence of DED based on the symptoms in Korean medical students was 27.1% This study evaluated DED in medical students before the COVID-19 pandemics and revealed that DED may have association with psychological stress (using the Perceived Stress Scale 4 (PSS-4) questionnaire) [15]. Additionally, the PSS scores in our study tended to be higher than the study by Hyon et al., though the direct comparison was not allowed due to the different versions used. Therefore, a higher prevalence of symptomatic DED in medical students (70.8%) in our study may be explained by more stressful situation during the COVID-19 pandemic among medical students. The study of engineering students in Tamilnadu, South India also showed a high prevalence of symptom-based DED, 64.1% [28]. This study was similarly conducted during the ongoing COVID-19 pandemic. Higher prevalence of DED was presumably due to increased screen time use and stress.

Our study revealed that female sex was likely to be associated with an increased risk of DED, similar to the previous studies [4, 6, 25, 27, 29–33]. Hyon et al. revealed an association between female gender and the development of DED in medical students (P = 0.026) [15]. In addition, females reported higher rates of dry eye symptom scores impacting their quality of life, more negative side effects from the treatments, and longer time for improvement than males [30, 33]. The higher prevalence of DED in females may be partially explained by the balance of sex hormones, particularly androgen that affects the synthesis and interaction of tear film components [6, 25, 31]. Moreover, there are anatomic differences of the meibomian glands lacrimal apparatus. However, the definite pathophysiology underlying the increased risk of DED in females remains unclear.

Contact lens wear was also one of the associated risks of DED. Possible mechanisms include increased tear evaporation, ocular surface changes, reduced density of the goblet cells, altered mucin production, and meibomian gland dropouts, eventually leading to the disturbance of the tear film homeostasis [34]. Many studies show that contact lens wear along with VDT use significantly increased the risk of DED due to disrupting the tear film stability [4, 27, 35].

This study showed that a longer duration of VDT use was possibly associated with an increased risk of DED, consistent with prior studies [4, 32]. In 2018, Iqbal et al. reported that as high as 68% of the students who used the devices for ˃13 hours per day developed the DED and 28% of students with only ˃3 hours of screen time had symptoms of dryness [36]. Prolonged VDT use may interfere with the tear film instability due to decreased blinking rates and increased tear evaporation [4, 37, 38]. COVID-19 pandemic may impact the development of DES among medical students due to increased digital screen time for online lectures and stress from the spreading of COVID-19. Health promotion with the “20-20-20” rule, which recommends that every 20 minutes, an individual should take a 20-second break and focus their eyes on something at least 20 feet away. and limited screen time may be very helpful.

T-PSS-10 score had a significant association with DED in both the univariate and multivariate analysis. Our study demonstrated the association between psychological stress and DED. Hyon et al. used the stress VAS and PSS-4 and found a similar association in medical students and paramedical workers [15, 26]. Moreover, previous studies show an association between DED and several psychiatric conditions, including depression and post-traumatic stress disorder [39, 40]. For this possible association of psychological stress and DED, medical students are generally living under pressure from high expectations and are at high-risk for developing DED. Further studies, with larger populations, are necessary to evaluate the pathophysiology underlying the association between the DED and stress.

Meibomian gland features and tear meniscus assessment can be used to classify the predominant DED subtypes and severity to guide the proper management. Meibography is an objective test for accurately diagnosing MGD and its severity [41]. The gland area dropout is a quantification grading system widely used to diagnose MGD, either alone or in combination with other tests. When using the cut-off value of 0.5 for average Meibograde, the sensitivity and specificity were 96.7% and 85%, respectively. With a higher average Meibograde of 0.75 as a cut-off value, the sensitivity and specificity shifted to 87.9% and 100%, respectively [21]. Previous studies reported that 65–86% of dry eye patients have MGD [8–10, 41]. Therefore, since the prevalence of DED was 70.8% in our study, the prevalence of MGD should be approximately 46–60.8%. Consistently, the actual prevalence of MGD using Meibograde criteria was 60.98%. Notably, most MGD patients were symptomatic.

There were limitations to this study. Firstly, the data was collected from medical students in a single university, which may not represent all medical students in Thailand. Secondly, no clinical evaluations for the dry eye signs were performed. Though several studies applied the symptom-based diagnosis of DED, the clinical examination is still mandatory for the diagnosis of DED in some cases [24]. Moreover, the prevalence of DED may be varied from the different diagnostic methods. Thirdly, the data was collected during the COVID-19 pandemic, in which medical students had an increase in both digital screen time for online lectures and stress. The prevalence of DED in a normal situation may be different. Further study should be performed in a non-pandemic situation and include medical students from various universities for comparison.

Conclusions

This study revealed a high prevalence of symptomatic DED in medical students (70.8%). Contact lens wear and psychological stress evaluated using the T-PSS-10 questionnaire had a significant correlation with the risk of DED. Female gender, prolonged hours of contact lens wear, higher frequency use of artificial tears per day, and prolonged duration of VDT use was also associated with increased severity and risk of DED. Meibomian gland tortuosity was increased with higher severity of dry eyes but not statistically significant. Using an average Meibograde of 0.75 as a cut-off value, the prevalence of MGD in medical students was 60.98% and was mostly symptomatic.

Questionnaire for Demographic data and risk factors for DED_EN version.

(PDF)

Click here for additional data file.

Questionnaire for Demographic data and risk factors for DED_TH version.

(PDF)

Click here for additional data file.

Perceived Stress Scale-10 (PSS-10).

(PDF)

Click here for additional data file.

Thai Perceived Stress Scale-10 (T-PSS-10).

(PDF)

Click here for additional data file.

OSDI_EN version.

(PDF)

Click here for additional data file.

OSDI_TH version.

(PDF)

Click here for additional data file.

25 Jun 2021

PONE-D-21-18381

Prevalence of symptomatic Dry eye disease with associated risk factors among medical students at Chiang Mai University during COVID-19 pandemic

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Reviewer #1: Chulaluck et al. describe a prospective cross-sectional study aimed to explore the prevalence of symptomatic Dry eye disease (DED) with associated risk factors among medical students at Chiang Mai University during covid-19 pandemic

Comments:

1. Abstract: The study did not include any clinical evaluation of the participants; therefore some of them could potentially have other ocular conditions that may have caused dry eye symptoms.

2. The use of a surgical face mask – which is known to increase dry eye symptoms especially during the COVID-19 pandemic, was not part of the risk factors taken in consideration.

3. The information collected during the study only represented the participants' condition at the day of their examination.

4. Methods section: was not elaborate enough. Exclusion and inclusion criteria are not detailed enough.

5. The LipiView test is designed to measure the thickness of the lipid layer, but recent studies showed that It doesn’t seem to correlate too well with people’s slit lamp exams or symptoms.

6. The study only included medical students from Chiang Mai University, which may not represent all medical students in Thailand.

Reviewer #2: We would like to thank the authors for their work on the Prevalence of symptomatic Dry eye disease with associated risk factors among medical students at Chiang Mai University during COVID-19 pandemic. We think it is a well written paper.

We still would like to give some advice on correction:

1.) Please correct the punctuations. There are lots of mistakes regarding the commas options

Introduction:

2.) Please change “The prevalence of dry eye disease (DED) in Asians is higher than Caucasians.” To “The prevalence of dry eye disease (DED) in Asians is higher than in Caucasians. “ and name a reference

3.) “The international workshop defined MGD as a chronic, diffuse abnormality of the meibomian glands, usually characterized by an obstruction of terminal duct and/or changes in the secretion of the glands qualitatively/quantitatively. Please name a reference

4.) The survey questionnaire had four sections: demographic data with pre-existing medical conditions; risk factors for DED including personal habits; psychological stress; and a dry eye questionnaire using the Ocular Surface Disease Index (OSDI), please attach the questionnaire

5.) Please change “Participants who used artificial tears were instructed to stop using for 6 hours before LipiView® II examination. “ to “Participants who used artificial tears were instructed to stop the use 6 hours before LipiView® II examination.”

LipiView® II Ocular Surface interferometer:

6.) “For the blinking pattern, the incomplete blinking ratio was calculated by the number of incomplete blinks divided by the total blinks.” Please refer to the attached picture

Results:

7.) 392/528 is 74,24% not 85%

8.) 69/528 is 13% not 15%

Table 1:

9.)

10.) Please change “average” to “average”

Discussion:

11.) “Hyon et al.“ Please also name the reference here

12.) “Health promotion with the “20-20-20” rule and limited screen time may be very helpful.“ Please explain this rule

Reviewer #3: Dear author,

Thank you for you submission.

There are some points to consider:

1. The title of the article says that the DED was diagnosed during the COVID-19 pandemic, and the discussion mention that during the pandemic medical students were prone to more stress (by T-PSS-10) and VDT time. There weren’t any comparisons of these variables before and during the pandemic. Moreover, do you have any evidence that the DED symptoms / signs were more severe during the pandemic in comparison to the time before?

2. The article concludes that the medical students in Chiang may had a higher rate of DED comparing other studies. You chose the COVID-19 pandemic as one possible reason. Besides the previous note, some other genetic or environmental factors should be considered.

3. The prevalence of DED was based on OSDI score of >12 and the prevalence was 70.8% which is higher than other articles. However, the articles that were cited used other methods or in combination with OSDI score for diagnosing DED. Therefore it should be mentioned as a limitation.

4. In the discussion you mention female sex was a risk factor for DED, but in the regression analysis (table 3) it was not significant.

5. Another limitation that should be mentioned is that only one observer assessed the Meibomian glands. Did the observer assessed every eyelid separately? Or did he/she assessed all 4 eyelids as one unit knowing that they belong to the same patient? The second option could lead to an observer bias.

**********

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18 Jul 2021

Dear Editor in Chief and all reviewers

Journal of PLoS ONE

Revision of submitted manuscript: [PONE-D-21-18381] - [EMID:7fa3bce5a1aded7e]

Prevalence of symptomatic dry eye disease with associated risk factors among medical students at Chiang Mai University during COVID-19 pandemic

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- All images in Figures 1 and 2 were obtained from participants in this study with informed consent. Moreover, during revision, we have added more photographic techniques (Reflected IR, Trans IR) with references. (21 and 22)

21. Adil MY, Xiao J, Olafsson J, Chen X, Lagali NS, Ræder S, et al. Meibomian Gland Morphology Is a Sensitive Early Indicator of Meibomian Gland Dysfunction. Am J Ophthalmol. 2019;200:16-25. Epub 2018/12/24. doi: 10.1016/j.ajo.2018.12.006. PubMed PMID: 30578784.

22. Halleran C, Kwan J, Hom M, Harthan J, editors. Agreement in reading centre grading of meibomian gland tortuosity and atrophy. Poster presented at American Academy of Optometry annual meeting: November; 2016.

And, the additional figure legends for Figure 1 and 2 as follows:

Fig 1. The Meibograde grading system: subjective grading of meibomian gland loss. Row A: Dynamic illumination mode (Reflected infrared) of upper lids; Row B: Dynamic illumination mode (Reflected infrared) of lower lids; Row C: Adaptive transillumination mode (Trans infrared) of lower lids.

Fig 2. The Meibomian gland tortuosity grading system. Row A: Dynamic illumination mode (Reflected infrared) of upper lids; Row B: Dynamic illumination mode (Reflected infrared) of lower lids; Row C: Adaptive transillumination mode (Trans infrared) of lower lids; Row D: Dual mode (combined dynamic illumination and adaptive transillumination) of lower lids.

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Reviewer #1: Chulaluck et al. describe a prospective cross-sectional study aimed to explore the prevalence of symptomatic Dry eye disease (DED) with associated risk factors among medical students at Chiang Mai University during covid-19 pandemic

Comments:

1. Abstract: The study did not include any clinical evaluation of the participants; therefore some of them could potentially have other ocular conditions that may have caused dry eye symptoms.

- The study focused on the dry eye symptoms evaluating by the questionnaires and the meibomian gland function evaluating by the LipiView® Interferometer.

2. The use of a surgical face mask – which is known to increase dry eye symptoms especially during the COVID-19 pandemic, was not part of the risk factors taken in consideration.

- Thank you for your comment. All students are always wearing a face mask during social activities. Therefore, this factor was equally distributed between groups and has not been included in the analysis.

3. The information collected during the study only represented the participants' condition at the day of their examination.

- Thought the data was collected on one day. However, the questionnaires represented general symptoms during a recent period; moreover, the meibomian gland function does not alter rapidly without any medical interventions. So, our data could effectively describe the prevalence of symptomatic dry eye disease with associated risk factors among medical students at Chiang Mai University during COVID-19 pandemic.

4. Methods section: was not elaborate enough. Exclusion and inclusion criteria are not detailed enough.

- More details of exclusion and inclusion criteria were added in the materials and methods section as follows:

“Only medical students who completed the questionnaire and the LipiView® II interferometer examination were included in the analysis. All participants can refuse to be in the study at all, or to stop participating at any time of the study.”

And

“Participants who had a history of ocular surgery or trauma within 3 months, or ocular diseases such as ocular infection, allergy, autoimmune disease, and those using punctal plug or topical ocular medications other than artificial tears were excluded.”

5. The LipiView test is designed to measure the thickness of the lipid layer, but recent studies showed that It doesn’t seem to correlate too well with people’s slit lamp exams or symptoms.

- In our study, lipid thickness was considered as one factor derived from meibomian gland evaluation. However, in the univariate analysis, the lipid thickness was not significantly different among groups of participants with and without dry eye symptoms.

6. The study only included medical students from Chiang Mai University, which may not represent all medical students in Thailand.

- Thank you for your comment. Though our study included medical students from a single university in Thailand, we believe that our data was useful and could represent the general characteristics of dry eye symptoms of medical students in Thailand for two main reasons. First, our study included a large number of medical students (N = 528). Secondly, we believe that the characteristics of medical students in different parts of Thailand should not be markedly different.

Reviewer #2: We would like to thank the authors for their work on the Prevalence of symptomatic Dry eye disease with associated risk factors among medical students at Chiang Mai University during COVID-19 pandemic. We think it is a well written paper.

We still would like to give some advice on correction:

1.) Please correct the punctuations. There are lots of mistakes regarding the commas options

- The manuscript was revised by a native American speaker. However, we are willing to revise the manuscript again once all corrections are done regarding the English correction.

Introduction:

2.) Please change “The prevalence of dry eye disease (DED) in Asians is higher than Caucasians.” To “The prevalence of dry eye disease (DED) in Asians is higher than in Caucasians. “ and name a reference

- Thank you for your comment. The correction has been done. However, the references for this statement were of number 5 and 6 as follows:

5. Stapleton F, Alves M, Bunya VY, Jalbert I, Lekhanont K, Malet F, et al. TFOS DEWS II Epidemiology Report. The ocular surface. 2017;15(3):334-65. Epub 2017/07/25. doi: 10.1016/j.jtos.2017.05.003. PubMed PMID: 28736337.

6. Lekhanont K, Rojanaporn D, Chuck RS, Vongthongsri A. Prevalence of dry eye in Bangkok, Thailand. Cornea. 2006;25(10):1162-7. Epub 2006/12/19. doi: 10.1097/01.ico.0000244875.92879.1a. PubMed PMID: 17172891.

3.) “The international workshop defined MGD as a chronic, diffuse abnormality of the meibomian glands, usually characterized by an obstruction of terminal duct and/or changes in the secretion of the glands qualitatively/quantitatively. Please name a reference

- Thank you for your comment. The reference for this definition was in number 7 as follow:

7. Nelson JD, Shimazaki J, Benitez-del-Castillo JM, Craig JP, McCulley JP, Den S, et al. The international workshop on meibomian gland dysfunction: report of the definition and classification subcommittee. Invest Ophthalmol Vis Sci. 2011;52(4):1930-7. Epub 2011/04/01. doi: 10.1167/iovs.10-6997b. PubMed PMID: 21450914; PubMed Central PMCID: PMCPMC3072158.

And the reference has already been mentioned in the following paragraph.

“The international workshop defined MGD as a chronic, diffuse abnormality of the meibomian glands, usually characterized by an obstruction of terminal duct and/or changes in the secretion of the glands qualitatively/quantitatively. The condition may lead to a tear film alteration, symptoms of eye irritation and inflammation, and ocular surface disease [7].”

4.) The survey questionnaire had four sections: demographic data with pre-existing medical conditions; risk factors for DED including personal habits; psychological stress; and a dry eye questionnaire using the Ocular Surface Disease Index (OSDI), please attach the questionnaire

- Thank you for your comment. The questionnaire will be added as a supplemental in both Thai and English versions.

5.) Please change “Participants who used artificial tears were instructed to stop using for 6 hours before LipiView® II examination. “ to “Participants who used artificial tears were instructed to stop the use 6 hours before LipiView® II examination.”

- Thank you for your comment. The change has been done as suggested.

LipiView® II Ocular Surface interferometer:

6.) “For the blinking pattern, the incomplete blinking ratio was calculated by the number of incomplete blinks divided by the total blinks.” Please refer to the attached picture

- Blinking pattern is used to assess the quality of blinking. The best quality of blinking pattern is that every blink is complete (defined as the complete apposition of upper and lower lids.). The LipiView could demonstrate the number of incomplete and complete blinks per 20 seconds and also calculate the partial blinking rate (PBR). The reference 20 is added. However, there was no figure for the blinking pattern.

20. Eom Y, Lee JS, Kang SY, Kim HM, Song JS. Correlation between quantitative measurements of tear film lipid layer thickness and meibomian gland loss in patients with obstructive meibomian gland dysfunction and normal controls. Am J Ophthalmol. 2013;155(6):1104-10.e2. Epub 2013/03/08. doi: 10.1016/j.ajo.2013.01.008. PubMed PMID: 23465270.

Results:

7.) 392/528 is 74,24% not 85%

- Thank you for your comment. The change has been done as suggested. (in Results)

8.) 69/528 is 13% not 15%

- Thank you for your comment. The change has been done as suggested. (in Results)

Table 1:

9.)

10.) Please change “average” to “average”

- The change has been done as suggested. (in Table 1)

Discussion:

11.) “Hyon et al.“ Please also name the reference here

- Thank you for your comment. The reference for this definition was in number 15 as follow:

15. Hyon JY, Yang HK, Han SB. Dry Eye Symptoms May Have Association With Psychological Stress in Medical Students. Eye & contact lens. 2019;45(5):310-4. Epub 2018/12/27. doi: 10.1097/icl.0000000000000567. PubMed PMID: 30585856.

And the reference has already been mentioned in the following paragraph.

“Hyon et al. demonstrated that stress, female sex, contact lens wear, and duration of using VDT were significant risk factors for DED. The prevalence of DED based on the symptoms in Korean medical students was 27.1% [15].”

12.) “Health promotion with the “20-20-20” rule and limited screen time may be very helpful.“ Please explain this rule

- Thank you for your comment. The explanation has been added as suggested.

“Health promotion with the “20-20-20” rule, which recommends that every 20 minutes, an individual should take a 20-second break and focus their eyes on something at least 20 feet away. and limited screen time may be very helpful.”

Reviewer #3: Dear author,

Thank you for you submission.

There are some points to consider:

1. The title of the article says that the DED was diagnosed during the COVID-19 pandemic, and the discussion mention that during the pandemic medical students were prone to more stress (by T-PSS-10) and VDT time. There weren’t any comparisons of these variables before and during the pandemic. Moreover, do you have any evidence that the DED symptoms / signs were more severe during the pandemic in comparison to the time before?

- Thank you for your comment. As the study was conducted for the first time during the pandemic, there has been no previous report on the prevalence of dry eye symptoms in this specific population. However, regarding the previous study of the prevalence of dry eye in Thai adults which reported to be 34% [5], the prevalence of dry eye in our study was higher.

2. The article concludes that the medical students in Chiang may had a higher rate of DED comparing other studies. You chose the COVID-19 pandemic as one possible reason. Besides the previous note, some other genetic or environmental factors should be considered.

- Thank you for your comment. Please allow us to clarify the COVID-19 pandemic as a possible reason of higher prevalence of dry eye symptoms. In our study, the COVID-19 pandemic was taken into consideration as the pandemic leads to both behavioral and environmental changes that may aggravate the dry eye symptoms. For example, during the pandemic, most of lectures were conducted via the online programmes which lead to more screen time. Also, the circumstances may stress all the medical students in many ways as discussed in the manuscript. In our study, the genetic factors, though might be significant, but was not included.

3. The prevalence of DED was based on OSDI score of >12 and the prevalence was 70.8% which is higher than other articles. However, the articles that were cited used other methods or in combination with OSDI score for diagnosing DED. Therefore it should be mentioned as a limitation.

- Thank you for your comment. The following statement has been added to the limitation part.

“Moreover, the prevalence of DED may be varied from the different diagnostic methods.”

4. In the discussion you mention female sex was a risk factor for DED, but in the regression analysis (table 3) it was not significant.

- Thank you for your comment. That is correct that in the regression analysis, the p value for female sex was 0.052. Therefore, we stated that female sex was likely to be associated with an increased risk of DED, similar to the previous studies.

5. Another limitation that should be mentioned is that only one observer assessed the Meibomian glands. Did the observer assessed every eyelid separately? Or did he/she assessed all 4 eyelids as one unit knowing that they belong to the same patient? The second option could lead to an observer bias.

- Thank you for your comment. In this study, a single experienced observer (CT) subjectively evaluated the meibomian gland dropouts in both upper and lower eyelids using a validated Meibograde grading scheme. Each eyelid was blinded for evaluation and the upper and lower lids were separately evaluated.

We appreciate for the very helpful review.

Sincerely Yours,

Chulaluck Tangmonkongvoragul, MD

Department of Ophthalmology,

Faculty of Medicine,

Chiang Mai University,

Chiang Mai, Thailand

E-mail: poupae025@gmail.com, chulaluck.t@cmu.ac.th

Submitted filename: Responses to Reviewer_20210711 CT edit.docx

Click here for additional data file.

23 Aug 2021

PONE-D-21-18381R1

Prevalence of symptomatic dry eye disease with associated risk factors among medical students at Chiang Mai University during COVID-19 pandemic

PLOS ONE

Dear Dr. Tangmonkongvoragul,

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Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

Reviewer #3: All comments have been addressed

**********

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Reviewer #2: Yes

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**********

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Reviewer #2: Yes

Reviewer #3: N/A

**********

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**********

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**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Thank you for addressing my comments, you did provided reasonable explanations. The article does provide interesting information regarding the influence of the COVID19 pandemic on medical students in Chiang Mai University.

I would recommend it to be published.

Reviewer #2: We would like to thank the authors for editing their work. We do not have any other points to edit.

Reviewer #3: Dear author,

Thank you for your response.

There are still issues that need to be addressed correctly:

1. Explaining the prevalence of DED by “the pandemic” is not correct, you should evaluate each factor separately. Please add references for comparison of the following factors before and after the pandemic – dry eye prevalence in similar age group (comparing to adults is not sufficient); students’ psychological stress; students’ computer and screen time use.

2. If every eyelid was evaluated separately by the blinded single observer, this should be noted.

**********

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Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

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26 Aug 2021

Dear Editor in Chief and all reviewers

Journal of PLoS ONE

Revision of submitted manuscript: [PONE-D-21-18381R1]

Prevalence of symptomatic dry eye disease with associated risk factors among medical students at Chiang Mai University during COVID-19 pandemic

We do appreciate your valuable time reviewing our manuscript for publication with revision suggestions. So, we would like to submit our thoroughly point-by-point response to your reviews, as stated in the letter of Aug 23, 2021, as follows:

6. Review Comments to the Author

Reviewer #3: Dear author, Thank you for your response. There are still issues that need to be addressed correctly:

1. Explaining the prevalence of DED by “the pandemic” is not correct, you should evaluate each factor separately. Please add references for comparison of the following factors before and after the pandemic – dry eye prevalence in similar age group (comparing to adults is not sufficient); students’ psychological stress; students’ computer and screen time use.

- Thank you for your comment. In our study, the pandemic is not directly a risk factor for DED in medical students, but rather be a unique situation that interfered with the known risk factors for DED. We believe that during the pandemic, medical students had to dramatically change the ways of learning and also their lifestyles which might affect with the DED symptoms. However, due to limited number of the DED prevalence in a specific population like medical students, the comparison group as general adult population might be sufficient, and further studies of the DED prevalence in medical students in Thailand when the pandemic is subsided, is an interesting idea for our future project.

2. If every eyelid was evaluated separately by the blinded single observer, this should be noted.

-Thank you for your comment. The following statement has been added to the methods part.

A single experienced observer (CT) subjectively evaluated the meibomian gland dropout in both upper and lower eyelids using a validated Meibograde grading scheme, with a 4-point scale from 0 to 3 in which grade 0 is 0-25% meibomian gland loss; grade 1, 26-50% loss; grade 2, 51-75% loss; and grade 3, more than 75% loss [21]. The meibomian gland loss was calculated with reference to the equivalent meibomian gland area in healthy individuals. Meibomian gland tortuosity for each eyelid was graded using the 5-point Halleran scale: grade 0, no tortuosity; grade 1, less than 25% tortuosity; grade 2, 26-50% tortuosity; grade 3, 51-74% tortuosity; and grade 4, more than 75% tortuosity [22]. Each eyelid was blinded for evaluation and the upper and lower lids were separately evaluated.

We appreciate for the very helpful review.

Sincerely Yours,

Chulaluck Tangmonkongvoragul, MD

Department of Ophthalmology,

Faculty of Medicine,

Chiang Mai University,

Chiang Mai, Thailand

E-mail: poupae025@gmail.com, chulaluck.t@cmu.ac.th

Submitted filename: Responses to Reviewer_20210826.docx

Click here for additional data file.

15 Nov 2021

10 Dec 2021

Dear Editor in Chief and all reviewers

Journal of PLoS ONE

Revision of submitted manuscript: [PONE-D-21-18381R2]

Prevalence of symptomatic dry eye disease with associated risk factors among medical students at Chiang Mai University during COVID-19 pandemic

We do appreciate your valuable time reviewing our manuscript for publication with revision suggestions. So, we would like to submit our thoroughly point-by-point response (blue fonts) to your reviews (black fonts), as stated in the letter of Nov 16, 2021, as follows:

6. Review Comments to the Author

Reviewer #2: We do thank the authors for addressing our comments. We still have one point to address. We think having an adequate control group is essential. Please look for better comparison to make your data valid. Please look for DED in a more comparable group like other students before the pandemic.

Compare the risk factors for DED one by one before and after the pandemic like "psychological stress", screen and computer time.

- Thank you for your comment. We have added the findings of Hyon et al. study which conducted the study of DED in Asian medical students before the COVID-19 pandemics in the second paragraph of the discussion part as follows:

Hyon et al. demonstrated that stress, female sex, contact lens wear, and duration of using VDT were significant risk factors for DED. The prevalence of DED based on the symptoms in Korean medical students was 27.1%. This study evaluated DED in medical students before the COVID-19 pandemics and revealed that DED may have association with psychological stress (using the Perceived Stress Scale 4 (PSS-4) questionnaire) [15]. Additionally, the PSS scores in our study tended to be higher than the study by Hyon et al., though the direct comparison was not allowed due to the different versions used. Therefore, a higher prevalence of symptomatic DED in medical students (70.8%) in our study may be explained by more stressful situation during the COVID-19 pandemic among medical students.

We appreciate for the very helpful review.

Sincerely Yours,

Chulaluck Tangmonkongvoragul, MD

Department of Ophthalmology,

Faculty of Medicine,

Chiang Mai University,

Chiang Mai, Thailand

E-mail: poupae025@gmail.com, chulaluck.t@cmu.ac.th

Submitted filename: Responses to Reviewer_20211210.docx

Click here for additional data file.

24 Jan 2022

7 Feb 2022

Dear Editor in Chief and all reviewers

Journal of PLOS ONE

Revision of submitted manuscript: [PONE-D-21-18381R3]

Prevalence of symptomatic dry eye disease with associated risk factors among medical students at Chiang Mai University during COVID-19 pandemic

We do appreciate your valuable time reviewing our manuscript for publication with revision suggestions. So, we would like to submit our thoroughly point-by-point response to your reviews, as stated in the letter of Jan 24, 2022, as follows:

6. Review Comments to the Author

Reviewer #3: Thank you for you submission.

Because it may be somehow misleading, I recommend the editor to reconsider the title of the article "during COVID-19 pandemic" as there are no direct causes for dry eye due to COVID-19 as the manuscript suggest, but only indirect risk factors (screen time, face masks).

all other notes has been addressed.

- Thank you for your comment. We have changed the title of the article to avoid misleading as follows:

Prevalence of symptomatic dry eye disease with associated risk factors among medical students at Chiang Mai University due to increased screen time and stress during COVID-19 pandemic

We appreciate for the very helpful review.

Sincerely Yours,

Chulaluck Tangmonkongvoragul, MD

Department of Ophthalmology,

Faculty of Medicine,

Chiang Mai University,

Chiang Mai, Thailand

E-mail: poupae025@gmail.com, chulaluck.t@cmu.ac.th

Submitted filename: Responses to Reviewers_7 Feb 2022.docx

Click here for additional data file.

8 Mar 2022

Prevalence of symptomatic dry eye disease with associated risk factors among medical students at Chiang Mai University due to increased screen time and stress during COVID-19 pandemic

PONE-D-21-18381R4

Dear Dr. Tangmonkongvoragul,

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Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

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Reviewer #2: All comments have been addressed

Reviewer #3: All comments have been addressed

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Reviewer #2: Yes

Reviewer #3: Yes

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Reviewer #2: Yes

Reviewer #3: I Don't Know

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Reviewer #2: Yes

Reviewer #3: Yes

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Reviewer #2: Yes

Reviewer #3: Yes

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Reviewer #3: (No Response)

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Reviewer #3: No

14 Mar 2022

PONE-D-21-18381R4

Prevalence of symptomatic dry eye disease with associated risk factors among medical students at Chiang Mai University due to increased screen time and stress during COVID-19 pandemic

Dear Dr. Tangmonkongvoragul:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

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on behalf of

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Table 1

Univariate analysis of potential risk factors for DES according to the presence and absence of dry eye symptoms.

Parameters	No symptoms of dry eyes (OSDI score 0–12) N = 154	Presence of symptoms of dry eyes (OSDI score >12) N = 374	P-value
OSDI score	5.95±3.37	30.05±13.56	< 0.001†
Age (years)	20.73±1.60	20.38±1.68	0.130†
Sex (M:F) (n)	90:64	162:212	0.002*
Myopia (%)	72.7	81.0	0.035*
Glasses wear (%)	68.2	76.7	0.041*
Contact lens wear (%)	5.8	16.0	0.002*
• Daily contact lens	4.5	6.4
• Monthly contact lens	1.9	10.2
Hours of contact lens wear (hours/day)	0.60±2.30	1.68±4.04	0.004†
Frequency of artificial tears used per day (times/day)	0.12±0.71	0.28±0.84	0.001†
History of refractive surgery (%)	0.6	1.6	0.679*
Duration of VDT use per day (hours)	9.55±3.13	9.88±3.12	0.252†
Hours of paperwork per day (hours)	0.95±1.31	0.88±1.04	0.997†
Stress score (T-PSS-10)	12.84±5.72	16.27±5.69	< 0.001†
Average incomplete blink-Total blink ratio of both eyes	0.62±0.32	0.66±0.29	0.285
Average lipid thickness of both eyes (nm)	61.23±21.20	62.72±19.59	0.302
Meibograde
Average Meibograde of all 4 eyelids (0–3 scale)	0.84±0.59	0.87±0.63	0.665†
Meibomian Gland Tortuosity
Average Meibomian gland tortuosity of all 4 eyelids (0–4 scale)	1.57±0.66	1.67±1.15	0.561†

All data are expressed as mean ± SD, or percentage, as appropriate.

*P-value was calculated using the Kruskal-Wallis test.

†P-value was calculated using the Mann-Whitney U test.

Table 2

Univariate analysis of potential risk factors according to the severity of dry eye symptoms.

Parameters	Normal (OSDI 0–12) n = 154	Mild dry eyes (OSDI 13–22) n = 128	Moderate dry eyes (OSDI 23–32) n = 99	Severe dry eyes (OSDI >33) n = 147	P-value
OSDI score	5.95±3.37	16.55±2.53	26.92±2.99	43.92±9.92	< 0.001†
Age (year)	20.73±1.60	20.33±1.74	20.34±1.62	20.45±1.68	0.890*
Sex (M:F)	90:64	63:65	40:59	59:88	0.005*
Myopia (%)	72.7	74.2	85.9	83.7	0.019*
Glasses wear (%)	68.2	70.3	84.8	76.9	0.016*
Contact lens wear (%)	5.8	13.3	14.1	19.7	0.005*
• Daily contact lens	4.5	2.3	7.1	9.5
• Monthly contact lens	1.9	10.9	7.1	11.1
Hours of contact lens wear (hours/day)	0.60±2.30	1.11±3.20	1.41±3.68	2.35±4.80	0.000†
Frequency of artificial tears used per day (times/day)	0.12±0.71	0.15±0.58	0.20±0.74	0.44±1.05	0.003†
History of refractive surgery (%)	0.6	0.8	3.0	1.4	0.388*
Duration of VDT use per day (hr)	9.55±3.12	9.27±3.00	10.21±3.07	10.19±3.20	0.033†
Hours of paperwork per day (hr)	0.95±1.31	0.92±1.11	0.80±1.12	0.89±0.90	0.738†
Stress score (T-PSS-10)	12.84±5.72	15.73±6.20	15.81±5.28	17.05±5.43	< 0.001†
Average incomplete blink-Total blink ratio of both eyes	0.62±0.32	0.65±0.30	0.69±0.28	0.65±0.28	0.361†
Average lipid thickness of both eyes (nm)	61.23±21.20	64.17±19.71	63.82±19.38	60.72±19.59	0.388†
Meibograde
Average Meibograde of all 4 eyelids (0–3 scale)	0.84±0.59	0.82±0.64	0.91±0.66	0.90±0.60	0.593†
Meibomian Gland Tortuosity
Average Meibomian gland tortuosity of all 4 eyelids (0–4 scale)	1.57±0.66	1.59±0.72	1.65±0.84	1.74±1.55	0.474†

All data are expressed as mean ± SD, or percentage, as appropriate.

*P-value was calculated using the Kruskal-Wallis test.

†P-value was calculated using ANOVA.

Table 3

Regression analysis for factors associated with increasing severity of DES.

Variables	Adjusted for sex, contact lens wear, duration of VDT use and stress score
	Odds ratio (95%CI)	P-value
Female	0.672 (0.449–1.004)	0.052
Contact lens wear	0.287 (0.134–0.615)	0.001
Duration of VDT use per day (hr)	1.027 (0.961–1.097)	0.431
T-PSS-10 (score)	1.113 (1.074–1.154)	< 0.001

Abbreviation: CI = confident interval.