Purpose
To investigate tear function and prevalence of dry eye disease (DED) in visual display terminal (VDT) users.
Design
Cross-sectional study.
Methods
Six hundred and seventy-two young and middle-aged Japanese office workers who used VDT completed questionnaires and underwent dry eye testing. We estimated the prevalence of DED using logistic regression analysis to examine associations between DED and possible risk factors. The ocular surface feature, prevalence of DED, and risk factors were evaluated.
Results
Of the 672 workers, 561 (83.5%, mean age: 43.3 ± 9.1 years) completed the questionnaire. The percentage of women with a composite outcome of definite DED or probable DED was 76.5%, which was higher than that among men (60.2%; odds ratio [OR] = 2.00; 95% confidence interval [CI], 1.29-3.10, P = .002). Workers over 30 years of age had a higher risk of DED (OR = 2.22; 95% CI, 1.06-4.66), as did workers using a VDT >8 hours per day (OR = 1.94; 95% CI, 1.22-3.09). Average Schirmer value was 18.7 ± 11.7 mm and tear break-up time (TBUT) was 4.0 ± 2.5 seconds (78.6% of study participants had TBUT ≤5 seconds).
Conclusions
DED is prevalent among young to middle-aged Japanese VDT users. Ophthalmic findings revealed short TBUT and corneal staining accompanied by normal Schirmer test values. Increased risk for DED was noted for women aged over 30 years and prolonged VDT use. Measures to modify the adverse impact of VDT use on the ocular surface may provide a positive impact on public health and quality of life for office workers using VDTs.
Dry eye disease (DED) is an important public health problem causing ocular discomfort, fatigue, and visual disturbance that may interfere with daily activities. Dry eye is one of the most prevalent eye diseases and reasons for seeking eye care. Based on data from the largest epidemiologic studies of DED—the Women’s Health Study and the Physicians’ Health Study—it has been estimated that about 7.8% or 3.23 million American women and 4.7% or 1.6 million men over 50 years of age have DED. Other studies have evaluated the prevalence of DED in different parts of the world. It is thought that many people have less severe symptoms and probably a more episodic manifestation of DED that is noticed only during exposure to certain contributory factors such as visual display terminals (VDTs).
Home use of computers and portable information terminals has risen steadily, and VDT exposure is increasingly common not only in VDT workers but also in the general population because of widespread use of mobile devices or smart phones among both young and old.
We previously reported the prevalence of DED in VDT users using a questionnaire-based assessment, and found that clinical diagnosis or severe symptoms were prevalent among young and middle-aged Japanese office workers. Although there have been a number of largely anecdotal reports relating DED symptoms to VDT use, only a few studies have investigated tear function and estimation of the magnitude of the problem or risk factors that might be amenable to modification. The authors therefore set out to investigate tear function and to estimate the prevalence of DED among Japanese office workers who use VDTs, and tried to identify key risk factors based on clinical examinations by dry eye specialists and implementing the latest version of the Japanese dry eye diagnostic criteria. The aims of this study were to study tear function, to estimate the prevalence of and factors associated with DED, and to evaluate its ocular manifestations in Japanese men and women who use VDTs.
Methods
Study Population
Under the supervision of the Japanese Dry Eye Society, the authors arbitrarily selected 2 large companies listed on the Japanese stock market and sent a letter to the industrial physician of the health management section of each company to explain the purpose of the study and to request their participation. The only company in the pharmaceutical sector that responded to our letter and consented to participate was enrolled in this study. Following an internal review of the protocol and the consequences of the study, permission was granted to conduct the study in employees who were willing to participate. Subjects were invited by e-mail to answer the questionnaires and to attend a general ophthalmic check-up. A maximum of 2 e-mail reminders were sent. Subjects who reported a history of refractive surgery were excluded from the study protocol. This cross-sectional research followed the tenets of the Declaration of Helsinki, and the protocol was approved prospectively by the Institutional Review Board of Ryogoku Eye Clinic Tokyo, Japan.
Questionnaire
We administered a dry eye questionnaire widely used in Japan. Briefly, the questionnaire includes 12 questions pertaining to the diagnostic symptoms of DED. Possible answers to questions regarding symptoms included “constantly,” “often,” “sometimes,” and “never.” Subjects who responded to more than 1 of the 12 questions by “constantly” or “often” were considered positive for subjective symptoms of DED. Information on age, sex, and smoking (current smoker or not) was also obtained. Based on our previous studies, we defined the duration of VDT use (stratified, none to over 10 hours in 1-hour categories) and contact lens (CL) use (yes or no). Past/current history of certain common systemic diseases (hypertension [HT], diabetes mellitus [DM]) was determined by asking participants whether they had ever been told of these conditions by their physician. We defined systemic medication use as medication prescribed only by a doctor, and not over-the-counter supplements.
Clinical Evaluation
Tear function tests and ocular surface evaluation
Ophthalmic examinations included assessment of conjunctival and corneal vital staining with lissamine green and fluorescein, tear break-up time (TBUT), and Schirmer test. The condition of the ocular surface was evaluated as reported previously. Briefly, corneal and conjunctival epithelial damage was evaluated by the double vital staining method. Two microliters of a preservative-free combination of 1% lissamine green and 1% sodium fluorescein were instilled into the conjunctival sac by micropipette. To evaluate keratoconjunctival epithelial damage, the cornea and conjunctiva were assessed by fluorescein and lissamine green staining, respectively. The eye was categorized into 3 equal compartments representing nasal conjunctiva, cornea, and temporal conjunctiva, and the maximum staining score for each area was 3 points. Overall epithelial damage was scored on a scale of 0-9 points.
Tear stability and quantity were assessed by 2 different methods: TBUT and Schirmer test. To determine TBUT, fluorescein vital staining was performed; patients were requested to blink 3 times to ensure adequate mixing of the fluorescein dye with tears. The time interval between the last complete blink and the appearance of the first corneal dark spot was measured by stopwatch, with the mean of 3 measurements regarded as TBUT in this study. The Schirmer test was performed without topical anesthesia, following all other examinations. Strips (Whatman No.41; Showa, Tokyo, Japan) were placed for 5 minutes at the outer one third of the temporal lower conjunctival fornix. The strips were then removed, and the length of filter paper that had been wetted (in mm) was recorded. To avoid the influence of conjunctivocorneal staining on the Schirmer test, we proceeded with that test after a 10-minute interval. The grading of meibomian gland dysfunction (MGD) was performed according to modified Bron’s classification, as follows: grade 0, no glandular dropout and easy meibum expressibility with clear transparent meibomian secretion; grade 1, glandular dropout in one third of the eyelid length, with acinar cluster visibility in the remaining eyelid, granular secretion, difficult expressibility, turbid, nonsticky secretion; grade 2, glandular dropout in one third of the eyelid with loss of acinar cluster visibility but with observable yellow stripes, meibomian secretion not easily expressible, opaque, white granular secretion; grade 3, meibomian seborrhea with increased sticky secretion. All ophthalmic examinations were performed by ophthalmologists specializing in DED. To avoid the influence of air conditioning on TBUT and other dry eye tests, we did not use any air conditioner in the examination room. The room temperature was maintained at 25.0°C-26.5°C during examinations, with 60%-65% humidity. Subjects were not allowed to use a VDT for 1 hour prior to their examinations.
Diagnosis of dry eye disease
Diagnosis was established according to the Japanese dry eye diagnostic criteria, as follows: (1) presence of dry eye symptoms; (2) presence of qualitative or quantitative disturbance of the tear film in 1 or both eyes (Schirmer test ≤5mm or TBUT ≤5 seconds); and (3) presence of conjunctivocorneal epithelial damage (total staining score ≥3 points) in 1 or both eyes. The presence of all 3 criteria was necessary for a definite diagnosis of DED. Subjects showing the presence of 2 of the 3 criteria were diagnosed with probable DED, while those with 1 or no positive criteria were diagnosed as non-DED ( Table 1 ). With the aim of comparing differences between dry eye diagnosis in our study group and Japanese and international diagnostic criteria, we also implemented the Dry Eye WorkShop (DEWS) severity grading system to assess differences in diagnosis.
| Symptoms of dry eye a | + | − | + | + | + | − | − | − |
| Tear abnormality b | + | + | − | + | − | + | − | − |
| Epithelial damage c | + | + | + | − | − | − | + | − |
| Dry eye diagnosis | Definite dry eye disease | Probable dry eye disease | Non–dry eye disease | |||||
a At least 1 positive sign of dry eye questions.
b The presence of at least 1 positive criterion is essential: (1) Schirmer test-I ≤5 mm; or (2) TBUT ≤5 seconds.
c The presence of at least 1 positive criterion is essential: (1) total score of fluorescein ≥3 points; or (2) lisamine green staining ≥3 points.
Statistical Analysis
To compare differences in the Schirmer test, TBUT, epithelial staining, and MGD grading between sexes, we used Student t test. The prevalence of DED was calculated and the corresponding 95% confidence interval (CI) estimated. Using a logistic regression model, we calculated odds ratios (ORs) and 95% CIs of DED for sex, demographic, lifestyle, and medical factors. First, we carried out univariate analyses of the associations between each factor and definite and probable DED. Then, mutual adjustment for all associated factors identified in univariate analyses ( P < .2) was performed. Although the age category was not associated with diagnosis of DED in univariate analysis, we collapsed age into 2 categories (≤30 and >30 years) and included this variable in the multivariable models, since previous studies found age to be an important risk factor for DED. We categorized prolonged VDT working hours as >8 hours, since the average was 7.9 hours for all subjects. P values of <.05 were considered to indicate statistically significant differences. All statistical analyses were performed using SAS software, version 9.2 (SAS Inc, Cary, North Carolina, USA).
Results
Of the 672 office workers approached, 561 (83.5%) participated in this study: 374 male (66.7%) and 187 female participants (33.3%) aged between 22 and 65 years ( Table 2 ). Participants ranging in age from 30-49 years accounted for 68.8% of the study population. The mean duration of VDT use was 7.7 ± 2.1 hours among men and 8.3 ± 2.3 hours among women. Most workers were healthy, with only 14.4% reporting any type of systemic disease and 24.2% reporting the use of systemic medication.
| Variables | Men (n = 374) n (%) | Women (n = 187) n (%) |
|---|---|---|
| Age (y) | ||
| 22-29 | 14 (3.7) | 20 (10.7) |
| 30-39 | 87 (23.3) | 68 (36.4) |
| 40-49 | 150 (40.1) | 81 (43.3) |
| 50-65 | 123 (32.9) | 18 (9.6) |
| Current smoker | 105 (28.1) | 5 (2.7) |
| VDT use (hours) | ||
| 0-4 | 55 (14.7) | 18 (9.5) |
| 4-8 | 246 (65.7) | 110 (58.8) |
| >8 | 73 (19.5) | 59 (31.5) |
| Contact lens user | 77 (20.6) | 93 (49.7) |
| Past/current history of certain common systemic diseases | ||
| Hypertension | 24 (6.4) | 3 (1.6) |
| Diabetes mellitus | 6 (1.6) | 0 (0.0) |
The results of ocular findings are shown in Table 3 . The average Schirmer test value was 16.7 ± 11.5 mm in men and 22.6 ± 11.2 mm in women, and 83.1% of all subjects had a Schirmer score >5 mm. Mean TBUT was 4.3 ± 2.7 seconds in men and 3.4 ± 1.9 seconds in women, and 78.6% of subjects showed a TBUT of ≤5 seconds. Most subjects scored low on epithelial staining: 471 of 561 (83.9%) under 3 points and only 1 patient (0.2%) with 7 points or over. Meibomian gland scoring showed that 279 of 374 (74.6%) in men and 154 of 187 (82.3%) in women were grade 0, with no statistically significant difference by sex ( P = .08).
| Men (n = 374) | Women (n = 187) | Total (n = 561) | P Value | |
|---|---|---|---|---|
| Schirmer (mm) | ||||
| >5 | 296 (79.1%) | 170 (90.9%) | 466 (83.1%) | .0001 |
| ≤5 | 78 (20.9%) | 17 (9.1%) | 95 (16.9%) | |
| Mean ± SD | 16.7 ± 11.5 | 22.6 ± 11.2 | 18.7 ± 11.7 | |
| TBUT (seconds) | ||||
| >5 | 96 (25.7%) | 24 (12.8%) | 120 (21.4%) | .0005 |
| ≤5 | 278 (74.3%) | 163 (87.2%) | 441 (78.6%) | |
| Mean ± SD | 4.3 ± 2.7 | 3.4 ± 1.9 | 4.0 ± 2.5 | |
| Epithelial staining (points) | ||||
| 0-2 | 327 (87.5%) | 144 (77.0%) | 471 (84.0%) | .001 |
| 3-6 | 46 (12.3%) | 43 (23.0%) | 89 (15.8%) | |
| 7-9 | 1 (0.2%) | 0 (0.0%) | 1 (0.2%) | |
| Mean ± SD | 1.0 ± 1.3 | 1.4 ± 1.4 | 1.1 ± 1.3 | |
| MGD (grade) | ||||
| 0 | 279 (74.6%) | 154 (82.3%) | 433 (77.2%) | .084 |
| I | 69 (18.4%) | 19 (10.2%) | 88 (15.7%) | |
| II | 16 (4.3%) | 9 (4.8%) | 25 (4.4%) | |
| III | 10 (2.7%) | 5 (2.7%) | 15 (2.7%) |
The prevalence of DED by sex is shown in Table 4 . The proportion of women with a composite outcome of definite DED (18.7%) was higher than that of men (8.0%). Most instances of definite DED were seen among subjects who met the criteria of symptoms, epithelial damage, and TBUT ≤5 seconds. One hundred and ninety-five of 374 men (52.1%) and 108 of 187 women (57.8%) were diagnosed as having probable DED ( P = .24). The majority of subjects with probable DED (70.3% of men and 85.2% of women) had symptoms and TBUT ≤5 seconds. The next most frequent group consisted of subjects with symptoms, TBUT ≤5 seconds, and an abnormal Schirmer value. The non-DED group was composed of 149 men (39.8%) and 44 women (23.5%), and 39.3% of this group had TBUT ≤5 seconds, followed by a group of subjects with symptoms only (26.9%).
| Men (n = 374) | Women (n = 187) | |||
|---|---|---|---|---|
| No. of DED | Prevalence (95% CI) | No. of DED | Prevalence (95% CI) | |
| Definite dry eye disease | 30 | 8.0 (5.5-11.3) | 35 | 18.7 (13.4-25.1) |
| Symptom + epithelial damage + TBUT≤5 + Schirmer ≤5 | 9 | 2.4 (1.1-4.5) | 6 | 3.2 (1.2-6.9) |
| Symptom + epithelial damage + TBUT≤5 | 21 | 5.6 (3.5-8.5) | 29 | 15.5 (10.6-21.5) |
| Probable dry eye disease | 195 | 52.1 (46.9-57.3) | 108 | 57.8 (50.3-64.9) |
| Symptom + Schirmer ≤5 | 15 | 4.0 (2.3-6.5) | 0 | 0 (0-2.0) |
| Symptom + TBUT ≤5 | 137 | 36.6 (31.7-41.7) | 92 | 49.2 (41.8-56.6) |
| Symptom + TBUT ≤5 + Schirmer ≤5 | 27 | 7.2 (4.8-10.3) | 8 | 4.3 (1.9-8.3) |
| Epithelial damage + Schirmer ≤5 | 2 | 0.5 (0.1-1.9) | 0 | 0 (0-2.0) |
| Epithelial damage + TBUT ≤5 | 8 | 2.1 (0.9-4.2) | 7 | 3.7 (1.5-7.6) |
| Epithelial damage + TBUT ≤5 + Schirmer ≤5 | 3 | 0.8 (0.2-2.3) | 1 | 0.5 (0-2.9) |
| Symptom + Epithelial damage | 3 | 0.8 (0.2-2.3) | 0 | 0 (0-2.0) |
| Non–dry eye disease | 149 | 39.8 (34.8-45.0) | 44 | 23.5 (17.6-30.3) |
| Symptom only | 37 | 9.9 (7.1-13.4) | 15 | 8.0 (4.6-12.9) |
| Schirmer ≤5 only | 7 | 1.9 (0.8-3.8) | 0 | 0 (0-2.0) |
| TBUT ≤5 only | 58 | 15.5 (12.0-19.6) | 189 | 6 (5.8-14.8) |
| Schirmer ≤5 and TBUT ≤5 (normal in epithelial damage and symptom) | 15 | 4.0 (2.3-6.5) | 2 | 1.1 (0.1-3.8) |
| Epithelial damage only | 1 | 0.3 (0-1.5) | 0 | 0 (0-2.0) |
| Normal in 3 categories | 31 | 8.3 (5.7-11.6) | 9 | 4.8 (2.2-8.9) |
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