To evaluate the effect of contact lens (CL) wear and visual display terminal (VDT) work on the ocular surface and tear functions.
Prospective case-control study.
Sixty-nine CL wearers (45 women and 24 men; mean age, 35.2 ± 7.3 years), and 102 age- and sex-matched non-CL wearers were enrolled in the study (66 women and 36 men; mean age, 36.7 ± 7.3 years). Ocular surface and tear function tests, including vital stainings (fluorescein and rose bengal), Schirmer test, tear meniscus height measurement, and tear film break-up time were performed. The subjective symptoms of dry eyes were evaluated using a dry eye symptom questionnaire. The participants were divided into 4 subgroups according to the total time of VDT work in 1 day (VDT work time in 1 day ≥ 4 hours or < 4 hours) and presence of CL wear. Main outcome measures included ocular surface vital staining scores, Schirmer test results, tear film break-up time, tear meniscus height measurement, and symptom questionnaire score.
CL users and long-term VDT workers showed significantly worse tear meniscus height values than non-CL users and short-term VDT workers ( P < .001). The mean visual symptom scores in CL wearers and long-term VDT workers were significantly higher than the other groups ( P < .001).
Office workers who wore CLs and spent more than 4 hours engaged in VDT work had a lower tear meniscus volume with significant dry eye and visual symptoms triggered by environmental factors.
Dry eye is a disease that causes ocular surface damage and various symptoms such as pain and discomfort. Evidence from recent studies suggests that dry eye also can cause visual function impairment. Although contact lens (CL) wear is an established and efficient method to correct refractive errors, dry eye symptoms are common in CL wearers. Several studies report that 50% to 75% of CL wearers had ocular irritation. Even if a lower estimate is used (50%), approximately 17 million Americans have CL-related dry eye. However, in a study reported by Caffery and associates, only 13% of 100 CL wearers were diagnosed with dry eyes by clinical testing.
There are several possible factors that cause dry eye after CL wear. Nichols and Sinnott showed that several factors such as female gender, lenses with higher nominal water content, rapid tear film thinning time, frequent usage of over-the-counter pain medications, limbal injection, and increased tear film osmolarity were related to dry eye status in multivariate modeling. Meibomian gland dysfunction has been linked to dry eye disease. The number of meibomian glands was reported to decrease in CL wear, and the decrease was proportional to the duration of CL wear.
Dry eye-related symptoms have been reported to result in discontinuation of CL wear. According to a previous study by Pritchard and associates, 12% of CL wearers stopped wearing their lenses within 5 years of the initial fitting because of dry eye-related symptoms. Richdale and associates showed that 24.1% of 453 subjects permanently discontinued CL wear and 119 (26.3%) current CL wearers reported CL dissatisfaction. The primary self-reported reason for lens dissatisfaction and discontinuation was ocular symptoms such as dryness and discomfort.
Other than CL wear, visual display terminal (VDT) work also has been reported to be associated with dry eye disease resulting from lower blinking rates and increased tear evaporation with tear film instability. Previously, our group reported in a large-scale epidemiologic study that CL use and VDT work were associated with an increased risk of dry eye disease. In that study, we defined the dry eye disease as presence of a previous clinical diagnosis of dry eye disease by dry eye specialists or the presence of severe symptoms of dry eye disease. Many recent large-scale, population-based dry eye studies have used either self-reported or symptom-based definitions of dry eye that directly reflect dryness to examine factors associated with the disease. However, there is a paucity of data on the effect of CL and VDT work on ocular surface and tear functions. The purpose of the current study was to investigate the effect of CL wear and VDT work on ocular surface and tear functions in office workers.
Sixty-nine CL wearers (45 women and 24 men) aged between 28 and 73 years (mean age ± standard deviation, 35.2 ± 7.2 years) were recruited from the office workers of the Japan Preventive Medicine Society. One hundred two age- and sex-matched volunteer non-CL wearers (66 women and 36 men; mean age ± standard deviation, 36.7 ± 7.2 years) also were recruited from the same office. CL wearers were asked not to wear their CLs the night before examinations. The office environment occupied an entire floor hosting all employees in a large space divided by low partitions, and each individual in this study was exposed to the same humidity and temperature in the same room.
Ocular Surface Vital Staining
The ocular surface was examined by fluorescein and rose bengal staining. Briefly, 2 μL preservative-free 1% rose bengal and 1% fluorescein dyes each were instilled in the conjunctival sac. Rose bengal staining of the ocular surface was scored according to the criteria proposed by van Bijsterveld. The fluorescein staining was scored according to the protocol described by Shimmura and associates. Briefly, the cornea was divided into 3 equal areas of upper, middle, and inferior corneal compartments. Each compartment was graded on a scale of 0 points (no staining) to 3 points (intense staining).
Tear Quantity Evaluation
To evaluate the tear quantity, the Schirmer test without anesthesia was administered. Briefly, the sterilized Schirmer strip (Showa Yakuhin Kako Co Ltd, Tokyo, Japan) was placed in the conjunctival sac for 5 minutes. The length of the wet portion was measured. A value of 5 mm or less was considered abnormal.
Tear Film Stability Evaluation
The standard tear film break-up time (BUT) measurement was performed after instillation of 2 μL 1% fluorescein preservative-free solution in the conjunctival sac with a micropipette. The patients were instructed to blink several times for a few seconds to ensure adequate mixing of the dye. The interval between the last complete blink and appearance of the first corneal black spot in the stained tear film was measured 3 times, and the mean value of the measurements was calculated. A tear film BUT value of 5 seconds or less was considered abnormal.
Tear Meniscus Height Assessment
The tear meniscus was observed with a biomicroscope illumination system (Carl Zeiss Meditec, Inc, Dublin, California, USA) set at a 90-degree angle and tangential to the central inferior meniscus. The beam width was 0.05 mm and the height was 5 mm, with the magnification set at ×32. Tear meniscus height then was assessed by a graticule millimeter scale system (Carl Zeiss Meditec, Inc, Tokyo, Japan) in the ocular eyepiece.
Ocular Surface Symptom Questionnaire
To evaluate the symptoms associated with dry eyes, we implemented a 29-item questionnaire ( Supplemental Material at AJO.com ). The questionnaire consisted mainly of 3 syptom categories: questions related to dry eye symptoms, visual symptoms, and environmental factors. The three parts had 12, 9, and 8 questions, respectively, in each category. Answers to the questions were graded by the frequency of symptoms, which included responses such as always, often, sometimes, rarely, or never. Each frequency was assigned a severity score from 0 to 4 points. The total symptom score was calculated on the basis of the following formula: questionnaire score = [(sum of scores for all questions answered) × 100]/[(total number of questions answered) × 4]. The score of each of the 3 parts of the questionnaire was calculated individually. They were shown similarly as percentage of obtained scores divided by the total possible score in each part.
Questionnaire Regarding Contact Lens Wear and Visual Display Terminal Work
The type of CL and duration of CL wear were obtained from all CL wearers. The duration of VDT work time in 1 day also was obtained from all subjects. To assess the effect of VDT work duration and CL wear on tear functions and ocular surface, subjects were divided into 4 subgroups as: CL wearer/VDT working time/day ≥ 4 hours, CL wearer/VDT working time/day < 4 hours, non-CL wearer/VDT working time/day ≥ 4 hours, non-CL wearer/VDT working time/day < 4 hours.
Dry Eye Diagnosis
The diagnosis of dry eye was based on the diagnostic criteria (2006) of the Dry Eye Research Group in Japan. Briefly, subjects with (1) dry eye symptoms, (2) positive ocular surface staining with fluorescein or rose bengal (3 points or more), and (3) Schirmer test I results of 5 mm or less or tear film BUT values of 5 seconds or less were diagnosed as having definite dry eye. Presence of 2 criteria out of 3 was diagnosed as probable dry eye disease.
The Mann–Whitney U test was performed to test the differences in the ocular surface and tear functions between the 2 groups. The Kruskal-Wallis test was performed to compare the ocular surface and tear function test scores between the 4 subgroups. If statistically significant relations were observed, the Dunn multiple comparison test was performed to detect which pair had a significant difference. Age and sex differences between the groups were studied by the chi-square analysis. A P value of less than .05 was considered statistically significant. Instat software (Graphpad Software, Inc, La Jolla, California, USA) for Macintosh was used for these analyses.
The age and background of each CL group are summarized in Table 1 . Among the subjects, 14 (19.4%) and 51 (76.4%) were rigid gas permeable CL (RGP) and soft CL users, respectively, and 18 (32.7%), 18 (32.7%), and 15 (34.5%) of subjects wore 1-day disposable, 2-week replacement, and 1-month replacement soft CLs, respectively. There were no significant differences in relation to the tear function, vital staining scores, and mean total dry eye severity scores between subjects wearing different types of CLs ( Table 2 ).
|1-Day Disposable CL||2-Week Frequent-Replacement CL||1-Month Replacement CL||RGP CL||Unknown||P Value|
|No. of subjects||18||18||15||14||4|
|Age (years)||36.8 ± 6.9 a||30.0 ± 4.4 a||32.6 ± 7.7||33.6 ± 8.4||31.0 ± 3.7||.005 c|
|Mean VDT time (hrs/day)||8.5 ± 3.5 b||5.6 ± 2.2 b||7.3 ± 1.7||7.5 ± 1.0||6.0 ± 1.2||.03 c|
|Duration of CL use in 1 day (hrs)||12.8 ± 2.3||12.8 ± 1.9||13.2 ± 3.7||12.9 ± 3.6||12.1 ± 1.0||.96|
|Cumulative contact lens wear duration (mos)||170 ± 102.5||154.1 ± 66.7||136.6 ± 52.0||140.4 ± 54.6||140 ± 28.3||.47|
|1-Day Disposable CL||2-Week Frequent-Replacement CL||1-Month Replacement CL||RGP CL||P Value|
|Schirmer I test (mm)||13.7 ± 11.8||16.9 ± 11.3||15.0 ± 10.4||14.3 ± 11.9||.66|
|Tear film BUT (sec)||4.7 ± 2.0||5.1 ± 2.4||3.6 ± 1.7||4.7 ± 1.8||.55|
|Tear meniscus height (mm)||0.53 ± 0.19||0.71 ± 0.33||0.59 ± 0.26||0.57 ± 0.22||.36|
|Fluorescein score (pts)||1.8 ± 1.9||1.8 ± 2.6||2.2 ± 1.6||1.6 ± 1.7||.52|
|Rose Bengal score (pts)||1.5 ± 1.6||1.1 ± 1.4||1.2 ± 0.9||1.6 ± 1.5||.68|
|Mean total dry eye severity score (pts)||35.2 ± 10.5||35.6 ± 13.7||40.2 ± 13.8||30.6 ± 12.6||.55|
Comparison of Tear Functions, Ocular Surface Damage, Symptom Questionnaire Scores, and Probability of Dry Eye Diagnosis between Contact Lens Wearers and Nonwearers
The mean tear meniscus height in CL wearers was significantly lower than that in non-CL wearers ( P = .013). The total dry eye severity score and the 3 subcategory scores from the questionnaire for CL wearers were significantly higher than the scores for non-CL wearers. Moreover, the mean dry eye symptom aggravation score resulting from exposure to air conditioners in CL wearers was significantly higher than that in non-CL wearers ( P = .001). The results are shown in Table 3 .
|Contact Lens Wearer||Non–Contact Lens Wearer||P Value|
|No. of subjects||69||102|
|Age (years)||34.3 ± 7.3||36.7 ± 7.2||.102|
|Schirmer I test (mm)||12.3 ± 9.5||14.7 ± 10.9||.261|
|Tear film BUT (sec)||4.1 ± 1.9||5.0 ± 2.9||.106|
|Fluorescein score (pts)||2.0 ± 1.7||1.6 ± 1.7||.130|
|Rose Bengal score (pts)||1.5 ± 1.3||1.2 ± 1.2||.073|
|Tear meniscus height (mm)||0.58 ± 0.31||0.69 ± 0.34||.013 a|
|Mean dry eye symptom score||39.1 ± 15.0||27.1 ± 15.6||<.001 a|
|Mean visual symptom score||29.2 ± 18.8||20.1 ± 12.9||.002 a|
|Mean environment symptom score||36.7 ± 5.4||15.3 ± 14.7||<.001 a|
|Mean total dry eye severity score||32.3 ± 11.9||25.0 ± 12.7||<.001 a|
|Mean dry eye symptom aggravation score by air conditioners||2.1 ± 1.1||1.3 ± 1.2||<.001 a|
|Distribution of the number and percentages of dry eye diagnosis|
|Normal||15 (21.7%)||36 (35.3%)||.105|
|Probable dry eye||29 (42.0%)||41 (40.2%)|
|Definite dry eye||25 (36.2%)||25 (24.5%)|
The Relationship of Tear Functions, Ocular Surface Damage, Symptom Questionnaire Scores, and Probability of Dry Eye Diagnosis to Duration of Visual Display Terminal Work
The relationship of tear functions, ocular surface damage, symptom questionnaire scores, and probability of dry eye diagnosis to duration of VDT work is summarized in Table 4 . The mean tear meniscus height in the long-term VDT work group was significantly lower than the mean tear meniscus height in the short-duration VDT work group ( P < .001). The total dry eye severity score and the 3 subcategory scores in the questionnaire for the shorter-duration VDT work group were significantly lower than those in the longer-duration VDT work group ( P < .05). The results are shown in Table 4 .
|VDT ≥ 4 Hours/Day||VDT < 4 Hours/Day||P Value|
|No. of subjects||86||85|
|Age (years)||35.0 ± 7.5||36.5 ± 7.1||.193|
|Schirmer I test (mm)||13.6 ± 10.4||13.9 ± 10.5||.974|
|Tear film BUT (sec)||4.4 ± 2.6||4.4 ± 2.6||.234|
|Fluorescein score (pts)||1.7 ± 1.6||1.8 ± 1.8||.464|
|Rose Bengal score (pts)||1.4 ± 1.3||1.2 ± 1.3||.243|
|Tear meniscus height (mm)||0.56 ± 0.30||0.73 ± 0.35||<.001 a|
|Mean dry eye symptom score||37.5 ± 16.0||26.3 ± 14.8||<.001 a|
|Mean visual symptom score||20.3 ± 18.1||19.2 ± 12.4||.01 a|
|Mean environment symptom score||29.1 ± 18.8||18.7 ± 16.3||<.001 a|
|Mean total dry eye severity score||32.7 ± 14.0||23.9 ± 10.2||<.001 a|
|Mean dry eye symptom aggravation score by air conditioners||1.6 ± 1.2||1.5 ± 1.2||.59|
|Distribution of the number and percentages of dry eye diagnosis|
|Normal||24 (27.9%)||27 (31.8%)||.618|
|Probable dry eye||36 (41.9%)||34 (40.0%)|
|Definite dry eye||26 (30.2%)||24 (28.2%)|
The Relationship of Combined Contact Lens Wear Status and Visual Display Terminal Work Duration to Ocular Surface Examination Results, Tear Functions, Symptom Questionnaire Scores, and Probability of Dry Eye Diagnosis
The results from the 4 subgroups are shown in Table 5 . The mean tear meniscus heights in long-term VDT workers wearing CLs and in long-term VDT workers who did not wear CLs were significantly lower than that in the short-term VDT workers who did not wear CLs ( P < .001).
|CL and VDT ≧ 4 Hours||CL and VDT < 4 Hours||No CL and VDT ≧ 4 Hours||No CL and VDT < 4 Hours||P Value|
|No. of subjects||43||26||43||59|
|Age (years)||33.9 ± 7.5||34.9 ± 6.9||36.2 ± 7.4||37.1 ± 7.1||.1019|
|Schirmer I test (mm)||12.2 ± 9.9||12.5 ± 9.0||15.0 ± 10.8||14.5 ± 11.1||.725|
|Tear film BUT (sec)||3.9 ± 1.7||4.4 ± 2.2||5.0 ± 3.1||5.1 ± 2.8||.323|
|Fluorescein score (pts)||1.9 ± 1.5||2.1 ± 1.9||1.5 ± 1.7||1.7 ± 1.7||.446|
|Rose Bengal score (pts)||1.5 ± 1.3||1.5 ± 1.4||1.3 ± 1.4||1.1 ± 1.1||.243|
|Tear meniscus height (mm)||0.56 ± 0.35 a||0.61 ± 0.23||0.57 ± 0.24 b||0.78 ± 0.37 a,b||<.001 c|
|Mean dry eye symptom score||39.6 ± 14.9 a||38.2 ± 15.3 b||35.5 ± 16.9 d||21.0 ± 11.3 a,b,d||<.001 c|
|Mean visual symptom score||34.1 ± 19.0 e,f,g||21.2 ± 15.6 f||22.4 ± 15.1 g||18.4 ± 10.7 e||.0002 c|
|Mean environment symptom score||37.6 ± 14.5 h,i||35.3 ± 17.1 j,k||20.6 ± 18.9 i,k||11.4 ± 9.0 h,j||<.0001 c|
|Mean total dry eye severity score||34.9 ± 12.3 l||30.6 ± 11.0 m||30.5 ± 15.4 n||20.9 ± 8.4 l,m,n||<.0001 c|
|Mean dry eye symptom aggravation score by air conditioners||2.0 ± 1.1 o,p||2.2 ± 1.2 q||1.3 ± 1.2 o||1.3 ± 1.1 o,p,q||.0003 c|
|Distribution of the number and percentages of dry eye diagnosis|
|Normal||8 (7.4%)||7 (26.9%)||16 (37.2%)||20 (33.9%)||.5202|
|Probable dry eye||19 (44.2%)||10 (38.5%)||17 (39.5%)||24 (40.7%)|
|Definite dry eye||16 (37.2%)||9 (34.6%)||10 (23.3%)||15 (25.4%)|