Date Published: April 23, 2019
Publisher: Public Library of Science
Author(s): Masahiko Ayaki, Naoko Tachi, Yoshihiro Hashimoto, Motoko Kawashima, Kazuo Tsubota, Kazuno Negishi, Meng C. Lin.
Tear secretion is critical for maintenance of healthy ocular surface and vision. Most of normal subjects and dry eye patients feel worsening of ocular dryness in the afternoon, however, diurnal variation of tear meniscus volume has not been directly measured because there was no appropriate method. We used a simple, non-invasive technique, tear strip meniscometry (SM) by self-examination. Previous investigations indicated the values of SM correlated strongly with those of the Schirmer test, tests of tear break up time, and tear meniscus height measurement by anterior optical coherence tomography. The purpose of this study was to capture diurnal variation of aqueous availability at the tear meniscus by measuring wetted length using SM through self-examination.
Thirty-six medical personnel (mean age; 35.7 years) participated and SM self-examination was performed using a mirror seven times a day. The strip is applied for 5 seconds to the lateral side of the lower lid tear meniscus without touching the ocular surface.
The measured SM value was the highest upon awakening (4.44 ± 3.14 mm) and gradually decreased in the evening; 3.81 ± 3.12 at 9:00, 3.31 ± 2.72* at 12:00, 2.89 ± 1.88* at 15:00, 2.92 ± 1.87* at 18:00, 2.78 ± 1.85* at 21:00, and 2.89 ± 1.75* at bedtime with statistical significance compared to the value upon awakening (*P < 0.05, Dunnett’s multiple comparison test). Proportion of number of subjects with low SM value (< 4 mm) to total number of subjects was 52.8% upon awakening and 83.3% at 21:00, and gradually increased toward evening. Our results could identify diurnal variation of tear meniscus volume in the general population.
Tear secretion from the lacrimal glands is controlled by the autonomic nervous system, predominantly by parasympathetic input . Tears cover and protect the ocular surface, and stability of the ocular surface is critical for ocular health and vision. Tear secretion deficiency is closely related to dry eye disease (DED) and is diagnosed by a deficit in tear secretion, corneal damage, and related ocular symptoms. It is most prevalent in middle-aged women and often accompanied by decreased quality of life, depression, and sleep disorder [2,3]. Many people feel worse ocular symptoms, including dryness and discomfort, in the evening [4–6]. However, the etiology of this is elusive. The ocular surface can be damaged by blue light [7–9] in the evening, because modern workplaces and homes are equipped with blue light-rich lighting, and self-luminous devices are used throughout the day .
This study was approved by an Ethics Committee of Shinseikai Toyama Hospital (the hospital within which the work was undertaken) (approval number; 150110–1), and it conforms to the provisions of the 1995 Declaration of Helsinki (as revised in Edinburgh, 2000). Written informed consent was obtained from every participant and the study was performed in accordance with approved protocol. The participants were 36 ophthalmic technicians and other health professionals (23 females; mean age, 35.7 ± 10.5 years). Normal vision, systemic health, no ocular comorbidity of all participants was confirmed by ophthalmologists and annual health check-ups conducted at each participant’s workplace. None of the participants used contact lenses, did shift work, or had circadian rhythm disorders according to the validated and sophisticated sleep questionnaire; the Pittsburgh Sleep Quality Index .
All participants successfully performed examinations without complications such as pain or conjunctival injection. The mean, minimum, and maximum SM values (mm) are shown in Table 1 (S1 Fig and S1 Table). Mean SM value at 12:00, 15:00, 18:00, 21:00, and at bedtime were statistically significantly different (P < 0.05) compared to the mean SM value upon awakening. To further clarify the diurnal variation, change from baseline of SM upon awakening is shown in Fig 2. The proportion was calculated by dividing the number of subjects with a low SM value (< 4 mm) with the total number of subjects and it was 52.8% upon awakening and 83.3% at 21:00, and gradually increased toward evening (Fig 3). When compared to the proportion at awakening, proportions measured at all time points were not significantly different: P = 0.475 at 9:00, P = 0.147 at 12:00 and 15:00, P = 0.088 at 18:00, P = 0.054 at 21:00, and P = 0.230 at bedtime (vs upon awakening, chi-squared test), respectively. The maximum value did not exceed 4mm at any time point in nine participants (40.0%). We obtained SM measurements seven times a day using a non-invasive method and our results clearly demonstrated diurnal variation in SM values. Our results, which show that SM value is highest upon awakening and that it decreases in the afternoon and evening, could account for these commonly observed clinical symptoms. High SM values upon awakening might be associated with the turnover and defense mechanisms of tear film during eye closure for sleep . Even for people with high SM value in the morning, tear film status may decline to abnormal levels in the afternoon, and these people might suffer from dryness. We believe that our results reliably indicate changes in tear meniscus volume since medical personnel who are familiar with ophthalmic examinations performed all the measurements. Although further studies are warranted to verify our results with a gold standard method such as the Schirmer’s test with repeated measurements and correlations with symptoms, we believe our study successfully identified diurnal changes in aqueous availability at the tear meniscus in the general population as can be seen in S2 Fig, Source: http://doi.org/10.1371/journal.pone.0215922