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Journal Français d'Ophtalmologie
Volume 41, n° 3
pages 231-237 (mars 2018)
Doi : 10.1016/j.jfo.2017.08.021
Received : 7 May 2017 ;  accepted : 10 August 2017
Articles originaux

Impact of environmental adaptation on tear film assessments
L’impact de l’adaptation environnementale oculaire sur l’évaluation du film lacrymal
 

R. Fagehi
 College of Applied Medical Sciences, King Saud university, Riyadh, Saudi Arabia 

Summary
Purpose

The purpose of this study was to investigate the effect of ocular environmental adaptation on clinical tear film assessment.

Method

Thirty subjects (male, mean age 23±2.5) participated in this study. A number of clinical tear film tests were applied, including: fluorescein tear break-up time (FTBUT), Schirmer test and tear prism height test (TPH). The tear physiology of each subject was evaluated twice, once immediately when they arrived from the external environment, and then after 30minutes adaptation in the exam room environment.

Results

The mean values were: Schirmer test A (22.1±2.99), Schirmer test B (24.2±2.63), FTBUT A (8.00±1.94), FTBUT B (9.13±2.04), TPH A (0.179±0.026) and TPH B* (0.187±0.023). Statistical testing using Wilcoxon-signed rank test showed a significant difference between the Schirmer test results measured at the different times (P =0.008). Also, the FTBUT and tear prism height test results showed significant differences between the two evaluation times, (P =0.001, 0.011, respectively) (A: tear assessed when the subject comes from the outside environment, B: tear film assessed after 30min adaptation in the clinical environment).

Conclusion

This study showed a significant difference between the tear film test results evaluated when the subjects were assessed immediately from the outside environment and after an adaptation time in the clinic environment. Practitioners must consider the effect of differences between external and clinical environment adaptation on clinical tear film physiology.

The full text of this article is available in PDF format.
Résumé
Objectif

Étudier l’effet de l’adaptation environnementale oculaire sur l’évaluation clinique du film lacrymal.

Méthode

Trente sujets masculins (23 ans±2,5 ans) ont participé à cette étude. Les tests cliniques du film lacrymal appliqués étaient les suivants : Fluorescent Tear Break-up Time (FTBUT), test de Schirmer et test de Tear Prism Height (TPH). La physiologie de la larme de chaque sujet a été évaluée deux fois : la première était immédiatement après l’arrivée des sujets de l’environnement externe, la seconde était 30minutes après d’adaptation dans l’environnement clinique (pièce).

Résultats

Les valeurs moyennes des tests effectués étaient les suivantes : test Schirmer A, 22,1±2,99, test Schirmer B, 24,2±2,63 ; FTBUT A, 8,00±1,94 ; FTBUT B, 9,13±2,04 ; TPH A, 0,177±0,026 ; et TPH B 0,187±0,023. « A » indique que le film lacrymogène a été évalué immédiatement après l’arrivée du sujet dans l’environnement extérieur. « B » indique que le film lacrymogène a été évalué après une adaptation de 30minutes dans l’environnement de la clinique. Les tests statistiques effectués à l’aide d’un test de classement (test de Wilcoxon) ont montré qu’une différence significative dans les résultats du test de Schirmer a été mesuré dans deux temps différents (p =0,008). En outre, les résultats des tests FTBUT et TPH ont montré des différences significatives entre le temps d’évaluation (p =0,001, 0,011, respectivement).

Conclusion

Cette étude a montré qu’il existe une différence significative dans les résultats du test de film lacrymal évalués lorsque le film lacrymal des sujets a été évalué immédiatement après l’arrivée des sujets de l’environnement extérieur et après un temps d’adaptation dans l’environnement clinique. Cela dit, les praticiens doivent tenir compte de l’effet des différences entre l’adaptation de l’environnement externe et interne par rapport à la physiologie du film lacrymal clinique.

The full text of this article is available in PDF format.

Keywords : Tear film, Environment, Dry eye

Mots clés : Film lacrymal, Environnement, Œil sec


Introduction

The tear film comprises a complete structure made of elements that are highly interdependent. It provides a smooth, lubricated ocular surface. There is a close relationship between the tear film and surrounding environment; this relationship is essential to maintaining tear film quality and quantity [1].

There are several factors can be affected tear film quality and quantity. These are categorized according to DEWS to internal and external factors. The tear film can be evaluated with a number of clinical tests. These tests are divided to tear film quality and quantity tests. Tear film quality or stability tests may include TBUT, this test was first introduced in 1969 by Norn [2] and it remains the most frequently used diagnostic test to evaluate tear film instability [3, 4]. There is another tear film quality tests techniques can be applied using different devices such as; videokeratoscopy [5], interferometry of the lipid layer [6], confocal microscopy [7] and wavefront aberrometry [8]. There are also a number of clinical tests uses for tear film quantity assessment. These tests are such as; Schirmer test, it was the first to crudely describe tear production and is still the most widely used clinical test [9], phenol red thread test [10] and tear osmolarity test [11].

Tear film quality (stability) and quantity can be affected by several factors such as; age [12, 13, 14], gender, race [15], contact lens wear [16, 17, 18], ocular surgery and environmental stimuli.

Tear film can also be influenced by external environmental conditions such as temperature, humidity, air conditioning, pollution (smoke, other atmospheric irritants) and air currents [19, 20].

Several studies have been investigated the relationship between tear film and the environment. In 1987, Wyon and Wyon reported that tear stability in healthy eyes significantly decreased after 30min exposure to high air velocity (1.0m/s), but moderate air velocity (0.5m/s) for the same period of time had no effect on TBUT [21].

Korb et al., demonstrated that in dry eye patients, the tear lipid layer thickness increase when humidity increased [22]. González-Garcìa et al. [23] showed that in dry eye patients, the NIBUT decreased from 5.3 to 4.9 when the relative humidity was decreased from 34% to 19%. In 2012, a study by Abusharha and Pearce investigated the effect of different humidity levels (5% and 40%, constant temperature 21°C) on tear film using controlled environment chamber showed that there was a significant change in tear film evaporation, tear break-up time, lipid layer thickness and tear production adversely affected by low humidity [24]. In 2015, a similar study investigated the effect of different ambient temperatures (5, 10, 15, 20 and 25°C/constant relative humidity 40%) on tear film. They reported that chronic exposure to low temperature would result in significant change in human tear film and symptoms of ocular dryness [25].

These previous studies make us wonder does the tear film assessment obtain when the patient arrive from the external environment, particularly in hot climate (low humidity and high temperature) countries such as Saudi Arabia, is accurate? Or shall the practitioner take in consideration an ocular adaptation period before clinical tear film assessment?

It is reasonable to expect that the different ambient environment will be affected the tear production, tear stability and tear volume. Therefore, a series of tear film test include Schirmer test, fluorescein tear break-up time and tear prism height have been applied in this study to investigate the effect of external and clinical environments on clinical tear film assessments.

Materials and methods

Thirty subjects (male, age 26.4±4.5 years) have been recruited to take part in this single-center study. The inclusion criteria were>21 years old, non-contact lens wearers, no history of ocular or systemic diseases reported. This study followed the tenets of the Declaration of Helsinki [26].

All participants asked to come to the clinic for one visit, a number of tear film tests have been applied, these included Schirmer test-I, fluorescein tear break-up time (FTBUT) and tear prism height test (TPH) using slit-lamp biomicroscopy.

These tear film tests were applied on each participant twice. First, immediately when the subject arrived from the outside environment. Secondly, after 30-minute adaptations in the clinical environment.

This study has been done in optometry department clinic, which is located in KSU university in downtown. All the clinical tests have been done at the same period of time between 8 am and 12:30 pm in May, where the external temperature and humidity as shown in (Table 1). While the internal (clinical environment) were; temperature (mean±SD: 25±3.5°C) humidity (mean±SD: 32±5.2).

The comparison was made between the tear film results assessed at two different times to investigate the effect of external and clinical environment on tear film assessment.

Schirmer test I

The Schirmer test was the first to crudely describe tear production and is still the most widely used clinical test [27]. The test uses a filter paper strip placed over the lower lid. The Schirmer test is a well-established clinical procedure performed to help diagnose chronic dry eye disorders. The test involves inserting a strip of filter paper between the eyeball and the lower eyelid for several minutes to collect natural tears. Based on the amount of moisture absorbed, a doctor can determine the severity of dryness. The procedure usually takes about 5minutes to complete and can be performed in an optometrist clinic.

Fluorescein tear break-up time (FTBUT)

FTBUT can be used to evaluate the stability of tear film, with instability indicated by a break-up time of<10seconds [28]. Sodium fluorescein solution (2%) was installed into the inferior palpebral conjunctiva. The subject then asked to blink completely and gently for three times. The slit-lamp cobalt blue filter was used to observe the stability of tear film. The appearance of first pre-corneal spot or any irregularity interrupting the homogenous fluorescein pattern was recorded as the break-up time in seconds.

Tear prism height test

Measuring the tear meniscus formed on the lower lid margins gives a useful guide to tear volume. This simple technique employs the slit-lamp biomicroscope. With experience, the approximate prism is graded as minimal, normal or excessive. Grading is not accurate in the presence of reflex tearing.

An alternative technique is to compare the tear prism height with the illuminated slit width by setting the slit horizontally in alignment with the lower lid margin, altering the slit width until it appears to match the height of the tear prism. A value in millimetres can be obtained by a one-off calibration of the knob rotation controlling the slit width, using a microscope scale. The normal distribution of tear prism heights, peaking at 0.22mm. It is important to ensure the patient is in a primary position of gaze, as the apparent height of the meniscus can depend on this.

Results

The test of normality using (Kolmogorov–Smirnov) showed that the data was normally distributed (P >0.052).

The differences between the tear film results assessed at the two occasion showed that after 30min adaptation in clinical environment it was slightly better or at least equal to the results when its assessed at time (A), for each subject, (Table 2).

The mean values of Schirmer test (A) (22.1±2.99) and Schirmer test (B) (24.2±2.63). FTBUT (A) (8.00±1.94) and FTBUT (B) (9.13±2.04). TPH (A) (0.179±0.026) and TBH (B) (0.187±0.023), Table 2. The statistical tests using (Wilcoxon-signed rank test) showed that a significant different exist between the Schirmer test results measured on the two different occasions (P =0.008) (Figure 1). Also, for the fluorescein TBUT (Figure 2) and tear prism height (Figure 3) the results showed significant differences between the two evaluation times, (P =0.001, 0.011, respectively).



Figure 1


Figure 1. 

Box plots showing the difference between schirmer test results measured directly from outside environmental (schirmer test A) and after 30min adaptation in clinic (Schirmer test B).

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Figure 2


Figure 2. 

Box plots showing the difference between FTUBT test results measured directly from outside environmental [FTUBT (A)] and after 30min adaptation in clinic [FTUBT (B)].

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Figure 3


Figure 3. 

Box plots showing the difference between TPH test results measured directly from outside environmental [TPH (A)] and after 30min adaptation in clinic [TPH (B)].

Zoom

Discussion

This study compared the tear film physiology at two different occasions. First, immediately when the subject has arrived clinic from the external environment. Then, after 30minutes adaptation in the clinical environment.

The environmental conditions have an effect on tear film [20, 29, 30, 31, 32, 33]. In the very cold countries or that is very hot and/or dry environment countries, this effect is more expected.

The results of this study showed that after 30minutes adaptation in a clinic environment, the tear film assessment results were slightly better. For Schirmer test and FTBUT, the percentage of subjects who showed improvement in tear film test result is (70% and 76%, respectively). For the TPH, the percent is less (26%).

The statistical tests showed that significant differences exist when the tear film evaluated on the two different occasions for the all three tear film tests applied; Schirmer test (P =0.008), FTBUT (P =0.001) and TPH (P =0.011).

The observed differences in tear film quantity and/or quality affected by the environment is agreed with some of the previous studies that have investigated the effect of environment on human tear film.

The human tear film characteristic is considerably affected by the ambient temperature. A desiccating environment can lead to increase tear film evaporation and reduce in tear turnover rate. These lead to exposure of the ocular surface to hazardous environmental elements, therefore, exacerbate dry eye symptoms.

The environmental factors that may cause dry eye are categorized to indoors factors: closed ambient like office settings, which have variations in airflow, humidity, time in front of the computer and other video displays. Outdoor factors: exposure to open areas with extreme temperatures, gases, and air suspended particles in the desiccating wind, UV exposure, petrochemical industries, urban traffic, and polluted environments.

Outdoor air pollution, such as exposure to traffic pollution has been associated with adverse effects on the pre-corneal tear film (PTF) in the forms of discomfort and reduced BUT [29, 34, 35].

PTF alteration has been also associated with traffic proxies such as nitrogen dioxide [36, 37, 38], particulate matter [39, 40] and smoke from fires [41].

Air velocity, the stagnant layer around ocular surface can disappear by high air velocity along the head region [42] and may, therefore, enhance the tear evaporation rate [43]. An exposure to a high air velocity>1.4m/s for 30minutes may slightly decrease BUT and tear meniscus height particularly in DED patients [44].

Ocular surface temperature is shown to correlate with dry eye symptoms [45]. A high initial ocular surface temperature may be associated with a thicker lipid layer in normal subjects but not a stable pre-corneal tear film [46].

Relative humidity, the recent epidemiological studies have shown a strong association between low RH and the prevalence of dry eye symptoms [20, 47]. In 2012, Abusharha and Pearce have been assessed the human tear film at two different humidity environment (desiccating humidity 5% and normal humidity 40%) with constant ambient temperature (21°C). They reported that tear film production is adverse significantly affected by the desiccating environment [24].

In 2015, Abusharha et al. [25] investigated the effect of ambient temperature on the human tear film using controlled environment chamber. A constant relative humidity of 40% and different temperatures (5, 10, 15, 20 and 25°C) were applied. They reported that a threefold increase in tear evaporation rate was observed as the ambient temperature increased. The mean tear break-up time decreased from 12.35s at 25°C to 7.31 at 5°C.

Conclusion

The tear film clinical evaluation can be affected by the ocular environmental adaptation particularly when there is a difference between the external and internal environment. This study showed that a significant different is exist when the tear film was evaluated immediately after the subject arrived from the external environment and after an adaptation in a clinical environment. The practitioners must be considered this environmental effect especially in very cold or very hot countries and where the air-conditioner is commonly used.

Disclosure of interest

The author declares that he has no competing interest.


Acknowledgements

The authors extend their appreciation to the college of Applied Medical Sciences Research Centre and Deanship of Scientific Research at King Saud University for its funding for this research.

Also, I would like to express my thanks to Rakan Alshoail OD, for his help in data collection.

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