The non-invasive assessment of pre-corneal tear film stability was introduced by Mengher et al. in 1985, but it required a subjective measurement by an examiner [7]. The inter-grader variability observed with subjective examiner assessment had been eliminated by the development of new devices with automated software for NI-BUT quantification [8,9,10]. Significant correlations between NI-BUT and the standard biomicroscopic tear break-up time (TBUT) have been reported [10,11,12]. In addition, it is stated that NI-BUT measurement obtained with a topography device is more advantageous than TBUT measurement because it is objective, more practical, and does not require fluorescein paper and topical anesthesia [12]. Recently, NI-BUT with a cut-off value less than or equal to 10 s had been identified by the Dry Eye Workshop II (DEWS II) as an indicator for DED diagnosis with 82–84% sensitivity and 76–94% specificity [13].

This cross-sectional study aimed to reflect the evaporative effect of using the day-long face mask. A cohort of health care staff was specifically included in the study to better see the effect of uninterrupted mask use. Results revealed that 8 h of continuous face mask use reduced NI-BUT in all subjects having measurable NI-BUT.

It is revealed that the use of face masks may worsen dry eye symptoms. Boccardo revealed that 26% of dry eye symptoms having subjects had increased symptoms with mask wear [14]. Moshifar et al. indicated a marked increase in dry eye symptoms among regular mask users. This was attributed to air blowing from the upper portion of the mask toward the ocular surface, resulting in increased airflow and accelerated evaporation of the tear film, causing irritation or inflammation of the ocular surface when this continues for hours or days [3]. This scenario is similar to worsening dry eye symptoms in patients having CPAP therapy which increases ocular irritation and tear evaporation especially if the mask is improperly fitted [15, 16].

The impact of face masks on dry eye symptoms has been previously discussed in the literature; however, its evaporative aspect has not been adequately discussed quantitatively. Aksoy et al. revealed that 8 h of mask-wearing decreased TBUT and Schirmer test results [17]. However, they evaluated the subjects on different days, and continuous mask wear is based on subjects’ statements. This is the first study, which investigates the impact of 8 h of continuous mask wear on non-invasive dry eye assessment, conducted on the same day. Although this study lacks a non-mask-wearing control group due to the COVID-19 precautions, it is shown before that no significant day-long change in TBUT values occurs in healthy subjects [18, 19].

Based on the OSDI values of subjects, Krolo et al. revealed that a history of prior dry eye disease, female sex, and wearing a face mask longer than 3 h per day could contribute to or worsen dry eye symptoms during face mask-wear [20]. In the current study, OSDI scores of females were slightly higher than males; however, no significant correlation was found between the decrease in NI-BUT value and age, gender, and OSDI score.

Jahanbani-Ardakani et al. stated that OSDI scores of health care staff were greater than the control group (27.2 vs 7.3), and this was attributed to face mask wearing time (10.1 vs 1.2 h) [21]. Our results showed similar OSDI scores (28.6) in a similar health care staff cohort who were wearing face masks for approximately 8 h that OSDI level may reflect evaporative effect of face mask usage, even though we had not a control group of non-mask wearers. Aksoy et al. also reported that 8-h mask use increased the OSDI score, and taping the upper part of the mask decreased the OSDI score [17].

Another entity described in 1986 as an evaporative dry eye reason is “office eye syndrome”: in which air conditioning in the office environment causes a decrease in TBUT time, causing eye irritation and an increase in dry eye symptoms [22]. This entity may have an additional effect on the decrease in TBUT time in this health care staff cohort working in an air-conditioned hospital. However, the likely cause of this situation is that the poor-quality air generated by breathing is blown directly to the ocular surface from underneath the mask which is a closer and continuous source rather than an air conditioning system.

The main limitation of this study is the lack of a non-mask wearer control group. However, the arrangement of this control group is impossible nowadays due to the COVID-19 regulation. Another limitation is the subjective nature of the OSDI score. We believe this study will support further studies with larger study populations that may be planned to compare results during routine use of face masks to a period without face mask usage.

In conclusion, the use of surgical masks throughout the day leads to a significant reduction in NI-BUT, regardless of age, gender, and OSDI score. Prolonged use of surgical masks should be considered as a risk factor for evaporative dry eye disease.