Diurnal variations in non-invasive tear break-up time (NITBUT) and tear evaporation rate (TER) do not appear to exist, according to a study published in Contact Lens and Anterior Eye. However, some tear molecules do show inter- and intra-day variability, and some had a moderate correlation with TER diurnal variation.

Researchers collected data from 17 healthy study participants (mean age 25.1±6.6 years, 10 women) including NITBUT and TER, and collected tear samples for cytokine analysis. They evaluated participants over the course of  1 screening visit and 2 subsequent visits. The team performed assessments once in the morning between 9:00 and 10:00 AM and once during the afternoon between 3:00 and 4:00PM during each follow-up visit.  

Investigators included participants aged between 18 and 40 years who did not wear contact lenses, experience ocular allergies, or use ophthalmic drops within a week of the study. Patients did not use systemic medications known to affect tear production within 30 days of any visit and did not have a history of ophthalmic surgery or active ocular disease.  


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The team observed no significant difference in TER or NITBUT over the course of the study. Out of 15 cytokines investigated, researchers were able to detect 11 in over 50% of the cohort. The researchers did observe significant variations in some cytokine levels including inter-day changes in IL-10 (P =.027), IFN-γ (P =.035) and TNF-α (P =.04) and intra-day differences in IL-8/CXCL8 (P =.034) and MCP-1 (P =.002). They also determined associations between TER and IL1-β, IL-2, and Fractalkine (P =.03, P =.03 and P =.046, respectively) at the first follow-up visit.

“The time of day may have an impact on TER and tear break-up values, as well as on tear molecule levels,” according to the researchers. “Increasing the knowledge in this field is important, as the variation of pro- or anti-inflammatory molecules depending on the evaporation of the tear film could influence the pro-inflammatory status of the ocular surface in some adverse environments.”

Study limitations include a small sample size, significant age differences between the participants, and the inability of researchers to isolate tear evaporation from the skin. 

Reference

Arroyo-de Arroyo C, Byambajav M, Fernández I, et al. Diurnal variation on tear stability and correlation with tear cytokine concentration. Cont Lens Anterior Eye. Published online May 10, 2022. doi:10.1016/j.clae.2022.101705