Tear Molecular Composition May Experience Diurnal Variations

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.  

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