Diurnal variations of tear film osmolarity on the ocular surface

Abstract

The measurement of tear film osmolarity has been suggested as a gold standard in the diagnosis of dry eye. Many tear film physiological variables oscillate during the day, therefore previous reports have studied how this variable changes throughout the day. The present brief review article will summarize the current clinical knowledge and the main conclusion of the diurnal osmolarity variation in the tear film. For this purpose, the review performs a critical analysis of sample size and characteristics, the differences in the diurnal osmolarity variation on healthy versus altered tear film conditions or environment eyes, and time of day and number of measurements done. A total of twenty-one studies where one of the main objectives was to analyse the variance of the tear film osmolar value along different time points in a day on a human cohort were compared. Osmolar tear film value does appear to be somewhat influenced by the time of day in healthy subjects and patients with ocular surface disease or altered by environmental conditions. Both, healthy and no-physiological tear film stable cohorts, showed variations in results depending on the study: no variations during the day or statistically different values at some point in the day (these differences could be in the middle of the day or between the beginning and the end of the day, with higher values in the morning than in the afternoon, or even the opposite situation). The possibility of diurnal variations in tear film osmolarity should be considered by the clinician since the time of day when the tear film measurements are made can be critical in making the right diagnosis. Future studies in the diurnal variation field may have to use a well-established range of measurement time-points and a larger group of healthy and tear film altered by pathological or environmental conditions subjects.