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 main conclusion of the diurnal osmolarity variation in the tear film. For this purpose, the review performs a critical analysis on 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 statistical 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 wellestablished range of measurement time-points and a larger group of healthy and tear film altered by pathological or environmental conditions subjects. Van Setten 52Daily variation in osmolarity, maximal amplitude of osmotic variation, frequency of osmotic cycles, the level of osmolarity at which the variation does occurs could be the main factors that further characterize osmokinetics.Small sample analysed; wide time range stablished on time-point

Cysteamine Eye Drops in Hyaluronic Acid Packaged in Innovative Single-Dose Systems, Part II: Long-Term Stability and Clinical Ocular Biopermanence

“…In addition, although environmental conditions were controlled and maintained, it would be ideal to carry out the study in a chamber that maintains constant temperature and humidity conditions for all individuals and days of the study. On the other hand, the effect of diurnal tear variations has been reduced as much as possible by conducting the bioavailability study between 9 a.m. and 12 a.m., which is one of the greatest strengths of this work based on previous publications [32][33][34]. Another limitation of the present study is that the clinical study was carried out in healthy volunteers, although it would be ideal to perform it in patients diagnosed with cystinosis.…”

“…The inclusion and exclusion criteria are listed in Table S1 of the supplementary material. To mitigate the influence of diurnal variations in tear parameters or interexaminer influence, all measurements were conducted within the same time window (09:00-12:00 a.m.) by the same investigator across all sessions and patients [32][33][34], and with environmental conditions controlled and maintained under similar conditions of temperature (20-23 • C) and humidity (50-60%). The study protocol adhered to the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board/Ethics Committee of the Ethical Committee of Clinical Research of Galicia (2019/204).…”

Evaluation of therapeutic efficacy of Emustil drops for ocular discomfort and tear film osmolarity using different treatment management modes under dry environmental conditions

“…Despite studies indicating that osmolarity is not effective in distinguishing between dry eye types [ 35 ], tear hyperosmolarity is still one of the operative diagnostic tools for DED [ 36 ]. The tear osmolarity value in the dry eye is higher when compared with normal eyes [ 37 ]. Investigations have been done to determine the cut-off value of normal tear osmolarity.…”