Daytime Variations of Tear Osmolarity and Tear Meniscus Volume

Objectives: The aim of this study was to determine the pattern of variations in tear osmolarity and tear meniscus volume in patients with dry eyes and in healthy control subjects over an 8-hr daytime period. Methods: Ten normal subjects (5 men and 5 women with a mean age of 27 +/- 7 years) and 10 dry eye patients (4 men and 6 women with a mean age of 36 +/- 12 years) who had been diagnosed on the basis of having an ocular surface discomfort index >12 and a tear breakup time of <10 sec or Schirmer test score of <5 mm were included. The tear meniscus volumes of the participants were measured using ultrahigh resolution optical coherence tomography (OCT), and tear osmolarity was measured using the Tear-Lab Osmolarity System. Both measurements protocols were conducted on the right eye of each participant every 2 hrs beginning at 8:30 AM and ending at 4:30 PM. The OCT imaging was performed first and was followed by osmolarity testing. Results: The mean tear osmolarity of the dry eye patients was 304.0 +/- 10.8 mOsm/L, and the mean tear osmolarity of the normal subjects was 298.0 +/- 14.2 mOsm/L (P>0.05). Over the course of 8 hrs, the average measured osmolarities of the dry eye group varied by approximately 21.9 +/- 13.5 mOsm/L (range, 6-43 mOsm/L), and the average measured tear osmolarities of the normal group varied by approximately 21.0 +/- 9.2 mOsm/L (range, 8-35 mOsm/L). At 2:30 PM, the average volume of the tear menisci in the dry eye group was significantly lower than that of the subjects in the normal group (P<0.05). No correlations between the tear meniscus volumes and tear osmolarities of either group were observed. Conclusions: Variations in the tear osmolarities of individual dry eye patients and healthy normal control subjects were documented over the course of 8 daytime hours. No relationships between tear osmolarities and tear meniscus volumes were observed.