Daytime Variations of Tear Osmolarity and Tear Meniscus Volume

Abstract

Objectives To determine the pattern of variations in tear osmolarity and tear meniscus volume in dry eye patients and in healthy control subjects over an 8-hour daytime period. Methods Ten normal subjects (5 males and 5 females with a mean age of 27 ± 7 yrs) and 10 dry eye patients (4 males and 6 females with a mean age of 36 ± 12 yrs) who had been diagnosed on the basis of having an ocular surface discomfort index (OSDI) >12 and a tear breakup time of < 10 seconds or Schirmer’s test score of < 5 mm were included. The tear meniscus volumes of the participants were measured using ultra-high resolution optical coherence tomography (OCT), and tear osmolarity was measured using the TearLab Osmolarity System. Both measurements protocols were conducted on the right eye of each participant every two hours beginning at 8:30AM and ending at 4:30PM. 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 hours, 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.

Basal values, intra-day and inter-day variations in tear film osmolarity and tear fluorescein clearance

“…This result agreed with that of Webber et al 61 who using fluorophotometry and reported that the morning tear turnover rate was higher than the afternoon rate in healthy subjects, which suggested a circadian rhythm in tear flow, and which also was suggested for aqueous tear evaporation, 62 tear meniscus height, 54 and tear film stability, 63 tests that might be related to the T-FCT results. Also, it has been found a daily variation of visual function, keratitis, conjunctival hyperemia and symptoms in DED subjects.…”

“…53,54 Li et al 54 recently reported diurnal variations in tear osmolarity and found that osmolarity was unaffected by the time of day in normal subjects.…”

Diurnal Pattern of Tear Osmolarity and Its Relationship to Corneal Thickness and Deswelling

“…These results are consistent with freezing point depression 9 and microosmometric 18 studies that found hypoosmotic tears upon awakening. Our TO is also consistent with the normal average TO of 301.8 6 10.5 mOsm/L reported by TearLab 13a and Li et al 19 who reported normal daytime TO of 298.0 6 14.2 mOsm/L also measured by TearLab Osmometer with a similar subject mean age of 27 6 7 years. Of interest, the results from our study support the hypothesis that normal eyes have a robust homeostatic system, which maintains a stable tear film in response to ordinary environmental stresses over waking hours.…”

Assessment of corneal thickness and tear meniscus during contact-lens wear

“…Naked eye (i.e., no contact lens) TMV values obtained here are similar to those provided by García-Lázaro et al [45] (1.35 ± 1.18 L). However, the values of LTMV obtained by Li et al [46] are quite lower than ours. They determined TMV (both upper and lower) over 8-h period.…”