Abstract
Purpose :
To assess noninvasive tear film parameters describing the post blink tear film leveling (TFL), tear film surface regularity (TFSR) and breakup time (NIBUT) in the winter and summer season of Central Europe (continental climate) in a group of healthy subjects.
Methods :
30 healthy young subjects aged (mean±SD) 24.4±1.5 years were measured between November and March as well as between May and August. NIBUT was subjectively assessed by indicating the first visible deformation of Placido rings recorded at 13Hz by videokeratoscope (Medmont) whereas interblink TFSR and TFL were recorded in natural blinking conditions with lateral shearing interferometer at 25Hz. Tear film parameters were averaged from three consecutive measurements. Symptoms were assessed with OSDI questionnaire. During each visit, office temperature (T) and air relative humidity (RH) were measured and the hours of sleep recorded. Additionally, during the first visit in winter, fluorescein breakup time (FBUT) and tear osmolarity were assessed. The hypothesis of normal distribution was not rejected for all the data.
Results :
Mean FBUT was 15.9±6.6s, osmolarity 298.3±6.9mOsm/L and OSDI 8.8±8.9. Seasonal statistically significant differences (paired t-test) were observed in several parameters: RH changed on average from 26.0±5.8% to 58.3±4.9%, P<0.001, NIBUT changed from 13.4±6.8s to 16.6±6.2s, P=0.013, and TFSR changed from 84.5±5.3a.u. to 81.7±3.2a.u., P<0.001. There were no differences in TFL, P=0.182, OSDI, P=0.473, sleeping hours, P=0.102, and T, P=0.185. Fig. 1 shows TFL for healthy eyes in summer and winter in comparison to the TFL retrospective results for a dry eye group (n=33) acquired at different seasons and presented at ARVO 2023 (IOVS,64:684).
Conclusions :
The regularity of the tear film surface, here expressed by TFSR, depends on the season. This may lead to shorter tear film stability and, consequently, shorter NIBUT in winter. However, the post blink TFL, which, as previously shown, differs significantly in the dry eye group compared to healthy eyes, does not change with the season in the healthy group. Thus, faster distortion of the tear film surface (i.e., shorter NIBUT and higher TFSR) may result from greater evaporation due to lower humidity in winter, but with no corresponding changes in the dynamics of the lipid layer (TFL).
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.