Abstract
Purpose :
The purpose of this study was to compare measurements of the lipid layer thickness (LLT) of the tears when taken at different times of the day.
Methods :
A custom built instrument, a stroboscopic video color microscope (SVCM) was used to measure the lipid layer of the tears. The instrument measures LLT of a circular area 6mm in diameter, taking 22 images/sec at 1,400x1100 pixels. Over the course of 40 seconds, 900 frames are recorded. Software analyzes the data and blink disruption of the data is deleted. The LLT over the lower third of the circular area was calculated.
35 subjects participated. For each subject, a baseline measurement was taken and processed. The subject returned for two more LLT measurements on separate days. Appointments were scheduled at any time during a normal workday, with the earliest measurement occurring at 8:33 am and the latest measurement being taken 5:39pm. Subjects were told not to rub their eyes or use any eye drops on the day of each measurement. The eye with the thinnest LLT at the initial baseline visit was used for analysis.
Results :
105 LLT measurements were used. The mean LLT was 49.53±10.98 nm. These data were analyzed using a single factor repeated measures analysis of variance (ANOVA). The effect of time was not significant (p=0.19). Regression of LLT versus time yielded a correlation coefficient of 0.0 (p=0.619).
To account for potential bias between subjects due to variations in the time of day in which measurements were taken, a second group of analyses using the change in time from the earliest measurement and the associated change in LLT was performed. The mean and standard deviation of LLT changes was calculated for changes of time less than one hour (-2.50±11.09 nm), changes of time of 1-2 hours (-0.24±11.93nm), and changes of time over 2 hours (-0.25±9.56nm). Repeated measures ANOVA was performed. The change in time had an insignificant effect on the change in LLT (p=0.582). Regression of LLT change versus time change yielded a correlation coefficient of 0.0 (p=0.955).
Conclusions :
These data suggest that lipid layer thickness for a given subject is consistent over the course of a typical work day. With many studies currently on going in the treatment of dry eye, it is important to rule out confounding causes of change in LLT. This study suggests that the time of day is likely not a confounding variable in these studies of lipid layer thickness.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.