Abstract
Purpose :
To investigate the predominant mechanisms involved in tear breakup (TBU) in dry eye (DE) subjects and evaluate their effect on corneal detection thresholds to mechanical stimuli.
Methods :
Eight DE subjects were seen for two study visits. Two microliters of sodium fluorescein dye was instilled in the left eye of each subject. Subjects were instructed to keep their eye open for as long as possible, sustained tear exposure (STARE), while a camera recorded fluorescein intensity changes in the tear film. An IU Belmonte esthesiometer delivered mechanical stimuli to the cornea to measure corneal sensory detection thresholds before, after, and 30 minutes after 5 STARE trials. A mathematical model estimated evaporation rate, tear film osmolarity, tangential flow rate, or decaying flow with decay rate from areas of TBU objectively identified using machine learning.
Results :
Image extraction resulted in n=31 usable regions of TBU from 8 subjects. Plots of flow parameters vs evaporation rates for each TBU region reveal tangential flow to be a significant contributor to the majority of TBU regions indicating that evaporation alone is not an accurate representation of TBU. Threshold changes, calculated as thresholds post STARE trials subtracted from baseline thresholds, varied amongst subjects; some subjects appeared to be sensitized while others were desensitized by varying amounts. Mean thresholds for mechanical detection did not change significantly across timepoints (p=0.33). Maximum blink intervals varied amongst subjects, with an average of 19.5 ± 14.7 sec and a median of 12.3 sec ranging from 4.4 to 44.1 sec. Final osmolarity estimates in areas of TBU show increases with increasing evaporation.
Conclusions :
Our results suggest that rapidly developing areas of TBU in DE patients are driven by high tangential flow, presumably due to an unequal distribution of lipids, and not simply evaporation due to a thin lipid layer. Further research is needed to explore mechanisms driving TBU in DE patients to more effectively develop treatments aimed at ameliorating the initiating factors involved in the neurosensory abnormalities characteristic of DE.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.