Abstract
Purpose :
According to the TFOS DEWS II definition of dry eye (DE), tear film instability plays an etiological factor in DE. We determine quantities in areas of thinning and/or TBU from in vivo fluorescent (FL) intensity videos of the tear film (TF). We optimize parameters in mathematical models of TBU to deduce the strengths of mechanisms in each instance and the resultant stimulus to the ocular surface.
Methods :
FL intensity data was recorded from 8 DE subjects in 5 trials taken in each of two visits. We extracted experimental FL values at the centers of thinning or TBU regions identified manually. The data were fit to ordinary differential equation models using parameters representing evaporation rate (v), tangential flow parameter (b1) and flow decay rate (b2). A least squares minimization of the difference between experimental and computed intensities determined the parameters. Initial FL concentration and localized film thickness were estimated as in previous work (Wu et al IOVS 2015, 56:4211[BR3]) and previous non-DE subject data (Driscoll et al MAIO 2023, 5:1-36) were compared to the new results. All programs were custom-written in Python, Julia and Matlab.
Results :
Extraction resulted in N = 31 instances of TBU/thinning from 8 DE subjects. Evaporation rates lie near previously reported experimental ranges. Findings include: (i) The population of DE subjects exhibited a range of mechanisms active in thinning and TBU. (ii) Individual subjects exhibited different mechanisms in different TBU instances, even within a single trial. (iii) Individual DE subjects had mechanisms overlapping with non-DE subjects, though details varied by subject (Fig 1). (iv) Tangential flow seemed more prominent in this sample than for the non-DE subjects (Fig 1). (v) Osmolarity increases with increasing evaporation at a less than linear rate (Fig 2).
Conclusions :
Mathematical modeling of intensity decay in TBU areas suggests that tangential flow is a prominent mechanism in the TBU of DE subjects, although evaporation also plays a role. Further research is needed to better understand the mechanisms impacting tear film instability in DE subjects.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.