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Rayanne A Luke, Richard J Braun, Tobin Driscoll, Deborah Awisi-Gyau, Carolyn G Begley; Parameter Estimation for Mixed-Mechanism Tear Film Thinning. Invest. Ophthalmol. Vis. Sci. 2020;61(7):350.
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© ARVO (1962-2015); The Authors (2016-present)
Etiologies of tear film breakup (TBU) include evaporation-driven, divergent flow-driven, and a combination of these two. A mathematical model incorporating evaporation and lipid-driven tangential flow is fit to fluorescent (FL) imaging data (Zhong et al., BMB 2019, 81:39-80). The lipid-driven motion is hypothesized to be caused by localized excess lipid, or “globs.” TBU quantities such as evaporation rates and tangential flow rates cannot be directly measured during breakup. We determine such variables by fitting mathematical models for TBU and the computed FL intensity to experimental intensity data gathered in vivo.
We select intermediate cases of TBU, where breakup occurs between 1 and 8 seconds, to be fit with our model for circular (spot) or linear (streak) breakup. Parameter estimation is conducted via least squares minimization of the difference between experimental data and computed answers using the Levenberg-Marquardt method. Theoretical intensity dependent on TF thickness and FL concentration was based on Nichols et al. (2012, IOVS, 53:5426). We fit FL intensity data recorded from 25 normal subjects with 20 trials taken over two visits. The initial film thickness and FL concentration were estimated by separate procedures (Wu et al., IOVS 2015, 56:4211). Subject data extracted along a line at each time level was used to optimize three parameters: thinning rate, v, glob width, xI, and change in surface tension, (Δσ)0. All computations are via custom Matlab programs.
We determine best-fit parameters for mixed-mechanism TBU with several choices for the evaporation profile: zero, uniform, and high under the lipid glob, zero outside. The fits are significantly better for the cases with nonzero evaporation; we interpret this as strong evidence the TF thinning is partly driven by evaporation. An example fit is shown.
Best-fit determination of TBU parameters supports the notion that evaporation and divergent tangential flow can cooperate to drive breakup. The resulting TBU is typically faster than purely evaporative cases. Many instances of TBU may have similar causes, which suggests that interpretation of experimental results may benefit from considering multiple mechanisms.
This is a 2020 ARVO Annual Meeting abstract.
Streak TBU intensity as a function of radius x is fit with a linear model for FL intensity. Optimal parameter values are v = 34.3 μm/min, XI = 0.133 mm, and (Δσ)0 = 2.58 mN/m.
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