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Lan Zhong, Deborah Antwi, Richard J Braun, Peter Ewen King-Smith, Carolyn G Begley; Simulation and measurement of Glob-Driven Tear Film Breakup. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4907.
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Tear film thinning and breakup has been shown to occur in areas of thin lipid, presumably due to locally higher evaporation rates. However, tear film break-up (TBU) has also been observed within areas of thicker lipids; so-called glob-driven TBU. This study used mathematical models for evaporative or glob-driven TBU to test the hypothesized mechanisms for TBU observed with fluorescence (FL) imaging of the tear film.
We have previously developed a mathematical models to simulate TBU by these two main mechanisms. For evaporative TBU, with a fixed evaporation profile, we compute the tear film thickness (h), the osmolarity (c) and the FL concentration (f). For glob-driven TBU, we added fixed glob size with an elevated concentration of insoluble surfactant concentration (polar lipids) that drive tangential flow and may cause TBU via the “Marangoni effect.” Computed f and h values were used to compute FL intensity I. Modeling of TBU was compared to fluorescence imaging of the tear film from 25 subjects, who kept one eye open as long as possible (after instillation of 5 µL of 2% FL) to induce TBU. TBU instances with simple geometry were identified for comparison with the mathematical models computed using custom MATLAB programs.
The case shown in Figures 1 and 2 compares mathematical modeling to experimental data for rapid TBU of a spot from the inferior temporal cornea of one subject. The round shape of the TBU suggests using the axisymmetric spot model for TBU. Fig 1 shows results for normalized I from both experimental data and theory. The initial f was f0=0.22%, the initial h was assumed to be h0=3.5μm; we also assumed the glob size was 0.0752mm, a unifrom evaporation rate of 15μm/min was included. TBU can be observed in about a second (2.23s), with similar results in both experiment and theory. Fig 2 shows the minimum I from the math model and experiment. Again, the comparison is good. More cases including different TBU mechanisms will be given in the poster.
These results demonstrate that TBU predicted from theory has appropriate time and length scales when compared with selected experimental results. More complex TBU shapes will be the subject of future work.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Fig 1: Normalized I form experiment and theory
Fig 2: Minimum I from both experiment and theory
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