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Richard J Braun, Longfei Li, Nicholas Gewecke, Carolyn G Begley, Peter Ewen King-Smith, Javed Siddique; Tear Film Flows Over the Whole Ocular Surface and in Tear Break-up. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1979.
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© ARVO (1962-2015); The Authors (2016-present)
The purpose of this project is to use mathematical models to visualize tear film (TF) flow while normalizing variables in different ways. The results are compared with experimental images of TF flow and tear breakup (TBU) to better predict local changes in tear film osmolarity and fluorescence during normal flows and in TBU.
Tear films of 10 subjects with a range of tear break-up times (3-45 sec) were simultaneously recorded using retroillumination (RI) and fluorescence at high resolution following the instillation of 2 microliters of 2% fluorescein (FL) dye. Additionally, video recordings of blinks and subsequent interblinks after installation of 1microliter of 5% FL were obtained. Math models were solved for local changes tear film thickness (h), osmolarity (c) and FL (f) concentrations inside the tear film for axisymmetric (circular or spot) breakup. FL concentration was converted to FL intensity I using the expression involving h and the full range of f as described by Nichols et al (IOVS 2012;53:5426--32).
Computed results for I in the flows over the whole exposed ocular surface compare well with video recordings of FL intensity. The supply of new tear fluid was captured. The computed f and c are compared for spot breakup for different evaporation models. The model predicts locally elevated concentrations of osmolarity within areas of TBU as in previous work. The model predicts the FL intensity patterns very similar to the computed thickness and the observed experimental results. We summarize cases where c and f can differ significantly, and where I can deviate from the standard expected pattern which is important in experimental interpretation.
The models, which were developed using close comparisons to experimental data, match well with observed in vivo flows and helps explain dynamics of TF flows and TBU. Differences in dynamics of osmolarity and FL in the spot breakup case are explained.
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