Purchase this article with an account.
Richard Braun, Carolyn Begley, Adam Winkeler, Peter King-Smith, Javed Siddique; Mathematical Modeling of Tear Break-up and Fluorescent Intensity. Invest. Ophthalmol. Vis. Sci. 2013;54(15):949.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The local mechanisms involved in the formation and development of areas of tear breakup (TBU) remain poorly understood. The purpose of this project is to develop mathematical theory for variables of interest to compare with experimental images of TBU to better predict local fluctuations in tear film osmolarity and fluorescence (FL) during and following TBU.
Tear films of 10 subjects with a range of tear break-up times (3-45 sec) were simultaneously recorded at high resolution following the instillation of 2 microliters of 2% fluorescein. Using these images, which were aligned by the center of the pupil, as input, math models were solved for local changes tear film thickness (h), insoluble surfactant concentration (representing the lipid layer and affecting evaporation), as well as osmolarity (c) and FL (f) concentrations inside the tear film. FL concentration was converted to fluorescent intensity I using the expression involving h and the full range of f as described by Nichols et al (IOVS 2012;53:5426--32).
Theoretical results show that elevated surfactant concentration or evaporation rate led to thinner regions where TBU first occurs. Figure 1 shows results for h, c & I (in the plots, x is location in space and t is time) with evaporation at 2.5 microns/min from the initially 2 micron film surface and osmosis from the cornea; a single breakup regions (blue) is shown. The model predicts locally elevated concentrations of osmolarity within areas of TBU (red). The model predicts the FL intensity patterns very similar to the computed thickness and the observed experimental results (Figure 2: color contour plot). For the rate of osmosis from the cornea in the displayed results, the osmolarity increases to 2.4x the isosmolar value, or 720 mOsm. The sensitive dependence of this result on the corneal permeability will be studied. Quenching of the FL is captured as well.
This model, which was developed using experimental data from subjects with a range of tear film instability, explains dynamics of areas of TBU and predicts local increases in osmolarity and the dynamics of fluorescent intensity in areas of TBU.
This PDF is available to Subscribers Only