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Sangly P. Srinivas, Chhavi Gupta, Anuj chauhan; Kinetics of Penetration of Fluorescein into the Rabbit Cornea. Invest. Ophthalmol. Vis. Sci. 2011;52(14):469.
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To model the kinetics of penetration of fluorescein across the cornea.
Rabbit corneas mounted in vitro were exposed to fluorescein at their endothelial surface. Transcorneal fluorescence (ex wavelength = 490 +/- 10 nm; em wavelength = 530 +/- 10 nm) were then obtained periodically for 4 hrs using a custom-built confocal microfluorometer. Such a family of fluorescence profiles was employed to fit a kinetic model for calculation of permeability and diffusion coefficients across the cellular layers and stroma, respectively.
The transcorneal fluorescence profiles exhibited sudden jumps at the stroma-epithelium and endothelium-stroma interfaces, indicating reduced partitioning of the dye into the lipid-rich cellular layers in contrast to the hydrophilic stroma. The stromal thickness was steady for the first 180 min of perfusion but later showed swelling with continued accumulation of fluorescein in the stroma and epithelium. The fluorescence profiles reached a pseudo steady state after ~ 5 hrs. A diffusive transport model which included a term for convective flux into the stroma showed a good fit to the trancorneal profiles at different points. The estimated permeability coefficients for the epithelial and endothelial layers were also close to the reported values but the diffusion coefficient of the stroma was found to be much smaller than predicted by the diffusion cell studies.
The penetration kinetics of fluorescein could be represented sufficiently by a diffusive transport model. Entrainment of the dye with the inward water movement also contributes to the dye accumulation, and needs to be incorporated in modeling the kinetics of fluorescein penetration. The entrainment would be pronounced when the endothelial barrier integrity is lost over time under in vitro conditions.
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