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Chapter 2:
Optical Clearing of Fibrous Tissues
Normally, eye sclera is a turbid medium that is nontransparent in the visible range (see Fig. 7). The origin of scleral spectra formation can be understood on the basis of light scattering by a system of polydispersive irregularly arranged collagen cylinders immersed in the ground substance with a lower refractive index and strong absorption bands. With natural thickness of 0.6-€“0.8 mm, this tissue shows multiple scattering and looks like a white matter. The transition from a multiple to a low-step∕single scattering can be provided by the drying of a tissue sample [Fig. 7(c)] or its impregnation by an immersion liquid. Figure 5 is a schematic representation of the human scleral sample structure and geometry of light irradiation. Analytical approaches for describing the propagation of light in the sclera are valid only when strongly simplifying assumptions are used, which make the model substantially less adequate. Thus, the direct simulation of photon migration in a medium using a Monte Carlo simulation was used for calculating spectral characteristics and photon statistics. The Monte Carlo simulation of the sclera transmission and reflection spectra was carried out using the probability function for the free photon path l. The ordering of scatterers (thin dielectric cylinders) was taken into account, using the experimental radial distribution function g(r) obtained from electron micrographs of human sclera (Figs. 4 and 8).
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