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22 May 1995 Scattering of ocular tissues and polymers
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Ocular tissues are mainly made up from conjunctive fibers on the basis of collagen. The way they are arranged as well as the proportion of water contained in the tissues determines their transparency. As example the fibers in the sclera have diameters between 30 and 300 nm and are arranged in ribbon-like fiber bundles (15 microns thick and 140 to 150 microns wide) that cross each other in all directions [1]. Both different diameters and interlaced structure lead to a tissue displaying scattering properties. By opposition the cornea scatters visible light in a much lower amount, mainly because it is up from fibers having diameters varying only between 19 and 34 microns and that are organized in a parallel fashion within layers. Such a structure is of primary importance when objects have to be imaged through such tissues because scattering results in a blur of the image obtained. Therefore, any irregular change in the structure due to anarchical growth or in diameter as it may be the case with ageing of the crystalline lens results in a loss of visual acuity. The use of biocompatible materials has tremendously increased in ophthalmology during the last years. PMMA still represents the majority of the intraocular lenses replacing the refractive power of the crystalline lens. Viscoelastic materials are currently utilized in the anterior chamber and perfluorocarbons or other polymers like polydimethylsiloxanes (PDMS) are used as vitreous substitutes. The physical properties of such materials should be similar to those of the tissue they replace. Consequently, whenever possible flexible materials that mimic ocular tissues are developed in order to minimize local stress and tissue deformation. Among them, gels that consist of a network crosslinked in a balanced salt solution (BSS) have also been tested as intracorneal implants for GIAK (gel injection adjustable keratoplasty), a technique designed to correct myopia [2]. Because the number of intermolecular bonds per linear chain governs the rigidity of the material, various collagenous tissues can be mimicked by controlling both concentration of the network and the degree of crosslinking. However, when such materials are implanted within the optical path of the eye, their optical properties should be scrutinized. A high transparency is necessary in the visible part of the spectrum (450-700nm), associated with a high absorption in the UV and the deep blue part (400-450nm) for protection of the retina and the crystalline lens. In addition, scattering should also be minimized to avoid loss of visual acuity. Therefore, apart from an accurate shape and refractive index, the surface quality and the homogeneity of the implants have also to be as high as possible. The purpose of this study was to compare the scattering of such materials to that of ocular structures.
© (1995) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Pascal O. Rol, Dominik Beck, Valerie Jallet, and Jean-Marie A. Parel "Scattering of ocular tissues and polymers", Proc. SPIE 2393, Ophthalmic Technologies V, (22 May 1995);

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