Kalzifikationen von hydrophilen Intraokularlinsen: Entstehung und Morphologie

The aim of this work was to characterize and investigate the formation mechanisms of calcifications of hydrophilic intraocular lenses (IOL). Polymeric intraocular lenses are used to replace the natural lens of the eye in the treatment of cataracts, in which the natural lens of the eye becomes cloudy. Calcification, which occurs mainly with the hydrophilic representatives of these artificial intraocular lenses, causes the lens to become cloudy due to the deposition of calcium phosphate microparticles, necessitating replacement, which must be prevented. In this context, calcification occurs sporadically in all hydrophilic IOLs available on the market (<1%), and in some batches much more frequently. To characterize this phenomenon in more detail, a total of 16 IOLs explanted due to potential calcification were characterized in this study using a wide range of analytical methods. The presence of a calcification was proven in a total of 12 IOLs. The analyses showed that depending on the morphology of the formed microparticles, calcifications have to be differentiated into two classes: The spherical and the dumbbell-shaped class. In the spherical class, depending on the position of the crystallization nucleus relative to the surface, various sub-forms of microparticles can be formed, which can be present individually or mixed. The starting point of calcification here seems to be due to a spatially and temporally unique event. In the dumbbell-shaped class, the microparticles are exclusively arranged in a layer below the surface. Within the layer, 3D tomography was able to detect all growth stages of the dumbbells, starting from a rod as the crystallization nucleus, which speaks here for the continuous formation of the crystallization nuclei. These findings were further deepened by in vitro diffusion experiments on a hydrophilic model polymer. These experiments showed that calcium ions interact with the polymer. Furthermore, in a calcium-alizarin system, the formation of microparticles in layers was observed, which is comparable to the arrangement of microparticles in calcifications.