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In vitro high frequency ultrasonic characterization of colonization of microporous polymer used to support artificial cornea

High frequency ultrasound has been widely used in ophthalmology to measure ultrasonic properties and thickness of tissues of the anterior segment of the eye. However, specific applications such as biointegrable keratoprosthesis (artificial cornea) control have not yet been reported. Keratoprosthesis has been developed as an alternative treatment to human cornea transplantation. The keratoprosthetic device consists of an optical system supported by a biocolonizable microporous polymer which is implanted in the damaged cornea. The polymer (200 microns thick, 50 microns pore size) is integrated into the recipient cornea through the progressive penetration (colonization) of the corneal cells into the pores of the polymer. The purpose of this work is to assess the polymer colonization and integration into the corneal tissue using high frequency ultrasound imaging and characterization. Polymer implantation was performed in rabbit cornea and a backscatter ultrasound microscope operating at 50 MHz (30 microns axial resolution) was used to acquire in vitro signal backscattered by the polymer and the surrounding corneal tissue 3 days, 10 days, 2 months, 70 days and 6 months after implantation. The frequency variation of the apparent acoustic backscatter and the apparent integrated backscatter were measured. Measurements were correlated with histologic data which established the level of cellular ingrowth and cell density in each specimen.