Hydroxyapatite formation on implanted hydrogel intraocular lenses.
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Biomedical subjects
A K Yu
Publications and source records attributed to A K Yu.
Clinical features of 46 eyes with calcified hydrogel intraocular lenses.
PURPOSE: To clarify the clinical features of delayed calcification of hydrogel intraocular lenses (IOLs) based on observation of a large case series. SETTING: Ophthalmology department of 2 university teaching hospitals, Hong Kong, China. METHODS: The first 44 patients with a known diagnosis of calcified IOL were recruited. Medical and ophthalmic histories were obtained. Surgical details, surgical complications, and visual acuity before and after IOL implantation were also retrieved. Patients then had a visual acuity test, a slitlamp examination of the features of the IOL calcification, and a fundus examination for clarity of view. RESULTS: Forty-six eyes of 44 patients had IOL calcification. All had a Hydroview IOL. The onset was from 4 to 26 months after surgery. Ninety-three percent of eyes had generalized IOL calcification, and 96% had forceps marks on the IOL. Mean visual acuity deteriorated from 0.4 at 3 months to 0.13 at 19 months. Visual loss was more severe in patients with diabetes mellitus or ischemic heart disease and in those in which the IOL calcified earlier after implantation. CONCLUSION: All cases of IOL calcification were delayed in onset. The presence of forceps marks may provide a clue to the pathogenesis. Bilateral but asymmetric involvement in 2 patients suggests that the IOL was involved in the pathogenesis. Affected patients lost an average of 2.8 Snellen lines of visual acuity. Some eyes progressed more rapidly; however, the modulating factors remain unknown.
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Measurement and control of interface strength of RF magnetron-sputtered Ca-PO coating on Ti-6Al-4V substrates using a laser spallation technique.
In previous studies, an RF magnetron sputter technique was developed for the production of thin calcium phosphate coating. Several deposition parameters were found to influence the growth rate and the stoichiometry of the coatings. For instance, deposition with additional oxygen pressure decreased the Ca to P ratio of the coatings to 1.67. For application of these coatings on actual Ti implants, it is important to know their adhesive tensile strength with the implant surface and how it varies with the deposition parameters. Motivated by these goals, the aim of this study was to measure the adhesive tensile strength of these coatings with Ti substrates and to study its variation with the deposition parameters. Since most mechanical characterization methods are incapable of providing a direct measure of the interface's fundamental strength, a novel laser spallation experiment was used to accomplish this task. In this experiment, a compressive stress pulse is generated on the back side of a substrate by impinging a 3-ns long Nd:YAG laser pulse. The stress pulse propagates through the substrate and is reflected into a tensile stress wave from the free surface of the coating deposited on its front surface. The returning tensile pulse pries off the coating if its amplitude is high enough. The peak interface tensile stress is computed by using the optically recorded free surface displacement of the coating. Because interface decohesion is accomplished at a strain rate of almost 10(7) s-1, all inelastic processes essentially are suppressed and the measured value essentially is the intrinsic tensile strength of the interface. Tensile strength values in the range of 500-900 MPa were recorded for the interfaces between sputter-deposited calcium-phosphate coatings and Ti substrates. To confirm the locus of failure, the spalled spots were examined using SEM and EDS. The variation in the measured values was related to the changes in the deposition conditions.
Alloys↗
Opacification of artificial intraocular lens: an electron microscopic study.
This paper describes the usefulness of electron microscopy in the investigation of the cause of opacification of an intraocular artificial lens (IOL), which affected both the anterior and posterior surfaces of the IOL. The explanted lenses were remarkably similar and were uniformly opaque, with "reticulated" surfaces under dissecting and ordinary light microscopes. TEM showed that the surfaces of the explanted lenses were irregular, and there was a layer of electron-dense granular deposits that extended to a depth of approximately 5 microm into the lens substance. SEM showed a "cerebriform" lens surface with elevated areas alternating with depressed crevices, which corresponded nicely to the TEM appearance. Energy-dispersive x-ray analysis showed that the deposit was composed of calcium, oxygen, and phosphorus, which was later shown to be calcium hydroxyapatite by x-ray diffraction study. Electron microscopy has proven to be an essential tool in the investigation of the cause of this mysterious outbreak of opacification of the surfaces of the artificial lenses. Apart from directly visualizing the lens surfaces in a 2- and 3-dimensional manner, it also provides information on the elemental composition of the deposit. Such findings enable the clinicians and manufacturer to search for the underlying pathogenesis of the abnormal calcium hydroxyapatite crystals deposit.
Calcinosis↗