Intraoperative Pachometry During Automated Lamellar Keratoplasty: A Preliminary Report
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ABSTRACT BACKGROUND: The hinge technique greatly improves the results of automated lamellar keratoplasty but makes it impossible to measure the thickness of the corneal cap with a micrometer. We developed a technique of measuring cap and stromal disc thickness with a pachometer and compared the results with those obtained with a micrometer. METHODS: Measurements of the thickness of the stromal disc and/or corneal cap were taken with the Mitutoyo micrometer and the Chiron ComeoGage System III pachometer in five myopic and three hyperopic cases undergoing automated lamellar keratoplasty with complete cap resection. The intended postoperative refraction was piano. Postoperative refractions were taken at two months. RESULTS: In most cases, the corneal cap measured thinner while the stromal disc measured thicker by the micrometer than by the pachometer because of the hydration status of the stromal bed. In both myopic and hyperopic cases, the thickness measurements taken with the pachometer correlated better with the postoperative spherical equivalent values than those taken with the micrometer. CONCLUSIONS: The thickness measurement of corneal resections by both micrometry and pachometry is greatly influenced by tissue hydration status. When hydration is similar, the pachometer provides more accurate thickness readings than does the micrometer, as determined by correlations with intended refractive results. (Refract Corneal Surg. 1994;10:41-43.)Keywords:
Micrometer
Morphology
Misorientation
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EFFECTS OF LAMELLAR SPACING ON THE CREEP BEHAVIOR OF A CAST TiAl ALLOY WITH FULLY LAMELLAR STRUCTURE
Fully lamellar microstructures of TiAl alloy with the identical grain sizes and three different lamellar spacings were obtained by the different heat treatment, and the effects of the lamellar spacing on the creep behavior of the TiAl alloy with fully lamellar microstructures were investigated at the conditions of T=800℃ , σ=205MPa. The results showed that the primary creep and minimum creep rate increased with the increase of the lamellar spacing. Dislocations can be detached from the lamellar interfaces and thus contribute to the creep deformation, and, on the other hand, the interfaces can inhibit the multiple generation of dislocation loops and restrict their motion.
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Microstructural changes of a near fully lamellarγ-TiAl base alloy after heating shock and ageing treatment have been investigated.After infrared heating treatment,the coarse and fully lamellar (FL) structure (lamellar cluster size 300μm,lamellar spacing 1.3μm) of as-castγ-TiAl base alloy became a substable structure with extreme fine lamellar spacing (140 nm) as well as flat lamellar boundaries which could be transformed to a stable,fine,fully lamellar microstructure (lamellar cluster size 40μm) after 1260℃,6 h ageing treatment.
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Objective To study the biocompatibility of acellular cornea stroma implanted in rabbit cornea stroma. Methods The cornea stroma was obtained from adult hog, cells and immunogenic component were removed through different extraction methods, and the elastic and collagen fibers were preserved. Stromal disc with 4 mm diameter was implanted into interlamellar stromal pocket and followed up until 3 months. The immunoreaction of stromal disc was observed with HE staining at different time points. Results The advers immunoreaction was not found in the stromal lamella during experiment and followup. After implantation in 2 weeks, acellular cornea stroma become transparent; after implantation in 3 months, the rabbit stroma cells immigrated into the xenograft, the acellular cornea stromal were gradually degraded. Conclusion It demonstrates that the acellular cornea stroma processes excellent histocompatiblility, thus it is a good materials for constructingtissue- engineered cornea.
Biocompatibility
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The effect of heat treatment on the microstructures and tensile properties of a powder metallurgical (PM) TiAl based alloy has been investigated in this paper. The near gamma (NG) microstructure is transformed to a full lamellar (FL) microstructure with an average grain size of 100 μm by heat treatments. The lamellar spacing of FL structure decreases with the increase of cooling rate. For cooling rates of 5, 10 and 50 °C/min, the lamellar spacing is 1.9, 1.0 and 0.8 μm respectively. The room temperature tensile properties exhibit an increasing trend with decrease of lamellar spacing.
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It is important to control the lamellar spacing of fully la mellar TiAl alloy for improving its mechanical properties. The factors affecting the lamellar spacing of fully lamellar TiAl alloy and the dependence of the lam ellar spacing on the factors were investigated by means of OM and TEM. The resul ts show that the lamellar spacing depends on cooling rate and Al content. The la mellar spacing is inversely proportional to cooling rate and increases with the increase of Al content. At the same time, a theoretical expression of the lamell ar spacing of fully lamellar TiAl alloy during continuous cooling has been deriv ed on the basis of the ledge mechanism of lamellae growth. The theoretical resul ts are in agreement with the experimental findings.
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Microstructure stability in fully lamellar (FL) structure TiAl based intermatellics have been studied. The experiment results have shown that the smaller the lamellar spacing is, the more instable the lamellar structure is. The distinct lamellar spheroidization occurs at 1150°C holding for 24h. This phenomena may be caused by lamellar coarsening and decomposition. The linear residual β phase distributed in the Ti -47 A 1-2 Cr -2 Nb alloy may prevent lamellar spheroidization and improves the stability of lamellar structure significantly.
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