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At least 991 records · Page 55Linked to original sources
PubMed1992

Practical aspects of a corneal topography system.

We used the EyeSys Corneal Topography System to examine several issues relating to corneal topography systems and the interpretation of their results. Interferometry measurements of EyeSys calibration spheres indicated that they deviated from suggested values by 0.05 +/- 0.13 D (mean +/- 1 standard deviation). The EyeSys unit reliably determined the calibration spheres to be spherical with differences between the flat and steep axis of 0.10 +/- 0.09 D. The data for the 3 mm chord circle was the least reliable. The spherical equivalent values for the calibration spheres were constantly greater than the 0.25 D reproducibility suggested by the manufacturer. Furthermore, the precision of the outputted values (0.01 D) is beyond the capability of the instrument. This gives the impression that the topography unit cannot consistently reproduce measurements of the calibration objects or chrome plated steel spheres. Image centralization and focus were found to be critical in obtaining accurate results. A target off center by more than 0.25 mm resulted in unreliable data; increasing the focal distance by greater than 1 mm beyond the focal point resulted in a sharp decrease in accuracy (a decrease in the focal distance was even more critical). When measuring aspheric contact lenses, it was found that the keratometer and EyeSys unit provided a close approximation of the surface characteristics of the lenses. A realistic view of the limitations of the topography system being used is critical for proper interpretation of the data.

Calibration↗
PubMedDate not supplied

Preliminary 3-dimensional surface texture measurement and early loading results with a microtextured implant surface.

PURPOSE: This investigation was conducted to obtain preliminary roughness data on a microtextured implant surface and to determine its ability to sustain a 1-stage surgical procedure and early full occlusal loading of single-tooth restorations in humans. MATERIALS AND METHODS: Three-dimensional (3D) vertical scanning interferometry was conducted on samples of the test surface (MTX) and 2 control surfaces (Osseotite and sandblasted/acid-etched [SLA]). Test implants were also placed in vivo, restored with fully occluding single-tooth restorations (n = 27) after 2 months of nonsubmerged healing, and clinically monitored for 48 months of follow-up. RESULTS: Microtexture was relatively uniform on the test surface and more random and irregular on the control surfaces. MTX and Osseotite were similar in some roughness parameters, but the MTX surface had a greater number of micropits that were spaced closer together (Stylus Y lambda q) and with higher slope values (Stylus Y delta q). Cumulative life table results were 100% for all MTX implants placed in maxillary and mandibular jaw locations, and no discernible marginal bone changes were observed. Overall implant success was 100% after 4 years of clinical functioning. DISCUSSION: The findings of this study appear promising but should be considered preliminary, because of the limitations in the number of locations measured on each product sample and the small number of implants clinically studied. CONCLUSION: Within the scope of the present study, MTX implants exhibited a uniform micropitted surface, as well as 100% survival and 100% clinical success after nonsubmerged placement, early loading with single-tooth restorations at 2 months, and 48 months of clinical functioning. (More than 50 references.)

Acid Etching, Dental↗
PubMed2004

[Comparison of ultrasound and optic biometry with respect to ocular refraction after cataract surgery].

In the prospective study of 56 patients with cataract (67 eyes) the authors compared axial length biometry) regarding to postoperative refraction of the eyes. Dioptric power of the intraocular lens (IOL) was determined by SRK II. formula. The difference between predicted and actual postoperative refraction in the spherical equivalent were compared 3 months postoperatively. Axial length measured by ultrasound differed significantly from the axial length measured by optical biometry (p = 0.016). Dioptric power of IOL calculated according to the axial length measured by ultrasound was significantly different from the dioptric power of IOL calculated according to the axial length measured by optical biometry (p = 0.003). The difference between predicted and actual postoperative refraction was not statistically significant (p = 0.384) even if we considered both type of measurement. In conclusion, we found partial coherence interferometry was an accurate and reproducible method for measurement of axial length of the eye before cataract surgery. In the cases of advanced dense cataracts backup of ultrasonic biometry is still necessary.

Cataract↗
PubMed2004

[Mechanisms of the development of anemia in stomach cancer].

Structural and metabolic statuses of erythrocytes were evaluated using cytophoto- and interferometry, fine-layer chromatography, scanning and transmission electron microscopy, electrophoresis and fluorescent probing in 48 stomach cancer patients. Structural and metabolic disorders were detected in mature erythrocytes in patients with and without anemia. Changes in the structure and metabolism of peripheral blood erythrocytes taking place prior to quantitative changes were identified. Anemia development pathways were dependent on enhanced hemolysis of circulating erythrocytes and influx of immature cells from the bone marrow. The changing statuses of the membranes and metabolism appeared to play quite a role in erythrons being damaged by tumor process. Dysfunctional erythrocytes of stomach cancer patients need to be corrected by membrane-stabilizing and -repairing drugs.

Adult↗
PubMed2004

Glass-fiber frameworks for fixed partial dentures: laser-interferometrical in vitro analysis.

OBJECTIVES: Laboratory tests confirmed superior physical properties of fiber-reinforced resin composites; however, clinical failures continue to be observed. This in vitro study introduces a new method to measure strain and fracture resistance in glass fiber-reinforced pontics. METHOD AND MATERIALS: Thirty standardized pontics in five groups were fabricated. Pontics were reinforced with: glass fiber (group 1); glass-fiber bundle surrounded by glass-fiber mesh (group 2); glass fiber with glass-fiber mesh parallel to the pontic's occlusal surface (group 3); or glass-fiber mesh parallel to glass-fiber bundle (group 4). Unreinforced resin composite pontics served as controls (group 5). A laser interferometer measured inner strains (microm/mm) in sectioned pontics, occlusally loaded with 250 N and 450 N, with a universal testing machine. Inner strains were measured on three levels (1, 2, and 3). Specimens were then loaded to crack onset, and loads were recorded. Comparisons were made using analysis of variance. Kruskal-Wallis and Fisher's exact tests were used, respectively, for nonparametric and categorical data. RESULTS: Group 3 showed significantly lower mean strain values than controls. No significant differences in maximal inner strain values or crack onset loads were recorded. The framework of Group 3 inhibited crack propagation significantly better than that in groups 2 and 5. CONCLUSION: Within the limitations of this study, speckle interferometry proved to be a promising method for analyzing strains of pontics under load. The tested framework designs in this study had only limited influence on load-to-crack onset. When strategically placed, a glass-fiber mesh prevented crack propagation.

Analysis of Variance↗
PubMedDate not supplied

In vivo optical coherence tomography of the nasal mucosa.

BACKGROUND: Optical coherence tomography (OCT) is an emerging imaging modality that uses light to produce in vivo high-resolution cross-sectional images (7 microm) of tissues to depths of up to 3 mm. OCT is analogous to ultrasound, but relies on interferometry and low-coherence optical sources to produce images of tissue structure at the histological level. METHODS: In this study, OCT was used to image the mucosa overlying structures in the nasal cavity to obtain information regarding normative in vivo tissue microstructure. An OCT system using a Michaelson interferometer and a 1.3-microm broadband light source was incorporated into a fiber-optic imaging device that was inserted into the nasal cavity. Cross-sectional tomographic images of the anterior and posterior nasal septum, turbinates, and vestibule were acquired in 44 patients in either the office or the operating room during surgical endoscopy. RESULTS: OCT images of the nasal mucosa identified the distinct boundaries between the epithelium, lamina propria, and underlying bone/cartilaginous tissue. Within the lamina propria, features consistent with glands, ducts, and blood vessels were clearly identified. In patients who underwent decongestant therapy, before and after images showed distinct morphological changes in the mucosa. The thickness of the epithelium was tabulated, as well. CONCLUSION: This study establishes the potential of using OCT to produce high-resolution images of the nasal mucosa. As an in vivo tissue microstructural imaging modality, OCT may be valuable in studying the impact of allergic and infectious disease on the nasal mucosa and monitoring its response to pharmacologic therapy.

Adolescent↗
PubMed1990

[Determination of the rate of utilization of glucose in a suspension of erythrocytes].

The authors suggest a new method for measuring the rate of glucose utilization in a cell (red cell) suspension, making use of interferometry. This method allows an easy examination of glucose utilization kinetics in time with but 1000 cells. Thermostatic control of the sample in the cuvette of the device permits detecting the temperature effects on glucose metabolism kinetics and thus define the temperature optimal for the process. A correlation was revealed between the point of structure phase transition in the red cell membrane and the optimal temperature for glucose utilization within the range of physiologic temperatures. This method may be useful in medical, biochemical, physiologic, and hematologic studies. The relative error of the technique is 3 percent.

Blood Glucose↗
PubMed1991

Holographic analysis of the human pelvis.

Twelve fresh human pelves with preserved lumbar spines, hip joints, and ligaments, were tested by double-exposure and sandwich-hologram interferometry. During physiologic loadings (50-300 N), the pelvis moved as a whole downward and backward. Iliac wings exhibited marked undulation, except for the central part, which showed minor deformations. The sacrum moved downward and rotated forward over an axis 5-9 cm below the promontorium. Removal of the sacroiliac interosseous ligaments eliminated all joint movements and caused a tighter contact between articular surfaces. Removal of the sacrotuberous and sacrospinous ligaments had no influence on the pelvic behavior. The magnitudes of deformations as well as their underlying mineral contents were unequally distributed between the two pelvic sides. These results indicate that the sacroiliac interosseous ligaments are the main determinant of sacral movement. Asymmetric load transmittance to the hip joints might be responsible for the mineral content differences between the pelvic sides.

Adult↗
PubMedDate not supplied

Visual acuity testing in cataract--an insight (cataract classification density based).

The senile cataracts have been graded on the basis of density objectively. The letter visual acuity, laser interferometric visual acuity and pin hole visual acuity were compared in various grades of cataracts and controls (phakic and aphakic) in 140 eyes. It was found that good correlation exists in all eyes except when cataract density is grade III or IV. The laser interferometry has good prognostic value when the predictability is assessed in early stages of cataract (Grade I & II).

Cataract↗
PubMed1990

[Holographic deformation analysis of the optic canal in blunt cranial trauma].

The problem in question is the uni- and ipsilateral, acute and irreversible blindness following a minor blunt trauma to the skull without any evidence of a fundus pathology, a fracture in the optic canal or a nerve sheath hematoma. Human cadaver skull bases were examined under static load by means of holographic interferometry. It could be shown that stress lines run in a longitudinal and sagittal direction through the ipsilateral, but transversely through the contralateral optic canal. The complex arrangement of the collagen fibers in the optic nerve sheath and its tough fixation to the bony canal allow only longitudinal-sagittal stress forces to be conducted to the nerve itself, which is consequently stretched and compressed. The transverse direction of the stress lines in the contralateral optic canal, however, are without any mechanical influence on the nerve.

Biomechanical Phenomena↗
PubMed1989

[Retinal function test of eyes with opaque refractive media].

The characteristics of the laser interference fringes of opaque lenses were studied by the laser speckle method. After studies with the opaque lenses in the laboratory, the method was employed in the clinic. The preoperative laser interference fringe visual acuities were compared with the postoperative corrected visual acuities in 65 eyes with mature cataract and 8 eyes with cornea opacities. The authors concluded that the laser speckle interferometry estimated the retinal function of eyes with opaque refractive media quantitatively and it demonstrated practical value in the clinic.

Cataract↗
PubMedDate not supplied

[A polarization-interference method for research on functional stresses in the hard tissues of pathologically worn teeth restored with cast inserts].

The effect of thickness of casted insertion and parapulpar pins (their dimensions and location taken into account) on the strains in the tooth hard tissues was investigated. The holographic interferometry was applied to distinguish between strains in the sections dentin--insertion and dentin--pin. Holograms and focused images were obtained using dual exposition technique. Interference pictures of the bands of absolute step differences were observed on the holograms as a result of light waves diffraction. The technique allowed to perform a combined investigation of strains with due account of capacity in any part of the tooth hard tissue.

Dental Casting Technique↗
PubMed1989

[Laser optic measurements of the axial length of the eye].

A new method has been developed for determining the axial length of the human eye. This method is based on laser interferometry with partially coherent light emitted by a multimode semiconductor laser diode. The measurement procedure is as follows. The subject looks into the laser beam (wavelength approximately equal to 780 nm, power approximately equal to 100 microW), which appears as a red spot. Hence the laser beam acts as a fixation target and measuring beam. This beam passes a Fabry-Perot interferometer in front of the eye. Reflected beams are generated at the cornea and retina. Since the coherence length of the laser used (approximately equal to 25 microns) is less than the difference in path length of the two reflected beams, they will usually not interfere with each other. However, if the distance between the interferometer plates is equal to the optical length of the eye, an interference pattern can be observed. (This is due to a second illuminating beam, which is generated by the interferometer and delayed by two times the interferometer plate distance.) During measurement, the plates are displaced relative to each other until the interference pattern is observed. At this point the plate distance, which can readily be measured, is equal to the optical eye length. This method has several advantages in comparison with the usual ultrasonic technique: it is a non-contact method; no anesthesia is needed; the optical eye length is determined directly; no assumptions need be made about sound velocities in the different eye media. High longitudinal and transversal resolution is achieved (10 microns or better possible). The first measurements obtained with the optical method were compared with the results yielded by the ultrasound technique.(ABSTRACT TRUNCATED AT 250 WORDS)

Eye↗
PubMed1988

[Comparative analysis of the morphochemical changes in the visual and sensorimotor cortical neurons of rats exposed to taftsin].

White rats were treated with a single administration of immunostimulator tuftsin (Thr-Lys-Pro-Arg, in the dose 300 mcg/kg b. w.). By interferometry protein content and concentration and the area of neuron cytoplasm and nucleus were assessed 15 minutes after injection, significant alterations in protein content and cellular area were detected in one type neurons of visual and sensomotor cortex. A possible interrelation is discussed between tuftsin action and the functional activity of neurons, and between the level of their protein metabolism and establishment of emotional and motor response.

Animals↗
PubMed1986

[Optical methods in the study of superficial displacements of the lumbar vertebrae under a vertical load. Initial results and methodological aspects].

In order to assess superficial displacements under load in human lumbar vertebrae, the authors used three different optical methods: photogrammetry under non coherent light; double-exposure holographic interferometry; speckle granularity under laser exposure. Without any structural interposition, the displacements are measured within 10 mu for linear variations and 0.1 degrees for angular variations. Photogrammetry seems to be more adequate for the study of large range of displacements while holographic and speckle techniques are useful to assess, in the displacements, the part of the disc and the osseous structure deformation respectively.

Biomechanical Phenomena↗
PubMed1979

Quantitative tumor cytochemistry--G.H.A. Clowes Memorial Lecture.

Quantitative optical cytochemistry permits the determination of many different parameters in whole cells or parts of cells. Total amounts of DNA, RNA, and protein and/or the amounts of these substances in nucleus or nucleolus are examples. Techniques in this field have contributed considerably to the development of our present conceptions of normal cell growth and regulation. Normal cell study has, however, predominated so that tumor work has not yet been very extensive, even though quite eqrly on, in the 1940's, a conspicuous cytochemical peculiarity was found in cancers, namely, a pronounced variability between cells with regard to several measurable parameters. The result has been different kinds of technical difficulties, which are especially great in work on tumor material. However, as years passed, a fair amount of information was accumulated from studies of different parameters in tumors. Only a few years ago this experience clearly indicated that, provided very considerable improvements were made in technique, several cytochemical methods could be used as efficient supplements to morphological cytodiagnostic work, especially in such important clinical fields as preneoplasia identification, malignancy grading, and judgment of the state of growth of for instance, hormone-stimulated populations and also the distinction, so difficult in morphology, between "atypical hyperplasia" and "truly malignant" states. In an effort to eliminate the foremost of these technical difficulties, during the last few years we have developed a comprehensive system for large-scale uni- and multiparameter measurements aimed specifically at the types of specimens encountered in cytopathological work. The system is based on cytophotometry in ultraviolet and visible light, interferometry, and fluorometry and also encompasses special arrangements to simplify the identification and recovery of individual cells for different types of study. Instruments for facilitation of the comparison of cytochemical results with morphological findings are also included.

Animals↗
PubMedDate not supplied

A remote method for simultaneous measurement of corneal thickness and curvature at a single point.

Advances in refractive surgery have been limited by the measurement technology for determining corneal thickness and curvature. A measurement technique is needed that can provide a detailed corneal thickness and curvature model without contacting the cornea or obstructing the view of the surgeon or surgical equipment. The authors present preliminary results of a method to remotely measure the thickness and curvature of the human cornea at a single point. The method combines ray tracing and interferometry to estimate thickness and curvature in two orthogonal planes in an area less than 100 microns in diameter. This technique has been successfully used to provide very accurate estimates of several thin-shelled test objects. Based upon these results, recommendations are given for further improvement of the technique and extension to a multipoint cornea-modeling system.

Algorithms↗
PubMed1994

Prognostic factors in vitreous surgery for proliferative diabetic retinopathy.

A total of 25 proliferative diabetic eyes of 24 patients scheduled for vitrectomy were examined. The overall preoperative visual acuity was below 0.1, corresponding to hand movement in most patients because of intravitreal hemorrhage. Hence, funduscopy was not possible. The following tests were performed in addition to standard clinical examination: Purkinje entoptic phenomenon, laser interferometry, perception of color flashes, and flicker-VEP using 1.8, 7.6, 15, and 30 Hz as stimulating frequencies. Only the flicker-VEP revealed results predicting reliably the functional visual outcome at 6 months after vitrectomy. Patients with a positive preoperative response to 15 or 30 Hz had a significantly (P < 0.05) better visual outcome at 6 months after vitrectomy (mean postoperative visual acuity 0.11; 95% confidence interval, 1/25-0.32) as compared with patients showing a positive preoperative VEP-response to only 1.8 and 7.6 Hz (mean postoperative visual acuity, hand movement; 95% confidence interval, light without projection--1/35). The flicker-VEP can give additional information about the integrity of the retina and the function of the optic nerve and can therefore help the surgeon to predict the functional result after vitrectomy.

Adult↗