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At least 19 recordsLinked to original sources
PubMed1992

Study of human precorneal tear film thickness and structure using laser interferometry.

The authors previously found that measurements of precorneal tear film thickness in animals, using laser interferometry and confocal microscopy, were larger than earlier estimates. They proposed that this occurred because optical methods did not disturb film structure and measured full thickness, including mucus. In the present study, tear film thickness was measured in humans. Coherent light was reflected from eyes and formed interference patterns. Thickness was determined from spacing of fringes. Mean thickness in six subjects was 34-45 microns, more than four times larger than earlier values. Validity and accuracy of measurements by interferometry were examined in our earlier study using confocal microscopy. Here it provided supportive evidence. Tear film thickness was estimated from optical sections through the corneas of three subjects to be 41-46 microns. Mucus content of the film also was examined. Interferometry was used to measure thinning after application of a mucolytic agent. There was no change in thickness after 5 min exposure to 0.1% (weight/volume) acetylcysteine. Solutions of 20% caused thinning to 11 microns, and thickness slowly increased to reach its original value over 40 min. Thus, the film seemed to be composed substantially of mucus, not aqueous fluid. The results also provided evidence that measurements by interferometry did not include underlying epithelium. Earlier nonoptical methods probably did not include the portion of the film that contained mucus. They seem to have greatly underestimated human tear film thickness.

Adult↗
PubMed1989

Holographic interferometry.

Since its inception three decades ago, holographic interferometry has proven to be a powerful nondestructive testing technique for the measurement of displacement and its derivatives. It is a whole-field, noncontact method which requires the use of a hologram to record three-dimensional information about the surface of an object. After a stress is applied to the object, its new surface geometry is compared with the previously recorded state. Changes of the surface of the object, which are manifest as a series of interference fringes superimposed on the image of the object, can be observed statically or in real time to reveal the displacement. Current state-of-the-art techniques such as heterodyne and digital phase shifting interferometry, which have extended the resolution of holographic interferometry far beyond fringe counting, are reviewed. Particular emphasis is placed upon applications in biomedical engineering and medicine, although potentially applicable techniques from other disciplines are examined. The paper is broken into two main parts. In the first part, the scope and potential limitations of this branch of metrology are presented. In the second part, a review of applications in biomedical engineering is presented. The references cited in the first section are the seminal papers in the field. The applications section, which relies upon the results of the first section, presents a critical review of the literature by analyzing the results of a few representative studies.

Fiber Optic Technology↗
PubMedDate not supplied

[Measurements of the deformation of the femur using speckle interferometry].

A new method for measuring the surface displacement in bones is described. Speckle interferometry was used to study the deformation behaviour of embalmed human femoral bones. The bones were measured under varying loads and conditions. It was shown that the magnitude and direction of displacement could be ascertained at selected points and the strain between any two points could be calculated. The present findings differ from those derived from mathematical models for the femoral bone published so far. The practicability of this technique is outlined. The present results indicate that the technique of speckle interferometry can also be applied to femoral bones with prostheses or external fracture fixations.

Biomechanical Phenomena↗
PubMed1991

Optical measurement of the axial eye length by laser Doppler interferometry.

A new technique has been developed to determine the axial length of the human eye in vivo. Based on laser interferometry in conjunction with the Doppler technique, it uses partially coherent light. This new technique complies with laser safety regulations. High accuracy is achieved, the optical length (OL) can be determined within +/- 30 microns, and the reproducibility of the geometric eye length is greater than +/- 25 microns. Possible errors are discussed. First comparisons with the ultrasound technique yield good agreement for emmetropic subjects and for subjects with a myopia of up to 10 diopters. The advantages of the laser doppler interferometry (LDI) technique are high accuracy, high transversal resolution, and more comfort for the patient (it is a noncontact method; no anesthesia is needed). Possible future applications of LDI, like measurements of fundus profiles and of retinal thickness, are mentioned.

Biometry↗
PubMed1989

[Mechanical evaluation of crown restoration by means of laser holographic interferometry, with a primary regard to establish a system for an experimental method].

This study was conducted to perform mechanical evaluations of crown restorations by Laser Holographic Interferometry (LHI). However, in an application of LHI, the Fujinon Holox FHLX-II system (He-Ne Gas Laser GLG-5700, NEC Co.) to this experiment, it was mandatory to do some modifications for loading and measuring evaluations, thereby a whole sequence of this system could be successfully carried out. The experiments were conducted in the following manner: Ten pieces of full cast crowns were constructed by a conventional procedure with 12% Au-Ag-Pd alloy and each test-piece was cemented alternately by zinc phosphate cement on a master die (stainless steel) with a chamfer margin. Successive vertical loadings (0kg-30kg) were applied for each test-piece and holograms were taken for crown restorations under loadings of both 15Kg & 30Kg with an accuracy of 0.3 micron. Three-dimensional measurements of nine points on surface of a testpiece were obtained through interference fringes, which were converted into mathematical values and statistical comparisons were performed for mean values under loadings of both 15 Kg & 30 Kg. The following results were obtained from this experiment. 1. It was successfully performed that an application of Laser Holographic Interferometry (a real time) became an efficient method with some modifications for mechanical evaluations of crown restorations. 2. Besides modification for rigid fixation of a test-piece, it made possible to conduct the loading experiment under Kg unit, which was impossible in previous studies. 3. Three-dimensional measurements were also made possible by an application of mathematical calculations, thereby a total system of experimental procedures was established. 4. Reference points were marked on surface of a test-piece, and this made possible to compare with the displacement values of other test-pieces. 5. Displacements of experimental crowns with both 15 Kg & 30 Kg under areas of loadings showed remarkably and they were gradually spread out toward the outer directions of restorations with slight displacements. From this experiment, it was proved that a cemented crown showed a certain deformational behavior under loadings. Therefore, this system contributes to become an efficient method evaluating mechanical features of crown restorations for further studies.

Crowns↗
PubMed1989

Use of interferometry in preschool children.

Any procedure that can help to predict the outcome of treatment for a vision disorder is a desired clinical goal. Interferometry has shown such an ability for predicting the post-treatment visual acuities in amblyopia and other vision disorders. In this study, we investigated the effectiveness of using interferometry with preschool children, aged 3-5 years. We determined that they can be reliably tested in 5-10 minutes using a non-verbal, forced choice technique. Due to developmental differences, the 3-year-olds needed slightly more time to test and were more variable in their responses than the 4-years-olds. Overall, the prognostic value of interferometer visual acuity measures should be considered for use in preschool children with visual acuity disorders, e.g., amblyopia.

Amblyopia↗
PubMed1987

Evaluation of double-exposure holographic interferometry for biomechanical measurements in vitro.

Double-exposure holographic interferometry is a nondestructive testing technique for measuring displacement and strain in a test object. A standard hologram contains three-dimensional information about an object. However, the holographic interferogram has additional information, as a series of interference bands overlaid on the three-dimensional image of the object contains information about object deformation. Interferograms were produced for intact cadaveric femora and cadaveric femora with implanted titanium alloy and cobalt-chromium alloy femoral components. A force was applied to the femoral head to simulate single leg stance, and changes in specimen deformation were observed as additional incremental loads were applied. We have observed that the femur behaves as a bending beam and that the holographic technique allows the position of maximal deflection to be identified and the magnitude of femoral displacement from the load axis to be determined at any point within the field of view. The effects of the modulus of the implanted stem on the bending characteristics of the composite structure were clearly seen in the interferograms. This communication presents a photographic analysis of the double exposure interferograms recorded, as well as a critique of the technique for biomechanical measurements in vitro.

Biomechanical Phenomena↗
PubMed1990

Holographic interferometry in the biomechanical study of femoral behavior, with and without prosthesis.

The authors studied the strains acting on a normal femur, and on the same femur fitted with an uncemented screwed prosthesis, by means of the method of holographic interferometry. This modern optical method has the advantage of not requiring any preparation of the surfaces or modification of the bone to be studied. It is non-destructive and can be repeated. This study required 40 interferograms for each case, using two or even three views. Comparison of the images obtained showed major modifications: disappearance of the physiologic flexion of the diaphysis, overload of the upper third, and zones of excess constraint.

Biomechanical Phenomena↗
PubMed1985

Study of the mandible under static constraints by holographic interferometry. New biomechanical deductions.

In order to try to determine the nature of the mechanical structure of the mandible, the authors have compared, with the help of holographic interferometry, the behavior of the fresh mandible of a corpse, of a representative iron angle, and of a block of carbon-carbon under static constraint. There are no similarities between the behavior of the human mandible and that of a polycrystalline steel. On the contrary, the behavior of the mandible and of the carbon-carbon block are very similar. It would be hasty to state that bones are a heterogeneous composite. We can only prove, in a first approach, that they behave similarly under identical experimental conditions. The authors also demonstrated that the mandible presents a "mechanical hysteresis" phenomenon. This means that, when subjected to a small strain, its shape changes, but this change tends to neutralize itself in part in the course of time.

Aged↗
PubMed1987

Holographic interferometry: a critique of the technique and its potential for biomedical measurements.

Double-exposure holographic interferometry is a contactless whole-field method. Dimensional changes are visualized as a series of interference fringes overlaid on the holographic image of the femur, where each fringe represents 0.316 micron (half the wavelength of the laser light) of motion. Interferograms for intact femora and for femora with identical geometry prostheses were produced. We have shown that the femur bends as a beam under axial load. The position of maximum deflection is a function of the properties of the composite structure. Under a known load the amount of deflection can be calculated and the effect of the prosthesis's modulus can be ascertained. In addition to bending, rotational effects can be perceived. Although data interpretation is complex and holographic production is costly and time-consuming, the technique holds promise for biomechanical applications as well as other biomedical disciplines.

Biomechanical Phenomena↗
PubMed1989

Three-dimensional reconstruction of cardiac displacement patterns on the chest wall during the P, QRS and T-segments of the ECG by laser speckle interferometry.

A noninvasive and noncontact technique based on the principle of laser speckle interferometry has been developed to record the cardiac displacements observed on the chest wall. These displacements are then reconstructed in the form of three-dimensional plots, during the P, QRS and T-waves of the ECG. A comparison of these patterns shows that the mechanical activity of each region varies significantly during these phases of cardiac cycle. As these displacements depend on the clinical status of the heart, its use with a cardiac patient shows the functional changes of the affected regions in the form of alteration of these patterns.

Electrocardiography↗
PubMed1992

Flexion characteristics of four-unit fixed partial denture frameworks using holographic interferometry.

Flexion of a metal/ceramic fixed partial denture (FPD) framework under function can cause fracture of the porcelain or deterioration of the cement seal. This study evaluated the flexion under compressive load of a four-unit mandibular FPD replacing the second premolar and the first molar. Testing was accomplished with elapsed time holographic interferometry, using 39 porcelain fused-to-metal frameworks cast with a silver-palladium alloy. The results demonstrated that solder joints at the junction of the premolar and molar pontics flexed under a reduced compressive load and exhibited a higher failure rate than other connector designs.

Analysis of Variance↗
PubMed1985

Efficacy of laser interferometry in predicting visual result of YAG laser posterior capsulotomy.

One hundred fifteen patients with cloudy posterior capsules that required capsulotomies were evaluated by laser interferometry. The predicted acuity was within one line of postoperative acuity in 44 patients (38.3%) and within two lines in 73 patients (63.5%). The correlation coefficient between the predicted and actual post-capsulotomy acuities was 0.38. However, the predicted retinal visual acuity was compared to postoperative Snellen visual acuity and found to differ by an average of three lines. A large number of false negative results reduced the clinical usefulness of the test.

Adolescent↗
PubMedDate not supplied

[Use of holographic interferometry in experimental biomechanics].

Deformation measurements by means of holographic interferometry are of special interest in the fields of osteosynthesis and endoprosthesis research. For osteosynthesis with compression plates holography gives immediately information about the patterns of deformation and thus, the conduction of forces in the system plate-screws fixed to the bone. The mechanical reaction of bone to the design of hip endoprosthesis stems under load can be made visible and in both cases quantitative information is given by calculating the lines of bending.

Biomechanical Phenomena↗
PubMed1992

[Qualitative analysis of the elasticity of the bovine cornea by holographic interferometry].

Double-exposure holographic interferometry is used for deformation analysis of the surface of bovine corneas subjected to intraocular pressure increase. Reproducible individual fringe patterns are recorded for an intraocular pressure of 1340 Pa and subsequent pressure changes of 20, 40 and 80 Pa, respectively. These interference fringes characterize loci of equal displacement. In spite of interindividual variations of the central fringe pattern some basic types can be differentiated: round, oval, drop-like, double-centers, symmetrical as well as unsymmetrical and irregular forms. The peripheral fringe patterns of the cornea can be described by 3 basic types, even taking into account individual variations: circular, circular with an irregular component and irregular. The precision of the method allows to visualize minute local elasticity differences. Results of these investigations do not support the assumption, that the center of the cornea has a higher elasticity than peripheral regions in general. These elasticity differences between central and peripheral areas vary between individual corneas for small intraocular pressure changes at a basic pressure of ca. 10 mm Hg (1340 Pa).

Animals↗
PubMed1988

Elasticity of the bovine sclera measured with real-time holographic interferometry.

Real-time holographic interferometry was used to evaluate the elasticity of the posterior scleral hemisphere of fresh and preserved enucleated bovine eyes. Absolute amplitude values of radial distension were determined for specific locations across the sclera as the tissue was subjected to minute increases in intraocular pressure (IOP). Results indicate that different locations on the globe possess different coefficients of elasticity. Specifically, the supralateral aspect of the posterior globe distended relatively more than the inframedial and medial portions of the globe. Elastic moduli were derived by an areal method in which strain was measured as a change in surface area of the globe, and stress was measured as a change in IOP. Coefficients of elasticity in the range of 3.9 to 9.0 megapascals (MPa) were determined for locations across the posterior scleral hemisphere of the fresh eye used in this study.

Animals↗