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At least 163 records · Page 9Linked to original sources
PubMed2002

Refractive outcome of cataract surgery using partial coherence interferometry and ultrasound biometry: clinical feasibility study of a commercial prototype II.

PURPOSE: To evaluate the refractive outcome of cataract patients 3 months postoperatively using optical biometry obtained with a prototype version (axial length measurement, ALM, Carl Zeiss Jena) of the commercial partial coherence interferometry (PCI) instrument (IOLMaster, Carl Zeiss Jena). SETTING: Department of Ophthalmology, Vienna General Hospital, and Institute of Medical Physics, University of Vienna, Austria. METHODS: Forty-five patients with age-related cataract in both eyes were scheduled for bilateral cataract surgery. Axial length was measured preoperatively with a prototype (ALM) of the commercial PCI instrument as well as with immersion ultrasound (IUS). Immersion US was performed by a single experienced investigator. In each patient, the first eye was randomly assigned to receive an intraocular lens (IOL) using the Holladay IOL power formula based on ALM or IUS biometry. The other biometric technique was used in the contralateral eye. Subjective refractive outcome was assessed 3 months postoperatively. RESULTS: Refractive outcomes with the 2 techniques did not differ significantly (P = .28). The mean numerical error (MNE) (the difference between the refractive outcome 3 months postoperatively and the predicted spherical equivalent) was 0.13 diopter (D) and 0.03 D for the ALM and IUS, respectively. The mean absolute error (MAE) (the absolute value of MNE) was 0.48 D (range 0.00 to 1.58 D) and 0.46 D (range 0.01 to 1.92 D) with the ALM and IUS, respectively. By recalculating the surgeon factor retrospectively to correct the Holladay formula to obtain a postoperative MNE of zero, a theoretical MAE of 0.46 D was obtained with both biometry techniques. CONCLUSIONS: Refractive outcome in cataract patients using PCI biometry was as good as that achieved with optimized IUS. However, the difference in axial length measured by the ALM compared to that measured by IUS must be considered when using the IOL A-constants supplied by the manufacturers.

Aged↗
PubMed1997

A study of holographic interferometry on the initial reaction of maxillofacial complex during protraction.

Most extraoral appliances used for protracting small or retropositioned maxilla do not allow for variations in the point of force application or in its direction. This variation may be necessary to control vertical, anteroposterior, as well as transverse effects. The purpose of this study was to investigate the initial reaction of the maxillofacial complex according to force magnitude, force direction, and point of force application. For this purpose, an antenna-type modified protraction headgear was tested with double exposure holographic interferometry on a dry human skull with well-aligned upper teeth. Fringe patterns of each protraction condition were compared and analyzed. In most cases, upward rotation of the anterior portion of the maxilla changed to translation, or to downward rotation, as force direction was changed from parallel to the occlusal plane to 20 degrees downward to the occlusal plane. Furthermore, a 500 gm force applied 15 mm above and directed 20 degrees below the occlusal plane produced a translation of the maxillary complex, indicated by a typical circular fringe pattern on the holographic plate, which represents the center of resistance of the maxilla. In most cases, with all force variables tested, a protraction of the maxilla with palatal expansion was more effective in producing translation of the maxilla than was protraction without palatal expansion. By varying force magnitude, force direction and point of force application with maxillary protraction, the amount of maxillary rotation and translation might be controlled.

Adult↗
PubMed2005

Extrinsic Fabry-Perot interferometry for noncontact temperature control of nanoliter-volume enzymatic reactions in glass microchips.

Optical fiber extrinsic Fabry-Perot interferometry (EFPI) was investigated as a noncontact temperature sensor and utilized for regulating the temperature of small-volume solutions in microchips. Interference pattern analysis determined the optical path lengths (OPL) associated with reflections from various surfaces on or in the microchip, in particular, from gold sputtered on the bottom of a microchannel. Since OPL is directly proportional to refractive index, which is dependent on solution temperature, the EFPI sensor was capable of noncontact monitoring of solution temperature simply from alterations in the measured path length. Calibration of the sensor against a thermocouple was performed while heating the microchip in a noncontact manner with an IR lamp. The combination of EFPI temperature sensor, IR-mediated heating, and air cooling allowed a fully noncontact system for small-volume temperature control in microchip structures, and its utility was illustrated by optimal digestion of DNA by a temperature-dependent restriction endonuclease in 320 nL. The functionality and simplicity of the microchip EFPI temperature sensor was enhanced by replacing the prebonding sputtered gold with a tunable, chemically plated semireflective silver coating created in situ after chip fabrication. This provided an 8-fold improvement in the lowest detectable temperature change (deltaT = 0.1 degrees C), facilitated primarily by enhanced reflection from both the bottom and top surfaces of the microchannel. This approach for controlling micro- and nanoscale reactions--with heating, cooling, and temperature control being carried out in a completely noncontact fashion--provides an accurate and sensitive method for executing chemical and biochemical reactions in microchips.

Biosensing Techniques↗
PubMedDate not supplied

Measurement of diffusion coefficients in gels using holographic laser interferometry.

The accuracy and precision of holographic interferometry as a method to measure diffusion coefficients in gels are investigated both experimentally and theoretically. The standard deviations in the experimentally determined diffusion coefficient for ethanol in 4% (w/v) agarose gel were 3.3% for diffusion into the gel and 6.1% for diffusion out of the gel. These are in good agreement with the standard deviations obtained using Monte Carlo simulations. Systematic errors derived from an assumption of constant diffusion coefficients were also investigated.

Computer Simulation↗
PubMed2004

Lysozyme adsorption studies at the silica/water interface using dual polarization interferometry.

Lysozyme adsorption at the silica/water interface has been studied using a new analytical technique called dual polarization interferometry. This laboratory-based technique allows the build up or removal of molecular layers adsorbing or reacting on a lightly doped silicon dioxide (silica) surface to be measured in terms of thickness and refractive index changes with time. Lysozyme adsorption was studied at a range of concentrations from 0.03 to 4.0 g dm(-3) and at both pH 4 and pH 7. Adsorbed layers ranging from 14 to 43 +/- 1 A in thickness and 0.21 to 2.36 +/- 0.05 mg m(-2) in mass coverage were observed at pH 4 with increasing lysozyme concentration, indicating a strong deformation of the monolayer over the low concentration range and the formation of an almost complete sideways-on bilayer toward the high concentration of 4 g dm(-3). At pH 7, the thickness of adsorbed layers varied from 16 to 54 +/- 1 A with significantly higher surface coverage (0.74 to 3.29 +/- 0.05 mg m(-2)), again indicating structural deformation during the initial monolayer formation, followed by a gradual transition to bilayer adsorption over the high concentration end. The pH recycling performed at a fixed lysozyme concentration of 1.0 g dm(-3) indicated a broadly reversible adsorption regardless of whether the pH was cycled from pH 7 to pH 4 and back again or vice versa. These observations are in good agreement with earlier studies undertaken using neutron reflection although the fine details of molecular orientations in the layers differ subtly.

Adsorption↗
PubMed1993

Direct observation of kinesin stepping by optical trapping interferometry.

Do biological motors move with regular steps? To address this question, we constructed instrumentation with the spatial and temporal sensitivity to resolve movement on a molecular scale. We deposited silica beads carrying single molecules of the motor protein kinesin on microtubules using optical tweezers and analysed their motion under controlled loads by interferometry. We find that kinesin moves with 8-nm steps.

Adenosine Triphosphate↗
PubMed2005

Reliability and validity of the partial coherence interferometry for measurement of ocular axial length in children.

PURPOSE: To assess the validity and repeatability of partial coherence interferometry (IOLMaster) and A-scan ultrasound measurement of axial length (AL) in children. METHODS: A prospective comparison of AL measurement made by the IOLMaster optical instrument (Carl Zeiss) and ultrasound A-scan (Alcon) was performed. A total of 20 children (11 male, nine female) were recruited into the study; the mean age of the sample was 11.4 years (range 6.2-15.8). Inclusion criteria comprised individuals <16 years, with no ocular pathology and no previous eye operations or allergy to topical anaesthetics. All measurements were performed by a single examiner. RESULTS: Data on validity show that, on average, a small measurement difference existed between these groups with the IOLMaster being 0.017 mm greater than A-scan ultrasonography. The 95% confidence interval for this difference encompasses zero, demonstrating that no significant systematic bias exists between the two-measurement techniques. Overall, IOLMaster reliability exceeded that of A-scan. This is evidenced primarily by the spread of the paired test-retest difference for A-scan compared to IOLMaster. The mean test-retest difference for A-scan was considerably larger than IOLMaster at 0.042 and 0.004 mm, respectively. CONCLUSION: The results show that IOLMaster was more accurate and reproducible than the contact ultrasonographic technique when used in children. Such results indicate that IOLMaster may be a useful tool in studies of eye growth and refractive development in children.

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↗
PubMedDate not supplied

Characterization of bones by speckle interferometry.

Speckle photography interferometry (SPI) is used to evaluate the stress-strain behaviour of animal bones under loads by recording the speckle fields generated on the bone surface and thus finding the relationship between the fractal dimension D(s) and the compression load P. The procedure consists of application of slow and monotonous compression loads, and recording of the deformation levels and vertical displacements of the specimen. A He-Ne laser beam directed at the surface of bone specimen produces light scattering which generates the speckle. The optical fields show significant differences before and after fracture, due to the changes of the bone surface generated by the strain. Our results support previous suggestions of a relationship between fractal characteristics and parameters related to the mechanical behaviour of materials.

Animals↗
PubMed2000

Characterization of the laryngeal jet using phase Doppler interferometry.

The purpose of this study was to characterize the effects of the laryngeal jet on inhalation air flows in the trachea, and to extend these ideas to further an understanding of aerosol deposition in this region. Phase Doppler Interferometry was used to characterize axial velocity and turbulence intensity contours in the tracheal section of a cadaver-based larynx-trachea model. An array of 30 measurements was made at each of 6 downstream planes within the tracheal portion of the model (immediately downstream of the larynx, and at 0.5, 1, 2, 3, and 4 diameters further downstream). The flow was characterized for steady state flow at three Reynolds numbers (1250, 1700, and 2800). The Re = 1250 case approximates the inhalation of a 6-year-old child. Reverse flows with significant velocities were noted in the anterior trachea within one diameter downstream of the larynx, for all three flow cases. The cross sectional area of the reverse flow regions was larger for the lower Reynolds number cases. These reverse flows are a consequence of the nearly triangular shape of the lumen between the vocal folds in the larynx and constitute a potential deposition mechanism. High levels of axial turbulence intensity were noted near the anterior/left tracheal walls within one diameter downstream of the larynx. This indicates the potential for deposition due to turbulence in this region. Turbulence levels were still significant after four downstream diameters, indicating the potential for turbulent deposition at positions further downstream, including the bronchial tree where passage diameters are smaller. Contrary to expectations, turbulence levels were approximately 20% higher for the Re = 1250 case compared to the Re = 2800 at the furthest downstream locations (with 99% confidence). This is likely due to the complex nature of the confined jet flow.

Aerosols↗
PubMed1999

The mechanical behaviour of human mandibles studied by electronic speckle pattern interferometry.

An understanding of the mechanical behaviour of the human mandible during mastication may be useful in several specific medical fields that examine the maxillofacial area. In this research, the Electronic Speckle Pattern Interferometry Optical Technique was applied to study a dry mandible under external stress. Two images of the mandible, i.e. an image of the relaxed mandible and another of the mandible under stress, were processed using this technique and provided information concerning the most stressed areas of the bone. The advantage of interferometric analysis is that it can be carried out in real time on a mandible to which progressively greater stress has been applied. This research may be of value in maxillofacial surgery, for example, in the diagnosis and treatment of fractured mandibles, and in oral surgery and orthodontics, where it can provide information concerning stress dispersion when an osteointegrated implant or orthodontic appliance is placed in the mouth. One of the most important conclusions to be drawn from the experiments of tension, compression, and in- and out-of-plane deformations is that the capability of the mandible to bend is superior to its capability to stretch. Several quantitative results support this conclusion.

Female↗
PubMed1995

Shearing motion in the hearing organ measured by confocal laser heterodyne interferometry.

To investigate the presence of the postulated shearing motion in the micromechanics of the inner ear during sound stimulations we measured the vibratory response of the tectorial membrane and the reticular lamina in the third cochlear turn in an isolated temporal bone preparation using confocal laser heterodyne interferometry. The mechanical response of the tectorial membrane had the same frequency of maxima as the underlying reticular lamina, but was not as sharply tuned. When the two-dimensional motion was calculated from measurements made from several viewing angles it was found that the vibration of the reticular lamina had significant components both normal and tangential to its surface. The tectorial membrane motion, however, was primarily in a direction approximately perpendicular to the surface of the reticular lamina. The results indicate that shearing motion is produced predominantly by the radial motion of the reticular lamina.

Acoustic Stimulation↗
PubMed2001

Evaluation of eardrum laser doppler interferometry as a diagnostic tool.

OBJECTIVES: Laser Doppler interferometry (LDI) of the eardrum allows noncontact optical analysis of its vibrations in response to sound. Although LDI has been widely used in research, it has not yet been introduced into clinical practice as an adjunctive test for otological workup. The aim of this study was to evaluate LDI as a diagnostic tool in the clinical sphere. STUDY DESIGN: Prospective. METHODS: A measurement system was developed based on a commercially available scanning He-Ne laser Doppler interferometer. The study included 129 eardrums of 79 subjects that were divided into 3 groups: 1) normal subjects and 2) patients with sensorineural and 3) conductive hearing loss (HL). All the patients suffering from conductive HL underwent ossiculoplasty, which allowed confirmation of the final diagnosis, and patients were assigned accordingly to the subgroups malleus fixation, incus luxation, and stapes fixation. RESULTS: The modified LDI system allowed bilateral evaluation of a subject within 30 minutes. No significant difference between normal subjects and patients having sensorineural HL were found. However, it was possible to distinguish between normal subjects and patients with conductive HL. Furthermore, the system had the ability to differentiate between various middle ear diseases. These groups differed statistically significantly in terms of manubrium vibration amplitude and resonance frequency. In malleus fixation significant differences in tympanic membrane movement patterns were found. CONCLUSIONS: Our LDI is applicable in clinical otological practice and serves as a valuable addition to the routine audiological investigations for preoperative evaluation of the mobility and integrity of the ossicular chain.

Adult↗
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↗
PubMed1989

An instrument for in vivo tear film interferometry.

An instrument has been designed and constructed that facilitates the measurement of in vivo tear film topology, thickness, and wetting, using the principles of thin film interferometry. The use of this tear film interferometer (TFI) allows objective evaluation of the breakup characteristics of the tear film on contact lens surfaces and provides a means for examining the dynamic changes in thickness, thickness distribution, and wetting properties during sequential interblink periods. The effects of contact lens material, wetting solutions, and cleaning regimens can be compared objectively. The instrument is easy to use, no additives to the natural tear fluid are required.

Contact Lenses↗
PubMed1993

Measurement of elastic modulus of the bovine cornea by means of holographic interferometry. Part 1. Method and experiment.

Holographic interferometry of the cornea of fresh, enucleated bovine eyes placed in air was used for determination of the elastic modulus of the central part of the cornea. The high sensitivity of the method enables measurement of the radial distension of the cornea even for intraocular pressure (IOP) changes equal to 5 Pa (0.05 mbar or approximately 0.0375 mm Hg). The method of calculation of the tangent Young's modulus of the cornea Et, based on data obtained from double exposure as well as real-time holographic interferograms and on some geometrical data describing the form of the cornea are presented. The average value of Et amounting to 1.42.10(5) Pa was calculated from 2 interferograms of the same eye.

Animals↗