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At least 55 records · Page 3Linked to original sources
PubMed2001

Improved prediction of intraocular lens power using partial coherence interferometry.

PURPOSE: To evaluate the feasibility of using a new optical biometry technique, dual-beam partial coherence interferometry (PCI), to improve intraocular lens (IOL) power prediction in cataract surgery. SETTING: Department of Ophthalmology, Vienna General Hospital, and Institute of Medical Physics, University of Vienna, Vienna, Austria. METHODS: Preoperative axial length (AL) data obtained with PCI biometry and applanation ultrasound (US) biometry in 77 eyes of 51 patients was applied to 4 commonly used IOL power formulas. The refractive outcome and the mean absolute error (MAE) were calculated for each formula using both biometry methods. A linear multiple-regression model based on preoperative PCI biometry data was derived to predict the postoperative anterior chamber depth (ACD). The predictive power of this regression model was assessed by adding the predicted ACD to the SRK/T formula. Predicted residuals were calculated to evaluate the feasibility and stability of this modified IOL power formula. RESULTS: Using PCI instead of US biometry significantly improved the refractive outcome with all 4 IOL power formulas. The Holladay I and SRK/T formulas yielded an MAE of 0.44 diopter (D) using PCI AL data and 0.56 D and 0.57 D, respectively, using US biometry data. The SRK/T formula combined with the PCI regression model for postoperative ACD prediction performed slightly better (MAE 0.42 D) than the conventional SRK/T formula alone. Predicted residuals revealed an MAE of 0.46 D, proving the predictive performance of the new formula. CONCLUSIONS: Partial coherence interferometry biometry applied to several widely used IOL power formulas yielded significantly better IOL power prediction and therefore refractive outcome in cataract surgery than US biometry. Further improvement can be achieved by applying PCI to a modified SRK/T formula that predicts the postoperative ACD using PCI biometry data.

Biometry↗
PubMed2002

Accuracy and reproducibility of biometry using partial coherence interferometry.

PURPOSE: To determine whether partial coherence interferometry is comparable to standard contact ultrasonic biometry in accuracy, reproducibility, and ease of use. SETTING: Academic university practice. METHODS: In this prospective study, simultaneous biometry was performed in 91 consecutive patients (111 eyes) using partial coherence interferometry (IOLMaster, Zeiss Humphrey Systems) and ultrasonic biometry (I(3), Innovative Imaging, Inc.). The differences between the predicted spherical equivalent in diopters (D) and the actual results with both techniques were compared. RESULTS: The IOLMaster was significantly better in the mean absolute error (0.533 D +/- 0.589 [SD] versus 0.757 +/- 0.723 D; P = .012) and the percentage of eyes within +/-0.5 D (61.2% versus 42.3%; P = .003) and +/-1.0 D (87.4% versus 77.5%; P =.05) of the predicted refraction. CONCLUSION: The IOLMaster was more accurate and reproducible than the contact ultrasonographic technique.

Biometry↗
PubMed2002

Immersion A-scan compared with partial coherence interferometry: outcomes analysis.

PURPOSE: To compare 2 methods of axial length measurement, immersion ultrasonography and partial coherence interferometry, and to elucidate surgical outcomes based on immersion measurements. SETTING: Oregon Eye Institute, Eugene, Oregon, USA. METHODS: Axial length measurements in 50 cataractous eyes were obtained by optical biometry (IOLMaster, Zeiss Humphrey Systems) and immersion ultrasound (Axis II, Quantel Medical), and the results were compared. Intraocular lens (IOL) power calculations in the same eyes after cataract extraction and posterior chamber IOL implantation were evaluated retrospectively based on the postoperative spherical equivalent prediction error. RESULTS: Immersion ultrasonography and partial coherence interferometry measurements correlated in a highly positive manner (correlation coefficient = 0.996). Outcomes analysis demonstrated 92.0% of eyes were within +/-0.5 diopter of emmetropia based on immersion axial length measurements. CONCLUSION: Immersion ultrasonography provided highly accurate axial length measurements and permitted highly accurate IOL power calculations.

Biometry↗
PubMed2002

Biometry of cataractous eyes using partial coherence interferometry: clinical feasibility study of a commercial prototype I.

PURPOSE: To evaluate the clinical feasibility of the prototype version of a commercial partial coherence interferometry instrument (axial length measurement, ALM, Carl Zeiss Jena) for noninvasive, high-precision biometry in cataractous eyes. SETTING: Department of Ophthalmology, Vienna General Hospital, and Institute of Medical Physics, University of Vienna, Austria. METHODS: The preoperative axial length in 49 eyes of 37 cataract patients was measured with the commercial (ALM) and laboratory (PCI) prototypes of the partial coherence interferometry instrument, as well as with immersion ultrasound (IUS). RESULTS: Axial length measurements with the ALM and PCI did not differ significantly (P = .23). Both prototypes assessed longer axial lengths than the IUS technique (P < .0001; median 203 microm; range -476 to +635 microm). The precision of the axial length measurement was 18 microm, 28 microm, and 54 microm with the PCI, ALM, and IUS, respectively. CONCLUSIONS: Partial coherence tomography is a high-precision, high-resolution, noncontact biometric technique.The commercial PCI prototype is practical in clinical use, with improved comfort for patients, no need for anesthesia, and a reduced risk of infection. However, the difference between the PCI and IUS in axial length measurement must be considered when using the constants supplied by intraocular lens (IOL) manufacturers for IOL power calculations.

Adult↗
PubMed2002

Comparison of ultrasound pachymetry and partial coherence interferometry in the measurement of central corneal thickness.

PURPOSE: To compare central corneal thickness (CCT) measurements obtained with 3 ultrasound pachymeters and with partial coherence interferometry (PCI) and evaluate the effect of repeated contact by a pachymetry probe on corneal thickness. SETTING: Department of Ophthalmology, University of Vienna, Vienna, Austria. METHODS: Central corneal thickness was measured in 20 eyes of 20 healthy volunteers with 3 different ultrasound pachymeters (DGH 500, DGH Technology Inc.; SP 2000, Tomey Inc.; Paxis, Biovision Inc.) and with PCI. In each eye, 5 measurements with PCI were followed by 5 measurements with each ultrasound pachymetry device and another 5 measurements with PCI. RESULTS: The mean CCT measured with the DGH 500, SP 2000, and Paxis was 541.0 microm, 539.2 microm, and 545.1 microm, respectively. Although the differences among the 3 ultrasound pachymetry devices were within 6.0 microm, they were statistically significant (P<.05). The PCI measurements were significantly smaller (P <.05) than the ultrasound measurements: 518.8 microm before and 517.5 microm after repeated contact with the ultrasound pachymetry probe (P <.05). The mean precision (standard deviation) was 0.77 microm for PCI and between 2.40 microm and 3.58 microm for ultrasound pachymetry measurements. The correlation coefficients for the intraobserver variability were 0.999 for PCI and between 0.987 and 0.995 for ultrasound pachymetry measurements. CONCLUSIONS: Partial coherence interferometry was the more precise method of measuring CCT and had better intraobserver variability. Repeated contact by a pachymetry probe reduced corneal thickness by 1.3 microm. However, the reason for the smaller measurements with PCI than with ultrasound pachymetry remains unclear.

Adult↗
PubMed1994

Holographic interferometry of intact and radially incised human eye-bank corneas.

Many methods to measure corneal elasticity destroy the tissue and thereby produce erroneous results. Holographic interferometry, a highly precise nondestructive optical comparison technique, was used to evaluate corneal elasticity of intact eye-bank eyes. A double-pulse holographic interferometer operating at 632.8 nm was used to measure corneal deformation in 20 whole-globe eyes from donors 45 to 83 years of age for intraocular pressures from 16 mm Hg to 21 mm Hg. Stress was computed from LaPlace's law, and arc length strain was derived from z-axis distention of the central cornea. The stress-strain relationship in the normal physiological range of intraocular pressure was linear with a Young's elastic modulus of 1.03 gigapascals for the central cornea (r = 0.999). During interferometry of radial keratotomy of the cornea, interference fringe patterns developed in association with each incision as it was made. When four incisions were placed deep along each of the primary semimeridians, the fringe pattern developed as expected, based on current keratotomy models. When incisions were shallow (approximately 50% depth) and placed asymmetrically along the nasal, temporal, and superior semimeridians, the resulting surface strain was symmetrical about the central cornea, forming an annular pattern of interference fringes. These results indicate that when the cornea was stressed at physiological pressures as part of the intact whole globe, it was less elastic than excised corneal tissue tested by strip extensiometry. Radially incised corneas demonstrated strain patterns suggestive of inherent structural anisotropy with a possible inferior quadrant weakness.

Adult↗
PubMed1998

High precision biometry of pseudophakic eyes using partial coherence interferometry.

PURPOSE: To investigate the applicability of the scanning version of dual-beam partial coherence interferometry (PCI) for measuring the anterior segment and axial length of pseudophakic eyes in a clinical setting and to determine the achievable precision with this biometry technique. SETTING: Department of Ophthalmology, Vienna General Hospital, and Institute of Medical Physics, University of Vienna, Austria. METHODS: Partial coherence interferometry was performed in 39 pseudophakic eyes of 39 patients after implantation of a foldable acrylic intraocular lens (IOL). RESULTS: Effective lens position (ELP), IOL thickness and lens-capsule distance (LCD) were determined with a precision of 2 to 3 microns; corneal thickness and axial eye length, with a precision of 0.8 and 5.0 microns, respectively. The mean ELP of the IOL was 4.093 mm +/- 0.290 (SD). In 7 eyes (18%), a positive LCD of 68 +/- 40 microns was detected with PCI. Mean corneal thickness was 526.4 +/- 31.5 microns; mean IOL thickness, 791.5 +/- 40.2 microns; and mean axial length, 23.388 +/- 0.824 mm. CONCLUSION: The scanning version of PCI enables high precision (< or = 5 microns) and high resolution (approximately 12 microns) biometry of pseudophakic eyes that is better than conventional ultrasound by a factor of more than 20. For the first time, positive LCD, a possible risk factor for posterior capsule opacification, could be detected and quantified. Furthermore, this technique offers a high degree of comfort for the patient since it is a noncontact method with no need for local anesthesia or pupil dilation and has a reduced risk of corneal infection.

Acrylates↗
PubMed2000

Mechanical properties of bovine aortic endothelial cells in suspension studied by ultrasonic interferometry.

OBJECTIVE: Cell adhesion phenomenon has been extensively studied in the last decade and was shown to be mediated by specialized molecules and driven by physical forces. Cohesion of the vessel wall cells is also dependent on adhesion molecules but less is known about the physical forces involved. To investigate endothelial cell/endothelial cell interaction from a mechanical point of view, we have used an ultrasonic interferometry device, named EchoCell, which has been previously designed to study red blood cell-red bood cell (RBC-RBC) interaction. METHODS: Bovine aortic endothelial (BAE) cells were cultured, detached, then suspended in buffer and their mechanical and geometrical properties studied with the EchoCell system. The ultrasonic apparatus measures both the accumulation rate of cells in suspension on a solid plate and the acoustical impedances of the suspension and the sediment. RESULTS: In suspension, BAE exhibited, in our experimental conditions (3x10(6) cells per ml), a spherical size evaluated by calculation at a mean radius of 7+/-2 microm. Moreover, no BAE aggregation occurred at the concentrations used. The acoustical impedance of the BAE suspensions calculated from all the samples studied, in the cell concentration range from 1.5x10(6) to 6x10(6) cells per ml, was 1.52x10(6) Rayl (kg m(-2) s(-1)). Furthermore, the acoustical impedance of the cell sediment was found to be independent on the initial cell suspension concentration and equal to 1.63x10(6) Rayl (kg m(-2) s(-1)). Estimation of the volume fraction of BAE inside the sediment allows to evaluate the ultrasonic velocity and the elastic bulk modulus of cells. CONCLUSION: The ultrasonic interferometry method appears particularly interesting to study geometrical and mechanical (acoustical impedance, sound velocity, elastic bulk modulus) properties of BAE cells.

Animals↗
PubMed1994

[Measurement of immunologic agglutination of erythrocytes by ultrasonic interferometry].

Ultrasound interferometry is a new methodology which has been developed in our laboratories in order to measure precisely and quickly the size of particles sedimenting in liquid on horizontal surface, upon gravity. Applied to red blood cells, this method evaluates the sedimentation of erythrocytes, their aggregation induced by proteins or aggregating compounds as well as their agglutination upon immune reactions. The quantitative assessment of red cell agglutination was applied to the study of blood groups and to the search for red cell antibodies. Preliminary results show that ultrasound interferometry is 1) quantitative, measuring the size of agglutinates; 2) sensitive; 3) specific; 4) fast; 5) able to detect irregular antibodies.

Erythrocytes↗
PubMed2000

A chip-scale universal detector for electrophoresis based on backscattering interferometry.

An on-chip detector based on backscatter interferometry has been developed to perform sub-nanoliter volume refractive index measurements. The detection system consists of a simple, folded optical train based on the interaction of a laser beam and an etched channel in a silica (glass) plate. This etched channel is composed of two radii joined by a flat portion which define a curved surface in the shape of a half cylinder in a silica (glass) plate. The backscattered light from the channel takes on the form of a high contrast interference pattern that contains information related to the bulk properties of the fluid located within the probe volume. Positional changes of the interference pattern extrema (fringes) allow for the determination of refractive index changes at the 10(-6) level in a detection volume of 188 x 10(-12) L. Under capillary electrophoresis (CE) conditions, the injected mass detection limits for small molecules with little native absorption ranges from 530 fmol (0.18 ng) for sucrose to 720 fmol (0.43 nanograms) for raffinose. Fluorescein was also used to evaluate the technique for universal CE and under further optimized conditions can be quantified at the 150 microM level. Separation performance for the solutes tested ranged from about 2300 to 15,500 plates or 61,000 to 400,000 N m-1. The results presented here indicate there is potential for using the simple optical train of backscattering interferometry for on-chip universal solute analysis.

Electrophoresis, Capillary↗
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↗
PubMed2002

Vibration measurement of the tympanic membrane of guinea pig temporal bones using time-averaged speckle pattern interferometry.

"Time-averaged holography" and "holographic interferometry" enable recording of the complete vibration pattern of a surface within several seconds. The results appear in the form of fringes. Vibration amplitudes smaller than 100 nm are not readily measurable by these techniques, because such small amplitudes produce variations in gray level, but not fringes. In practice, to obtain clear fringes in these measurements, stimulus sound pressures higher than 100 dB SPL must be used. The phase of motion is also not obtainable from such fringe techniques. In this study, a sinusoidal phase modulation technique is described, which allows detection of both small amplitudes of motion and their phase from time-averaged speckle pattern interferometry. In this technique, the laser injection current is modulated and digital image processing is used to analyze the measured patterns. When the sound-pressure level of stimuli is between 70 and 85 dB SPL, this system is applied to measure the vibratory response of the tympanic membrane (TM) of guinea pig temporal bones at frequencies up to 4 kHz where complicated vibration modes are observed. The effect of the bulla on TM displacements is also quantified. Results indicate that this system is capable of measuring the nanometer displacements of the TM, produced by stimuli of 70 dB SPL.

Animals↗
PubMed2002

Utilization of moiré interferometry to study the strain distribution within multi-layer thermoplastic elastomers.

The use of soft elastomeric cushion form bearings as an alternative material to ultra-high molecular weight polyethylene (UHMWPE) has been proposed in the literature as providing enhanced lubrication and lower friction. However, the abrupt change in stiffness between the bearing's soft contact layer and its rigid support substrate results in high shear stresses and leads to the debonding of the soft layer from the substrate. The use of functionally modulus-graded material has been proposed as a solution to this problem. This paper investigates the use of moiré interferometry to study the strain distribution within and across the interfaces of multi-layer elastomeric samples, which were fabricated as models for functionally modulus-graded materials. While this technique has been widely used to study the strain distribution in rigid materials and composites, this paper represents the first report of its application to low-modulus polymers at temperatures where they exhibit significant viscoelastic behavior. The results presented clearly demonstrate that the moiré interferometry technique can be successfully applied in the field of low-modulus elastomeric materials. The analysis of the moiré patterns suggests that the soft elastomeric material under the contact point was subjected to a compressive epsilonx, and was pushed sideways. The analysis also showed that the maximum shear strain occurred where the deformation was constrained, which could possibly lead to a local fatigue failure in the sample.

Biomedical Engineering↗
PubMed1997

Determination of the foveal cone spacing by ocular speckle interferometry: limiting factors and acuity predictions.

We have developed a high-resolution imaging technique, based on speckle interferometry, for the objective determination of the cone spacing in the living human fovea. The spatial resolution attained with this technique is theoretically diffraction limited by the pupil size. However, the highest frequency that we measure varies greatly among subjects, especially for fully dilated pupils. We have conducted several experiments (determination of the cutoff frequency of ocular speckle interferometry, the double-pass modulation transfer function, and the Stiles-Crawford effect) that indicate that, as expected, the resolution is not limited by the incoherent modulation transfer function. We found, though, a high correlation between the cutoff frequency and the width of the eye's Stiles-Crawford function. This implies that the resolution depends on the structural properties of the cone mosaic itself. In addition, we have compared the Nyquist frequency of the cone mosaic, determined objectively by our technique, with the grating visual acuity measured in the same eyes at the same foveal eccentricities. For our subjects, visual resolution nearly matches the Nyquist frequency within the fovea, except at the foveal center, where the optical transfer function of the eye attenuates the contrast of frequencies close to the Nyquist limit to a value below threshold.

Cell Count↗
PubMed1999

Spectrally resolved white-light interferometry for measurement of ocular dispersion.

Spectrally resolved white-light interferometry was used to measure the wavelength dependence of refractive index (i.e., dispersion) for various ocular components. Verification of the technique's efficacy was substantiated by accurate measurement of the dispersive properties of water and fused silica, which have both been well-characterized in the past by single-wavelength measurement of the refractive index. The dispersion of bovine and rabbit aqueous and vitreous humors was measured from 400 to 1100 nm. In addition, the dispersion was measured from 400 to 700 nm for aqueous and vitreous humors extracted from goat and rhesus monkey eyes. An unsuccessful attempt was also made to use the technique for dispersion measurement of bovine cornea and lens. The principles of white-light interferometry, including image analysis, measurement accuracy, and limitations of the technique, are discussed. In addition, alternate techniques and previous measurements of ocular dispersion are reviewed.

Animals↗
PubMed2003

Delay and dispersion characteristics of a frequency-domain optical delay line for scanning interferometry.

The reflective frequency-domain optical delay line employing a diffraction grating, a lens, and a tiltable mirror has emerged as a device particularly suitable for interferometry and optical coherence tomography. The device is comprehensively described, both theoretically and experimentally, in the context of interferometry. The variations of phase and group delay produced by the device as well as its dispersive properties are described and demonstrated experimentally.

Interferometry↗
PubMed2003

Time-domain interferometry for direct electric-field reconstruction by use of an acousto-optic programmable filter and a two-photon detector.

We introduce a new approach to the characterization of femtosecond optical pulses based on a remarkably simple setup combining a two-photon detector and a pulse shaper consisting of a longitudinal acousto-optic programmable filter. The operation of this setup is demonstrated through the use of a new version of spectral phase interferometry for direct electric-field reconstruction based on time-domain instead of on frequency-domain interferometry.

Acoustics↗
PubMed2003

Measurement of dye diffusion in agar gel by use of low-coherence interferometry.

We demonstrate low-coherence interferometry for diffusion measurements. We have measured the diffusion coefficient of a phthalocyanine dye in 1.5% agar gel with a two-wavelength interferometer; one wavelength was matched to the absorption peak of the dye at 675 nm, while the other, 805 nm, was not affected by the dye. The diffusion coefficient of the dye was found by fitting a mathematical model for the interferometer signal to the measured low-coherence interferometry amplitude. A 95% confidence interval for the diffusion coefficient was found to be D = (2.5 +/- 0.2) x 10(-10) m2/s. The influence of speckle averaging and experiment time on the determination of the diffusion coefficient has been studied. The presented technique allows in situ characterization of diffusion in semitransparent media.

Agar↗