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PubMed1997

Biometric investigation of changes in the anterior eye segment during accommodation.

Non-invasive biometry of the anterior structures of the human eye can be performed with unprecedented precision of 8-10 microns and a resolution of approximately 9 microns by partial coherence interferometry, which has the potential to assess the effect of cycloplegia on the ocular components of the anterior eye segment, to further improve the precision to 1-2 microns by the use of these agents and to quantify the amount of residual accommodations in different states of cycloplegia. In addition, the anterior chamber depth, the thickness of the crystalline lens, their changes during accommodation, as well as the movement of the anterior and posterior lens pole during accommodation can be quantified objectively and accurately to investigate the mechanism of accommodation.

Accommodation, Ocular↗
PubMed1997

Optical coherence tomography of the human skin.

BACKGROUND: Optical coherence tomography (OCT) is a new diagnostic method for tissue characterization. OBJECTIVE: We investigated normal and pathologic structures in human skin in several locations to evaluate the potential application of this technique to dermatology. METHODS: Based on the principle of low-coherence interferometry, cross-sectional images of the human skin can be obtained in vivo with a high spatial resolution of about 15 microns. Within a penetration depth of 0.5 to 1.5 mm, structures of the stratum corneum, the living epidermis, and the papillary dermis can be distinguished. RESULTS: Different layers could be detected that were differentiated by induction of experimental blisters and by comparison with corresponding histologic sections. Furthermore, OCT images of several skin diseases and tumors were obtained. CONCLUSION: OCT is a promising new imaging method for visualization of morphologic changes of superficial layers of the human skin. It may be useful for noninvasive diagnosis of bullous skin diseases, skin tumors, and in vivo investigation of pharmacologic effects.

Adult↗
PubMed1997

Tympanic membrane changes in experimental purulent otitis media.

The stiffness properties of the gerbil tympanic membrane (TM) were investigated during the early course of experimental purulent otitis media produced by middle ear inoculation (n = 49) with type 3 Streptococcus pneumoniae. In a first approach the acoustic admittance and susceptance were measured in vitro with tympanometry and in a second approach the tympanic membrane displacement in response to static pressure was measured with moire interferometry. A histological assessment of the tympanic membrane was made concurrently. The acoustic admittance and susceptance reduced during the initial days post-inoculation. These reductions seem to correlate with an oedema simultaneously developing in the pars tensa. The pressure-induced displacement increased with time of disease, i.e. the mechanical stiffness of the TM reduced. Local deformation zones, or 'weak spots' appeared in the inferior half of the pars tensa in three out of eight cases measured at 3 or 4 days post-inoculation. The loss of stiffness in the pars tensa may affect the further course of otitis media, and the 'weak spots' are possible precursors of retraction pockets and/or perforations. The stiffness reductions may be caused by changes on a sub-microscopical, molecular level.

Acoustic Impedance Tests↗
PubMed1999

Micromechanical effects in the cochlea of tetracaine.

Local anesthetics applied in the tympanic cavity have earlier been shown to affect the gross receptor potentials in reducing the cochlear microphonics and increasing the positive summating potential. To study the effects of this drug on the mechanical responses in the cochlea, vibrations were measured using laser heterodyne interferometry in an isolated in vitro temporal bone preparation from the guinea pig. Measurements were made at a set of frequencies in the fourth cochlear turn from the Hensen's cells and the outer hair cells in response to sound applied to the ear. The tuning curves of the fundamental and the second harmonic components of the vibratory responses were plotted. When 2 mM tetracaine was applied, the high frequency slope of the second harmonic curve shifted down in frequency, this caused the frequency of the maximum of second harmonic tuning to shift down. These changes were reversible when tetracaine was washed out. Observations were also made in the temporal bone preparation in vitro with a confocal microscope. Fluorescent probes were used to label various structures in the organ of Corti. Optical sections were obtained by tilting the organ permitting a view from the side like a radial section through the organ. Images were acquired before, during and after application of tetracaine and were later analyzed with a computer program. Simultaneously, cochlear microphonics and the summating potential were obtained to monitor the electrical response of the preparation. Although the cochlear microphonics and summating potential decreased when 2 mM tetracaine was applied, structural changes were not measurable in the organ of Corti. The decrease was reversible when tetracaine was washed out. It is concluded that tetracaine affected the high frequency part of the non-linear second harmonic component, possibly by lowering the stiffness of the stereocilia bundle or the body of the outer hair cells.

Acoustic Stimulation↗
PubMed2003

Optical and ultrasound measurement of axial length and anterior chamber depth for intraocular lens power calculation.

PURPOSE: To evaluate the precision, reproducibility, and applicability of an optical method based on partial coherence interferometry for intraocular lens (IOL) power calculation. SETTING: Ultrasound laboratory of a university eye hospital. METHODS: A prospective comparison of measurements made by the IOLMaster optical instrument (Carl Zeiss) and Ultrascan Digital 2000 contact ultrasound A-scan (Alcon) for IOL calculations was performed. Examined were 255 eyes of 134 persons (204 phakic, 47 pseudophakic, and 4 aphakic). The mean age of the patients was 67.9 years (range 7 to 94 years). RESULTS: The IOLMaster measurements were successful in more than 80% of cases: in 82%, 99%, and 99% for axial length (AL), anterior chamber depth (ACD), and keratometry measurements, respectively. The reproducibility of the AL and ACD measurements was very high (coefficient of variation 0.13% and 2.20%, respectively). The AL and ACD values were significantly larger with the IOLMaster (P <.001) than with the Ultrascan Digital 2000. The correlation between ultrasound and optical AL measurements was high (r = 0.985; P <.001); however, there was no correlation between ACD measurements (r = 0.079; P =.397). The corneal refractive power measurements of a Javal-type keratometer and the IOLMaster were highly correlated (r = 0.955; P <.001), with a mean difference of 0.2 diopter. CONCLUSIONS: The results show that measurements for IOL calculation are easy and precise with the optical method. It is a noncontact method, so no anesthesia is needed and there is no risk of infection.

Adolescent↗
PubMed2003

Intraocular lens movement caused by ciliary muscle contraction.

PURPOSE: To investigate intraocular lens (IOL) movement, measured as a change in anterior chamber depth (ACD) caused by pilocarpine-induced ciliary muscle contraction. SETTING: Department of Ophthalmology, University of Vienna, Vienna, Austria. METHODS: In this prospective study, the ACD was measured using high-precision, high-resolution, dual-beam partial coherence interferometry in 62 pseudophakic eyes of 55 patients under pilocarpine- and cyclopentolate-induced ciliary muscle contraction and relaxation. The following were studied: 2 models of a ring-haptic IOL (designed to accommodate), a plate-haptic IOL, and 3 types of 3-piece IOLs. Measurements were performed 3 months after surgery. RESULTS: The ring-haptic IOLs and plate-haptic IOL showed a forward movement (ring haptic 43A, -116 microm; ring haptic 43E, -222 microm; plate haptic -162 microm). The 3-piece IOLs showed no change in ACD except in 1 IOL type in which there was backward movement (156 microm). CONCLUSIONS: Pilocarpine-induced ciliary muscle contraction caused forward movement of ring- and plate-haptic IOLs that resulted in an estimated accommodative amplitude of less than 0.50 diopter in most cases. The accommodating ring-haptic IOLs did not perform better than the conventional plate-haptic IOL.

Accommodation, Ocular↗
PubMed2003

Comparison of anterior chamber depth measurement methods in phakic and pseudophakic eyes.

PURPOSE: To compare anterior chamber depth (ACD) measurements in phakic and pseudophakic eyes using a slit-beam photographic technique (IOLMaster, Carl Zeiss Meditec AG) with those obtained with the laboratory prototype version of partial coherence interferometry (PCI) and with conventional applanation ultrasound in phakic eyes. SETTING: Department of Ophthalmology, Vienna General Hospital, Vienna University, Vienna, Austria. METHODS: Thirty-three ACDs of 28 patients with age-related cataract were measured preoperatively with a slit-beam photographic technique (IOLMaster) and the prototype version of PCI. In 24 eyes, the ACD was also assessed with applanation ultrasound. In addition, 34 ACDs of 18 pseudophakic patients in a different study population were examined postoperatively with the IOLMaster and PCI. RESULTS: The median ACD in the phakic eyes was 3.06 mm (range 1.93 to 3.90 mm) with the IOLMaster, 3.09 mm with PCI (range 1.49 to 4.06 mm), and 2.87 mm (range 2.18 to 3.33 mm) with applanation ultrasound. The precision was 0.005 mm for PCI and 0.015 mm for IOLMaster measurement. The median difference between the IOLMaster and PCI ACD biometry was 0.01 mm +/- 0.14 (SD) (range -0.44 to 0.17 mm) (P =.71). In pseudophakic eyes, the 2 methods showed a median difference of -0.22 mm (range -0.45 to 1.99 mm) (P >.1) and did not correlate (r = 0.21; P >.2). CONCLUSIONS: In phakic eyes, the difference between IOLMaster and PCI measurements was small and not statistically significant. In pseudophakic eyes, the difference was larger and the methods did not correlate.

Anterior Chamber↗
PubMed2003

Postoperative change in effective lens position of a 3-piece acrylic intraocular lens.

PURPOSE: To study the change in postoperative position of an angulated, 3-piece, foldable acrylic intraocular lenses (IOLs) and evaluate the effect of a sharp posterior optic edge compared with that of a round optic edge on the change in postoperative anterior chamber depth (ACD). SETTING: Department of Ophthalmology, University of Vienna, Vienna, Austria. METHODS: This randomized intraindividual-comparison study comprised 104 eyes of 52 patients with age-related cataract. Patient received a sharp-edged Sensar OptiEdge AR40e IOL (Allergan Surgical) in 1 eye and a round-edged Sensar AR40 IOL in the other eye. Postoperative follow-up included ACD measurement by partial coherence interferometry and evaluation of the capsulorhexis area by standardized retroillumination photography at 1 day, 1 week, and 1 and 6 months. RESULTS: A decrease in ACD during the first postoperative week was followed by a small increase in ACD during the first 6 months. There was no significant difference between the sharp-edged group and the round-edged group. CONCLUSIONS: The angulated 3-piece acrylic IOLs showed significant forward movement over the first postoperative 6 months. Although the change in refraction was small, there was variability among patients. The sharp posterior optic edge design did not affect the IOL's movement in the capsular bag.

Acrylic Resins↗
PubMed1998

Accurate determination of effective lens position and lens-capsule distance with 4 intraocular lenses.

PURPOSE: To measure effective lens position (ELP) of 4 intraocular lenses (IOLs) using high precision and high resolution dual-beam partial coherence interferometry (PCI) and to assess the tendency of these IOLs to produce a lens-capsule distance (LCD), a possible risk factor for posterior capsule opacification. SETTING: Department of Ophthalmology, Vienna General Hospital; Institute of Medical Physics, University of Vienna, Austria. METHODS: In a retrospective study, PCI was used to measure ELP and LCD in 139 pseudophakic eyes of 110 patients with 4 IOLs: acrylic 3-piece IOL (AcrySof MA60BM); silicone 3-piece IOL without a capsular tension ring (PhacoFlex SI30) and with a capsular tension ring (PhacoFlex SI30 and Morcher Type 14); silicone plate-haptic IOL (Staar AA4203VF); and a hydrogel plate-haptic IOL (logel 1103). RESULTS: The ELP and LCD were determined with a precision of approximately 3 to 4 microns. An LCD was detected in 21% eyes with the AcrySof, 20% of eyes with the SI30 without a capsular tension ring, 10% of eyes with a capsular tension ring, 21% of eyes with the Staar, and 17% of eyes with the logel. The LCDs detected by PCI, but not by slitlamp examination, were significantly smaller than those detected by both. CONCLUSION: The amount of LCD detected by PCI was approximately the same with all IOL types (approximately 20%) except the PhacoFlex SI30 with a capsular tension ring (10%).

Acrylates↗
PubMed1999

Changes in intraocular lens position after neodymium: YAG capsulotomy.

PURPOSE: To quantify changes in intraocular lens (IOL) position caused by neodymium: YAG (Nd:YAG) capsulotomy with 3 IOL styles. SETTING: Department of Ophthalmology, University of Vienna, Austria. METHODS: In a prospective study, anterior chamber depth (ACD) was measured by dualbeam partial coherence interferometry (PCI) in 32 pseudophakic eyes of 32 patients with posterior capsule opacification before and immediately after planned capsulotomy under mydriasis. Patients were divided into 3 groups with the following IOL styles: 1-piece poly(methyl methacrylate) (PMMA), 3-piece foldable, and plate haptic. RESULTS: The capsulotomy induced a backward IOL movement in all 32 eyes (mean 25 microns; range 9 to 55 microns). It was more pronounced in eyes with plate-haptic IOLs than in those with the other styles. Precision of ACD measurement by PCI was 4 microns. Changes in ACD correlated significantly with capsulotomy size but not with preoperative lens-capsule distance. CONCLUSION: Capsulotomy caused a backward movement of the IOL, which was more pronounced with plate-haptic IOLs than with 1-piece PMMA and 3-piece foldable IOLs. Since the magnitude of IOL movement in this study population was small, a hyperopic shift in refraction after capsulotomy will usually be small and not clinically relevant.

Adult↗
PubMed2001

Analysis of the response of planar polarization interferometer to molecular layer formation: fibrinogen adsorption on silicon nitride surface.

The most sensitive optical method of interferometry was exploited for determination of changes in the refractive index following the adsorption of biological molecules onto the solid surface. Instead of having two waveguiding arms (the main and the reference) in traditional Mach-Zhender interferometer, two ortogonal TM and TE modes propagating through the SiO(2)-Si(3)N(4)-SiO(2) waveguide structure were employed in planar polarization interferometer (PPI). Multiperiodic PPI response was, therefore, formed due to the phase shift between TM and TE modes. A matrix simulation procedure was developed in order to investigate the influence of both the refractive index and molecular layer thickness on the PPI response. Nonspecifical binding of fibrinogen to silicon nitride surface was studied as a model object for PPI testing. The results obtained are in good agreement with the known information about fibrinogen adsorption on the different surfaces. An attempt to introduce the concept of 'surface molecular concentration and molecular polariziability' instead of 'molecular layer thickness and refractivity' was undertaken.

Adsorption↗
PubMed2004

Reduction of erythrocyte deformability in rats with cerebral ischemia.

Erythrocyte deformability was studied by laser interferometry in rats with cerebral ischemia. Ninety minutes after ligation of both common carotid arteries the erythrocyte deformability coefficient decreased by 11+/-2% in experimental group in comparison with the baseline level and by 12% in comparison with sham-operated animals and remained 16% decreased after 4 days.

Animals↗
PubMed1978

Dynamics of the amphibian middle ear.

Using laser speckle interferometry, we show that the directional information of acoustic signals is encoded in the motion of eardrum. Moreover, the frequency sensitivity of the auditory system is determined by the mechanical properties of the middle ear, which acts like a damped resonator.

Animals↗
PubMed1997

Kinesin hydrolyses one ATP per 8-nm step.

Kinesin is a two-headed, ATP-dependent motor protein that moves along microtubules in discrete steps of 8 nm. In vitro, single molecules produce processive movement; motors typically take approximately 100 steps before releasing from a microtubule. A central question relates to mechanochemical coupling in this enzyme: how many molecules of ATP are consumed per step? For the actomyosin system, experimental approaches to this issue have generated considerable controversy. Here we take advantage of the processivity of kinesin to determine the coupling ratio without recourse to direct measurements of ATPase activity, which are subject to large experimental uncertainties. Beads carrying single molecules of kinesin moving on microtubules were tracked with high spatial and temporal resolution by interferometry. Statistical analysis of the intervals between steps at limiting ATP, and studies of fluctuations in motor speed as a function of ATP concentration, allow the coupling ratio to be determined. At near-zero load, kinesin molecules hydrolyse a single ATP molecule per 8-nm advance. This finding excludes various one-to-many and many-to-one coupling schemes, analogous to those advanced for myosin, and places severe constraints on models for movement.

Adenosine Triphosphate↗
PubMed1990

Precorneal residence times of sodium hyaluronate solutions studied by quantitative gamma scintigraphy.

Sodium hyaluronate solutions have been advocated in the management of a variety of dry-eye states. By virtue of their non-Newtonian rheological properties, formulations exhibiting high zero-shear viscosities may be used as an artificial tear with the expectation of prolonged precorneal residence times and improved tolerance. Quantitative gamma scintigraphy was used to evaluate the residence times of 0.2% and 0.3% sodium hyaluronate solutions and a polymer-free solution of buffered saline in 12 patients with keratoconjunctivitis sicca and a group of six normal volunteers. Using several indices of residence time, mean values for the sodium hyaluronate solutions were significantly longer than those for buffered saline. Parallel changes in tear film thickness were also demonstrated using a technique based on laser interferometry.

Adhesiveness↗
PubMed1993

Changes in visual function with normal ageing, cataract and intraocular lenses.

We have been able to separate the neural and optical components of vision with contrast sensitivity tests employing laser interferometry and direct viewing of a cathode ray tube display. In normal ageing, neural function declined markedly while optical function remained essentially unchanged. On the other hand, even the mildest degree of cataract was shown to degrade optical function to the extent that it exceeded the age-related neural deterioration. The satisfactory optical performance of the monofocal implant lens has been confirmed, though the diffractive bifocal implant lens was shown to have optical limitations. A major cause of these was shown, by simulation experiments, to be the dilution of the contrast of the in-focus image by the superimposed defocused image, particularly under conditions of reduced retinal sensitivity as would be present in the elderly.

Adolescent↗
PubMed2006

Coherent motion of stereocilia assures the concerted gating of hair-cell transduction channels.

The hair cell's mechanoreceptive organelle, the hair bundle, is highly sensitive because its transduction channels open over a very narrow range of displacements. The synchronous gating of transduction channels also underlies the active hair-bundle motility that amplifies and tunes responsiveness. The extent to which the gating of independent transduction channels is coordinated depends on how tightly individual stereocilia are constrained to move as a unit. Using dual-beam interferometry in the bullfrog's sacculus, we found that thermal movements of stereocilia located as far apart as a hair bundle's opposite edges showed high coherence and negligible phase lag. Because the mechanical degrees of freedom of stereocilia are strongly constrained, a force applied anywhere in the hair bundle deflects the structure as a unit. This feature assures the concerted gating of transduction channels that maximizes the sensitivity of mechanoelectrical transduction and enhances the hair bundle's capacity to amplify its inputs.

Animals↗
PubMed1996

A holographic study of variations in bone deformations resulting from different headgear forces in a macerated human skull.

The effects of headgear on maxillary displacement and the resulting growth modifications are not completely understood, especially regarding the complex relationships between initial and secondary skeletal reactions on one hand and the influence of the direction and magnitude of the applied force on the other. The aim of the present investigation was to study, by means of holographic interferometry, the initial bone displacement occurring in response to headgear traction applied at different force magnitudes and in different directions. Orthopedic forces of 560 grams and orthodontic forces of 354 grams were stimulated on a macerated human skull. The forces came from from high-, straight-, and low-pull headgear traction directed above, through, and below the center of resistance of the maxillary first permanent molars. Immediate skeletal changes were recorded by laser holography. Initial displacements of the maxilla and zygomatic arch in both horizontal and vertical planes were evaluated on frontal and lateral holograms. In most cases, both force magnitudes caused substantial displacements in both planes, albeit to different extents. Complex bending, and rotational, translational, and relative displacements were observed. The direction of displacement did not strictly coincide with that of the applied force. The results of this study indicate that both orthodontic and orthopedic headgear traction may lead to complex initial three-dimensional skeletal displacement in directions not always corresponding with the direction of the applied force.

Biomechanical Phenomena↗