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Biomedical subjects

Adolf F Fercher

Publications and source records attributed to Adolf F Fercher.

12 recordsLinked to original sources
PubMed2005

Three-dimensional ultrahigh-resolution optical coherence tomography of macular diseases.

PURPOSE: To demonstrate a new generation of three-dimensional (3-D) ultrahigh-resolution optical coherence tomography (UHR OCT) technology for visualization of macular diseases. METHODS: One hundred forty eyes with a distinct disease in each of the posterior pole compartments were examined with 3-D UHR OCT. 3-D imaging was performed with a high axial resolution of 3 mum with a compact, commercially available, ultra-broad-bandwidth (160 nm) titanium:sapphire laser at a video rate of up to 25 B-scans/s. Each tomogram consisted of 1024 x 1024 pixels, resulting in 25 megavoxels/s. RESULTS: 3-D UHR OCT offers high-precision 3-D visualization of macular diseases at all structural levels. The UHR modality allows identification of the contour of the hyaloid membrane, tractive forces of epiretinal membranes, and changes within the inner limiting membrane. The system provides quality 3-D images of the topographic dynamics of traction lines from the retinal surface down to the level of the photoreceptor segments. Intraretinal diseases are identified by their specific location in different layers of the neurosensory ultrastructure. Photoreceptor inner and outer segments are clearly delineated in configuration and size, with a characteristic peak in the subfoveal area. The microarchitecture of choroidal neovascularization is distinctly imaged, related leakage can be identified, and the volume can be quantified. CONCLUSIONS: High-speed UHR OCT offers unprecedented, realistic, 3-D imaging of ocular diseases at all epi-, intra- and subretinal levels. A complete 3-D data set of the macular layers allows a comprehensive analysis of focal and diffuse diseases, as well as identification of dynamic pathomechanisms.

Diagnostic Techniques, Ophthalmological↗
PubMed2004

Real-time measurement of in vitro flow by Fourier-domain color Doppler optical coherence tomography.

The possibility of measuring a full Doppler flow depth profile in parallel by use of frequency-domain optical coherence tomography is demonstrated. The method is based on a local phase analysis of the backscattered signal and allows for imaging of bidirectional Doppler flow. The Doppler frequency limit is 5 kHz for the presented measurements and is set by half of the frame rate of the CCD detector array. We measured the flow of 0.3-microm microspheres suspended in distilled water at controlled flow rates and in vitro human blood flow through a 200-microm capillary with a real-time color-encoded Doppler tomogram rate of 2-3/s.

Blood Cells↗
PubMed2003

Phase-shifting algorithm to achieve high-speed long-depth-range probing by frequency-domain optical coherence tomography.

Standard Fourier-domain optical coherence tomography (FDOCT) suffers from the presence of autocorrelation terms that obscure the object information and degrade the sensitivity and signal-to-noise ratio. By exploiting the phase information of the recorded interferograms, it is possible to remove those autocorrelation terms and to double the measurement range. However, standard phase-retrieval algorithms need three to five interferograms. We present a novel technique that shows all the features of complex FDOCT with only two recorded interferograms.

Algorithms↗
PubMed2003

Enhanced visualization of macular pathology with the use of ultrahigh-resolution optical coherence tomography.

OBJECTIVES: To demonstrate a new generation of ophthalmic optical coherence tomography (OCT) technology with unprecedented axial resolution for enhanced imaging of intraretinal microstructures and to investigate its clinical feasibility to visualize intraretinal morphology of macular pathology. METHODS: A clinically viable ultrahigh-resolution ophthalmic OCT system was developed and used in clinical imaging for the first time. Fifty-six eyes of 40 selected patients with different macular diseases including macular hole, macular edema, age-related macular degeneration, central serous chorioretinopathy, epiretinal membranes, and detachment of pigment epithelium and sensory retina were included. OUTCOME MEASURES: Ultrahigh-resolution tomograms visualizing intraretinal morphologic features in different retinal diseases. RESULTS: An axial image resolution of approximately 3 micro m was achieved in the eyes examined, nearly 2 orders of magnitude better than conventional ophthalmic ultrasound. Ultrahigh-resolution OCT images provided additional diagnostically important information on intraretinal morphologic features that could not have been obtained by standard techniques. CONCLUSIONS: Ultrahigh-resolution ophthalmic OCT enables unprecedented visualization of intraretinal morphologic features and therefore has the potential to contribute to a better understanding of ocular pathogenesis, as well as to enhance the sensitivity and specificity for early ophthalmic diagnosis and to monitor the efficacy of therapy. This study establishes a baseline for the interpretation of ultrahigh-resolution ophthalmic OCT imaging of macular diseases.

Adult↗
PubMed2003

Speckle reduction in optical coherence tomography by frequency compounding.

We are investigating the possibility of a frequency compounding method for speckle reduction in optical coherence tomography. The method is based on incoherent summation of the magnitudes of two independent interferometric signals, which were recorded at two different center wavelengths simultaneously. We derive the corresponding statistics and compare the theoretical results with measurements obtained in a uniformly scattering sample. Finally we demonstrate our method by comparing images of human skin recorded in vivo with and without frequency compounding. The compounding method results in an increased contrast and improved image quality without loss of resolution.

Algorithms↗
PubMed2002

Quantitative performance of bifocal and multifocal intraocular lenses in a model eye: point spread function in multifocal intraocular lenses.

OBJECTIVE: To compare the optical properties of bifocal diffractive and multifocal refractive intraocular lenses. METHODS: A model eye with a pupil 4.5 mm in diameter was used to determine the point spread function (PSF) of the distance focus and near focus of a diffractive bifocal intraocular lens (IOL) (model 811E; Pharmacia Inc, Columbus, Ohio) and of a refractive multifocal IOL (model SA40N; Allergan Optical Inc, Irvine, Calif) to compare them with PSFs of foci of corresponding monofocal lenses. For interpreting the PSFs the through focus response, the modulation transfer function, and the Strehl ratio were evaluated. RESULTS: The intensity of the distance focus of the bifocal diffractive lens reached 58.5% and the near focus attained 42.7% of the intensity of a corresponding monofocal lens. The maximal halo intensity surrounding both foci was approximately 4.5%. The distance peak of the refractive multifocal IOL was 73.4% and the near peak 25.1% of a corresponding monofocal lens. The out-of-focus image overlaying the distance focus of the refractive multifocal IOL was approximately 3% of the light intensity of the distance focus, whereas the PSF of the near focus of the multifocal IOL is substantially affected by out-of-focus images. The computed modulation transfer functions show better results for the monofocal lenses, similar results for the tested distance foci, and clear advantages for the bifocal diffractive near focus. CONCLUSIONS: Modulation transfer functions reveal comparable properties for distance vision and a superiority of the bifocal diffractive lens over the refractive multifocal lens for near vision.

Eye↗
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

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↗
PubMed2002

In vivo human retinal imaging by Fourier domain optical coherence tomography.

We present what is to our knowledge the first in vivo tomograms of human retina obtained by Fourier domain optical coherence tomography. We would like to show that this technique might be as powerful as other optical coherence tomography techniques in the ophthalmologic imaging field. The method, experimental setup, data processing, and images are discussed.

Adult↗
PubMedDate not supplied

Ultrahigh resolution optical coherence tomography of macular holes.

PURPOSE: To evaluate ultrahigh resolution optical coherence tomography (UHR OCT) for visualization of intraretinal layers, especially the photoreceptor inner segment and outer segment layers, in eyes with macular holes and after surgical intervention. METHODS: An UHR OCT system based on a titanium:sapphire laser was used, enabling in vivo cross-sectional retinal imaging with 3-micro m axial resolution. Typical, representative tomograms of 5 of 48 eyes from 36 patients demonstrated the potential of UHR OCT to detect morphologic changes in different stages of full-thickness macular holes and changes induced by surgical intervention. RESULTS: UHR OCT could detect subtle intraretinal changes in macular hole formation. Unprecedented visualization of photoreceptor impairment was achieved that appeared to be more extensive than the hole itself. Postoperatively, clinically closed holes showed restoration of the photoreceptor inner and outer segment layers of various extents, with residual disease in some eyes. CONCLUSION: In macular holes, UHR OCT allows for detection of even small morphologic changes of the retinal layers, especially the photoreceptor inner and outer segment layers. Therefore, it also represents a superior method to monitor the effect of surgical interventions. Preoperative photoreceptor impairment and the degree of postoperative restoration could possibly be associated with visual function. Hence, UHR OCT could lead to better understanding of macular hole pathogenesis and to more accurate disease prognosis.

Aged↗
PubMedDate not supplied

Measurement and imaging of birefringent properties of the human cornea with phase-resolved, polarization-sensitive optical coherence tomography.

Optical coherence tomography (OCT) is an emerging technology for high-resolution, noncontact imaging of transparent and scattering media. Polarization-sensitive optical coherence tomography (PS-OCT) is a functional extension of OCT that can image birefringent properties of a biological sample. PS-OCT was used to measure and image retardation and birefringent axis orientation of in vitro human cornea. We used a two-channel PS-OCT system employing a phase-sensitive recording of the interferometric signals in two orthogonal polarization channels. Using an algorithm based on a Hilbert transform, it is possible to calculate the retardation and the slow axis orientation of the sample with only a single A-scan per transversal measurement location. While the retardation information is encoded in the amplitude ratio of the two interferometric signals, the axis orientation is encoded entirely in their phase difference. We present maps of retardation and the distribution of slow axis orientation of the human cornea in longitudinal cross-sections and en face images obtained at the back surface of the cornea. The retardation increases in a radial direction and with depth; the slow axis varies in the transversal direction. Knowledge of the retardation and the slow axis distribution of the cornea might improve nerve fiber polarimetry for glaucoma diagnostics and could be useful for diagnosing different types of pathologies of the cornea.

Birefringence↗