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Robert J Zawadzki - One of the best experts on this subject based on the ideXlab platform.

  • review of adaptive optics oct ao oct principles and applications for Retinal Imaging invited
    Biomedical Optics Express, 2017
    Co-Authors: Michael Pircher, Robert J Zawadzki
    Abstract:

    In vivo Imaging of the human retina with a resolution that allows visualization of cellular structures has proven to be essential to broaden our knowledge about the physiology of this precious and very complex neural tissue that enables the first steps in vision. Many pathologic changes originate from functional and structural alterations on a cellular scale, long before any degradation in vision can be noted. Therefore, it is important to investigate these tissues with a sufficient level of detail in order to better understand associated disease development or the effects of therapeutic intervention. Optical Retinal Imaging modalities rely on the optical elements of the eye itself (mainly the cornea and lens) to produce Retinal images and are therefore affected by the specific arrangement of these elements and possible imperfections in curvature. Thus, aberrations are introduced to the Imaging light and image quality is degraded. To compensate for these aberrations, adaptive optics (AO), a technology initially developed in astronomy, has been utilized. However, the axial sectioning provided by Retinal AO-based fundus cameras and scanning laser ophthalmoscope instruments is limited to tens of micrometers because of the rather small available numerical aperture of the eye. To overcome this limitation and thus achieve much higher axial sectioning in the order of 2-5µm, AO has been combined with optical coherence tomography (OCT) into AO-OCT. This enabled for the first time in vivo volumetric Retinal Imaging with high isotropic resolution. This article summarizes the technical aspects of AO-OCT and provides an overview on its various implementations and some of its clinical applications. In addition, latest developments in the field, such as computational AO-OCT and wavefront sensor less AO-OCT, are covered.

  • wavefront sensorless adaptive optics fluorescence biomicroscope for in vivo Retinal Imaging in mice
    Biomedical Optics Express, 2016
    Co-Authors: Daniel J Wahl, Yifan Jian, Stefano Bonora, Robert J Zawadzki, Marinko V Sarunic
    Abstract:

    Cellular-resolution in vivo fluorescence Imaging is a valuable tool for longitudinal studies of Retinal function in vision research. Wavefront sensorless adaptive optics (WSAO) is a developing technology that enables high-resolution Imaging of the mouse retina. In place of the conventional method of using a Shack-Hartmann wavefront sensor to measure the aberrations directly, WSAO uses an image quality metric and a search algorithm to drive the shape of the adaptive element (i.e. deformable mirror). WSAO is a robust approach to AO and it is compatible with a compact, low-cost lens-based system. In this report, we demonstrated a hill-climbing algorithm for WSAO with a variable focus lens and deformable mirror for non-invasive in vivo Imaging of EGFP (enhanced green fluorescent protein) labelled ganglion cells and microglia cells in the mouse retina.

  • wavefront sensorless adaptive optics optical coherence tomography for in vivo Retinal Imaging in mice
    Biomedical Optics Express, 2014
    Co-Authors: Yifan Jian, Jing Xu, Martin A Gradowski, Stefano Bonora, Robert J Zawadzki, Marinko V Sarunic
    Abstract:

    We present wavefront sensorless adaptive optics (WSAO) Fourier domain optical coherence tomography (FD-OCT) for in vivo small animal Retinal Imaging. WSAO is attractive especially for mouse Retinal Imaging because it simplifies optical design and eliminates the need for wavefront sensing, which is difficult in the small animal eye. GPU accelerated processing of the OCT data permitted real-time extraction of image quality metrics (intensity) for arbitrarily selected Retinal layers to be optimized. Modal control of a commercially available segmented deformable mirror (IrisAO Inc.) provided rapid convergence using a sequential search algorithm. Image quality improvements with WSAO OCT are presented for both pigmented and albino mouse Retinal data, acquired in vivo.

  • integrated adaptive optics optical coherence tomography and adaptive optics scanning laser ophthalmoscope system for simultaneous cellular resolution in vivo Retinal Imaging
    Biomedical Optics Express, 2011
    Co-Authors: Robert J Zawadzki, Steven M Jones, Suman Pilli, Sandra Balderasmata, Scot S Olivier, John S Werner
    Abstract:

    We describe an ultrahigh-resolution (UHR) Retinal Imaging system that combines adaptive optics Fourier-domain optical coherence tomography (AO-OCT) with an adaptive optics scanning laser ophthalmoscope (AO-SLO) to allow simultaneous data acquisition by the two modalities. The AO-SLO subsystem was integrated into the previously described AO-UHR OCT instrument with minimal changes to the latter. This was done in order to ensure optimal performance and image quality of the AO- UHR OCT. In this design both Imaging modalities share most of the optical components including a common AO-subsystem and vertical scanner. One of the benefits of combining Fd-OCT with SLO includes automatic co-registration between two acquisition channels for direct comparison between Retinal structures imaged by both modalities (e.g., photoreceptor mosaics or microvasculature maps). Because of differences in the detection scheme of the two systems, this dual Imaging modality instrument can provide insight into Retinal morphology and potentially function, that could not be accessed easily by a single system. In this paper we describe details of the components and parameters of the combined instrument, including incorporation of a novel membrane magnetic deformable mirror with increased stroke and actuator count used as a single wavefront corrector. We also discuss laser safety calculations for this multimodal system. Finally, Retinal images acquired in vivo with this system are presented.

  • cellular resolution volumetric in vivo Retinal Imaging with adaptive optics optical coherence tomography
    Optics Express, 2009
    Co-Authors: Robert J Zawadzki, Stacey S Choi, Alfred R Fuller, Julia W Evans, Bernd Hamann, John S Werner
    Abstract:

    Ultrahigh-resolution adaptive optics–optical coherence tomography (UHR-AO-OCT) instrumentation allowing monochromatic and chromatic aberration correction was used for volumetric in vivo Retinal Imaging of various Retinal structures including the macula and optic nerve head (ONH). Novel visualization methods that simplify AO-OCT data viewing are presented, and include co-registration of AO-OCT volumes with fundus photography and stitching of multiple AO-OCT sub-volumes to create a large field of view (FOV) high-resolution volume. Additionally, we explored the utility of Interactive Science Publishing by linking all presented AO-OCT datasets with the OSA ISP software.

Johannes F. De Boer - One of the best experts on this subject based on the ideXlab platform.

  • Parallel scanning laser ophthalmoscope (PSLO) for high-speed Retinal Imaging
    Investigative Ophthalmology & Visual Science, 2014
    Co-Authors: Kari V. Vienola, Mathivanan Damodaran, Boy Braaf, Koenraad A. Vermeer, Johannes F. De Boer
    Abstract:

    Purpose High-speed Imaging of the retina is crucial for obtaining high quality images in the presence of eye motion. To improve the speed of traditional scanners, a high-speed ophthalmic device is presented using a digital micro-mirror device (DMD) for confocal Imaging with multiple simultaneous spots. Methods The PSLO consists of three parts: an illumination, an Imaging and a detector arm (Fig. 1). The DMD is uniformly illuminated with a near-infrared (850 nm) LED. The separation between ON positioned mirror elements was made large enough to eliminate cross-talk between neighboring virtual pinholes, and therefore allowed multi-spot confocal Imaging across the whole field of view (FOV). The DMD is programmed to project series of shifted point pattern configurations, effectively scanning the spots over the sample surface. The DMD was imaged onto a sample and the returning light was tapped of via a beam-splitter and imaged on a CMOS camera. Multiple point illuminated frames are combined to form one confocal wide-field image. As a proof of principle images of a resolution target were acquired with the PSLO system. Results The resolution target was imaged with a pattern with virtual pinhole size of 2x2 mirrors and the separation between two pinholes was 4 mirror elements. Figure 1B shows the results for combining 9 illumination patterns to form the final image. Conclusions It is possible to create wide-field confocal images with the PSLO system. In theory the DMD can achieve higher frame rates than traditional scanner-based systems by illuminating the sample with multiple spots. In Retinal Imaging, such a setup will provide better images because higher Imaging speeds reduce motion artifacts.

  • Parallel scanning laser ophthalmoscope for Retinal Imaging
    2014
    Co-Authors: Kari V. Vienola, Mathivanan Damodaran, Boy Braaf, Mattijs De Groot, Koenraad A. Vermeer, Johannes F. De Boer
    Abstract:

    Introduction High-speed Imaging of the retina is crucial for obtaining high quality images in the presence of eye motion. To improve the speed of traditional scanners, a high-speed ophthalmic device is presented using a digital micro-mirror device (DMD) for confocal Imaging with multiple simultaneous spots. Methods An experimental ophthalmic Imaging system was constructed based on an 850 nm LED and a DMD containing 1024 x 768 micro-mirrors. Single mirror elements are sparsely turned ON to create multiple spots over the whole field of view. The DMD is programmed to project series of shifted point pattern configurations, effectively scanning the spots over the sample surface. The backscattered light from the retina is tapped off via a beam-splitter and imaged onto a CMOS camera. A confocal image is constructed by applying an image mask of virtual pinholes to each recorded frame. A wide-field confocal image is then created by combining all frames in a single image. Results In the figure a dollar note was imaged with all mirrors ON (widefield) and with multiple spots configuration (every 100th mirror ON). In widefield mode light is detected from different planes above and below the focal plane. When using multiple spots and virtual pinholes, only light from the focal plane is detected. The image on the right shows clearly the microstructure of the bank note. Conclusions It is possible to create confocal images with the PSLO system. In theory the DMD can achieve higher frame rates than traditional scanner-based systems (> 2 kHz) by illuminating the sample with multiple spots.

  • ultrahigh resolution high speed Retinal Imaging using spectral domain optical coherence tomography
    Optics Express, 2004
    Co-Authors: Barry Cense, Nader Nassif, Teresa C Chen, Mark C Pierce, Hyle B Park, Brett E Bouma, Guillermo J Tearney, Johannes F. De Boer
    Abstract:

    We present the first ultrahigh-resolution optical coherence tomography (OCT) structural intensity images and movies of the human retina in vivo at 29.3 frames per second with 500 A-lines per frame. Data was acquired at a continuous rate of 29,300 spectra per second with a 98% duty cycle. Two consecutive spectra were coherently summed to improve sensitivity, resulting in an effective rate of 14,600 A-lines per second at an effective integration time of 68 µs. The turn-key source was a combination of two super luminescent diodes with a combined spectral width of more than 150 nm providing 4.5 mW of power. The spectrometer of the spectral-domain OCT (SD-OCT) setup was centered around 885 nm with a bandwidth of 145 nm. The effective bandwidth in the eye was limited to approximately 100 nm due to increased absorption of wavelengths above 920 nm in the vitreous. Comparing the performance of our ultrahighresolution SD-OCT system with a conventional high-resolution time domain OCT system, the A-line rate of the spectral-domain OCT system was 59 times higher at a 5.4 dB lower sensitivity. With use of a software based dispersion compensation scheme, coherence length broadening due to dispersion mismatch between sample and reference arms was minimized. The coherence length measured from a mirror in air was equal to 4.0 µm (n=1). The coherence length determined from the specular reflection of the foveal umbo in vivo in a healthy human eye was equal to 3.5 µm (n=1.38). With this new system, two layers at the location of the Retinal pigmented epithelium seem to be present, as well as small features in the inner and outer plexiform layers, which are believed to be small blood vessels.

  • in vivo human Retinal Imaging by ultrahigh speed spectral domain optical coherence tomography
    Optics Letters, 2004
    Co-Authors: Nader Nassif, Barry Cense, Teresa C Chen, Hyle B Park, Brett E Bouma, Guillermo J Tearney, Johannes F. De Boer
    Abstract:

    An ultrahigh-speed spectral domain optical coherence tomography (SD-OCT) system is presented that achieves acquisition rates of 29,300 depth profiles/s. The sensitivity of SD-OCT and time domain OCT (TD-OCT) are experimentally compared, demonstrating a 21.7-dB improvement of SD-OCT over TD-OCT. In vivo images of the human retina are presented, demonstrating the ability to acquire high-quality structural images with an axial resolution of 6 µm at ultrahigh speed and with an ocular exposure level of less than 600 µW.

Stephen A. Burns - One of the best experts on this subject based on the ideXlab platform.

  • Lasers in Retinal Imaging
    Frontiers in Optics, 2014
    Co-Authors: Stephen A. Burns
    Abstract:

    Lasers were used in measuring the optical quality of the eye as early as 1965, but it was about 1980 that they really began to impact Retinal Imaging. This talk describes the advancements in Retinal Imaging that have occurred over the last 35 years and the role lasers played in this development.

  • the use of forward scatter to improve Retinal vascular Imaging with an adaptive optics scanning laser ophthalmoscope
    Biomedical Optics Express, 2012
    Co-Authors: Toco Yuen Ping Chui, Dean A Vannasdale, Stephen A. Burns
    Abstract:

    Retinal vascular diseases are a leading cause of blindness and visual disability. The advent of adaptive optics Retinal Imaging has enabled us to image the Retinal vascular at cellular resolutions, but Imaging of the vasculature can be difficult due to the complex nature of the images, including features of many other Retinal structures, such as the nerve fiber layer, glial and other cells. In this paper we show that varying the size and centration of the confocal aperture of an adaptive optics scanning laser ophthalmoscope (AOSLO) can increase sensitivity to multiply scattered light, especially light forward scattered from the vasculature and erythrocytes. The resulting technique was tested by Imaging regions with different Retinal tissue reflectivities as well as within the optic nerve head.

  • adaptive optics scanning laser ophthalmoscope with integrated wide field Retinal Imaging and tracking
    Journal of The Optical Society of America A-optics Image Science and Vision, 2010
    Co-Authors: Daniel R Ferguson, Daniel X Hammer, Mircea Mujat, Zhangyi Zhong, Ankit H Patel, Cong Deng, Stephen A. Burns
    Abstract:

    We have developed a new, unified implementation of the adaptive optics scanning laser ophthalmoscope (AOSLO) incorporating a wide-field line-scanning ophthalmoscope (LSO) and a closed-loop optical Retinal tracker. AOSLO raster scans are deflected by the integrated tracking mirrors so that direct AOSLO stabilization is automatic during tracking. The wide-field imager and large-spherical-mirror optical interface design, as well as a large-stroke deformable mirror (DM), enable the AOSLO image field to be corrected at any Retinal coordinates of interest in a field of >25 deg. AO performance was assessed by Imaging individuals with a range of refractive errors. In most subjects, image contrast was measurable at spatial frequencies close to the diffraction limit. Closed-loop optical (hardware) tracking performance was assessed by comparing sequential image series with and without stabilization. Though usually better than 10 μm rms, or 0.03 deg, tracking does not yet stabilize to single cone precision but significantly improves average image quality and increases the number of frames that can be successfully aligned by software-based post-processing methods. The new optical interface allows the high-resolution Imaging field to be placed anywhere within the wide field without requiring the subject to re-fixate, enabling easier Retinal navigation and faster, more efficient AOSLO montage capture and stitching.

  • adaptive optics scanning laser ophthalmoscope for stabilized Retinal Imaging
    Optics Express, 2006
    Co-Authors: Daniel X Hammer, Daniel R Ferguson, Chad E Bigelow, Nicusor Iftimia, Teoman E Ustun, Stephen A. Burns
    Abstract:

    A Retinal Imaging instrument that integrates adaptive optics (AO), scanning laser ophthalmoscopy (SLO), and Retinal tracking components was built and tested. The system uses a Hartmann-Shack wave-front sensor (HS-WS) and MEMS-based deformable mirror (DM) for AO-correction of high-resolution, confocal SLO images. The system includes a wide-field line-scanning laser ophthalmoscope for easy orientation of the high-magnification SLO raster. The AO system corrected ocular aberrations to <0.1 μm RMS wave-front error. An active Retinal tracking with custom processing board sensed and corrected eye motion with a bandwidth exceeding 1 kHz. We demonstrate tracking accuracy down to 6 μm RMS for some subjects (typically performance: 10–15 μm RMS). The system has the potential to become an important tool to clinicians and researchers for vision studies and the early detection and treatment of Retinal diseases.

Donald T Miller - One of the best experts on this subject based on the ideXlab platform.

  • adaptive optics optical coherence tomography with dynamic Retinal tracking
    Biomedical Optics Express, 2014
    Co-Authors: Omer P Kocaoglu, Daniel X Hammer, Daniel R Ferguson, Ravi S Jonnal, Qiang Wang, Donald T Miller
    Abstract:

    Adaptive optics optical coherence tomography (AO-OCT) is a highly sensitive and noninvasive method for three dimensional Imaging of the microscopic retina. Like all in vivo Retinal Imaging techniques, however, it suffers the effects of involuntary eye movements that occur even under normal fixation. In this study we investigated dynamic Retinal tracking to measure and correct eye motion at KHz rates for AO-OCT Imaging. A customized retina tracking module was integrated into the sample arm of the 2nd-generation Indiana AO-OCT system and images were acquired on three subjects. Analyses were developed based on temporal amplitude and spatial power spectra in conjunction with strip-wise registration to independently measure AO-OCT tracking performance. After optimization of the tracker parameters, the system was found to correct eye movements up to 100 Hz and reduce residual motion to 10 µm root mean square. Between session precision was 33 µm. Performance was limited by tracker-generated noise at high temporal frequencies.

  • adaptive optics flood illumination camera for high speed Retinal Imaging
    Optics Express, 2006
    Co-Authors: Ravi S Jonnal, Karen E Thorn, Junle Qu, Yan Zhang, Donald T Miller
    Abstract:

    Current adaptive optics flood-illumination retina cameras operate at low frame rates, acquiring Retinal images below seven Hz, which restricts their research and clinical utility. Here we investigate a novel bench top flood-illumination camera that achieves significantly higher frame rates using strobing fiber-coupled superluminescent and laser diodes in conjunction with a scientific-grade CCD. Source strength was sufficient to obviate frame averaging, even for exposures as short as 1/3 msec. Continuous frame rates of 10, 30, and 60 Hz were achieved for Imaging 1.8, 0.8, and 0.4 deg Retinal patches, respectively. Short-burst Imaging up to 500 Hz was also achieved by temporarily storing sequences of images on the CCD. High frame rates, short exposure durations (1 msec), and correction of the most significant aberrations of the eye were found necessary for individuating Retinal blood cells and directly measuring cellular flow in capillaries. Cone videos of dark adapted eyes showed a surprisingly rapid fluctuation (~1 Hz) in the reflectance of single cones. As further demonstration of the value of the camera, we evaluated the tradeoff between exposure duration and image blur associated with retina motion.

  • Adaptive optics high resolution Retinal Imaging
    Optics InfoBase Conference Papers, 2006
    Co-Authors: Donald T Miller
    Abstract:

    Adaptive optics cameras based on flood illumination and optical coherence tomography have been developed and applied to Imaging the cellular retina. The cameras have led to new insights into the optical properties of photoreceptor cells. © 2006 Optical Society of America.

  • supernormal vision and high resolution Retinal Imaging through adaptive optics
    Journal of The Optical Society of America A-optics Image Science and Vision, 1997
    Co-Authors: J. Liang, David R Williams, Donald T Miller
    Abstract:

    Even when corrected with the best spectacles or contact lenses, normal human eyes still suffer from monochromatic aberrations that blur vision when the pupil is large. We have successfully corrected these aberrations using adaptive optics, providing normal eyes with supernormal optical quality. Contrast sensitivity to fine spatial patterns was increased when observers viewed stimuli through adaptive optics. The eye’s aberrations also limit the resolution of images of the retina, a limit that has existed since the invention of the ophthalmoscope. We have constructed a fundus camera equipped with adaptive optics that provides unprecedented resolution, allowing the Imaging of microscopic structures the size of single cells in the living human retina. © 1997 Optical Society of America [S0740-3232(97)01111-3]

  • Supernormal vision and high-resolution Retinal Imaging through adaptive optics.
    Journal of the Optical Society of America. A, Optics, image science, and vision, 1997
    Co-Authors: J. Liang, D. R. Williams, Donald T Miller
    Abstract:

    Even when corrected with the best spectacles or contact lenses, normal human eyes still suffer from monochromatic aberrations that blur vision when the pupil is large. We have successfully corrected these aberrations using adaptive optics, providing normal eyes with supernormal optical quality. Contrast sensitivity to fine spatial patterns was increased when observers viewed stimuli through adaptive optics. The eye's aberrations also limit the resolution of images of the retina, a limit that has existed since the invention of the ophthalmoscope. We have constructed a fundus camera equipped with adaptive optics that provides unprecedented resolution, allowing the Imaging of microscopic structures the size of single cells in the living human retina.

John S Werner - One of the best experts on this subject based on the ideXlab platform.

  • integrated adaptive optics optical coherence tomography and adaptive optics scanning laser ophthalmoscope system for simultaneous cellular resolution in vivo Retinal Imaging
    Biomedical Optics Express, 2011
    Co-Authors: Robert J Zawadzki, Steven M Jones, Suman Pilli, Sandra Balderasmata, Scot S Olivier, John S Werner
    Abstract:

    We describe an ultrahigh-resolution (UHR) Retinal Imaging system that combines adaptive optics Fourier-domain optical coherence tomography (AO-OCT) with an adaptive optics scanning laser ophthalmoscope (AO-SLO) to allow simultaneous data acquisition by the two modalities. The AO-SLO subsystem was integrated into the previously described AO-UHR OCT instrument with minimal changes to the latter. This was done in order to ensure optimal performance and image quality of the AO- UHR OCT. In this design both Imaging modalities share most of the optical components including a common AO-subsystem and vertical scanner. One of the benefits of combining Fd-OCT with SLO includes automatic co-registration between two acquisition channels for direct comparison between Retinal structures imaged by both modalities (e.g., photoreceptor mosaics or microvasculature maps). Because of differences in the detection scheme of the two systems, this dual Imaging modality instrument can provide insight into Retinal morphology and potentially function, that could not be accessed easily by a single system. In this paper we describe details of the components and parameters of the combined instrument, including incorporation of a novel membrane magnetic deformable mirror with increased stroke and actuator count used as a single wavefront corrector. We also discuss laser safety calculations for this multimodal system. Finally, Retinal images acquired in vivo with this system are presented.

  • cellular resolution volumetric in vivo Retinal Imaging with adaptive optics optical coherence tomography
    Optics Express, 2009
    Co-Authors: Robert J Zawadzki, Stacey S Choi, Alfred R Fuller, Julia W Evans, Bernd Hamann, John S Werner
    Abstract:

    Ultrahigh-resolution adaptive optics–optical coherence tomography (UHR-AO-OCT) instrumentation allowing monochromatic and chromatic aberration correction was used for volumetric in vivo Retinal Imaging of various Retinal structures including the macula and optic nerve head (ONH). Novel visualization methods that simplify AO-OCT data viewing are presented, and include co-registration of AO-OCT volumes with fundus photography and stitching of multiple AO-OCT sub-volumes to create a large field of view (FOV) high-resolution volume. Additionally, we explored the utility of Interactive Science Publishing by linking all presented AO-OCT datasets with the OSA ISP software.