1. Daniel X. Hammer

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    1. Mentioned In 51 Articles

    2. Label-free adaptive optics imaging of human retinal macrophage distribution and dynamics

      Label-free adaptive optics imaging of human retinal macrophage distribution and dynamics
      Microglia are resident central nervous system macrophages and the first responders to neural injury. Until recently, microglia have been studied only in animal models with exogenous or transgenic labeling. While these studies provided a wealth of information on the delicate balance between neuroprotection and neurotoxicity within which these cells operate, extrapolation to human immune function has remained an open question. Here we examine key characteristics of retinal macrophage cells in ...
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    3. Characterization of New Optical Imaging Biomarkers of Peripheral Nerve Overstimulation

      Characterization of New Optical Imaging Biomarkers of Peripheral Nerve Overstimulation
      An animal study was designed to explore the potentially damaging effects of electrical overstimulation on peripheral nerves using a polarization‐sensitive optical coherence tomography (PS‐OCT) imaging and stimulation platform. Lewis rats (n = 15) were divided into 3 groups with 2 different levels of stimulation applied to the exposed sciatic nerve: Group 1 (sham control): 0.0 mA/0 Hz, Group 2: 3.4 mA/50 Hz, and Group 3 ...
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    4. Application of optical coherence tomography and optical path length method for monitoring corneal thickness and refractive index change during corneal cross-linking

      Application of optical coherence tomography and optical path length method for monitoring corneal thickness and refractive index change during corneal cross-linking
      Corneal cross-linking (CXL) using UVA irradiation with a riboflavin photosensitizer has emerged as a new treatment paradigm for corneal ectatic disorders. The thickness threshold for protection of intraocular structures has often been challenged with ongoing developments, and corneal thinning becomes an important safety concern, especially for patients with thin corneas. In this study with an ex vivo bovine eye model, we monitored corneal thinning and corneal refractive index changes using ...
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    5. Toward optical coherence tomography angiography-based biomarkers to assess the safety of peripheral nerve electrostimulation

      Toward optical coherence tomography angiography-based biomarkers to assess the safety of peripheral nerve electrostimulation
      Objective: Peripheral nerves serve as a link between the central nervous system and its targets. Altering peripheral nerve activity through targeted electrical stimulation is being investigated as a therapy for modulating end organ function. To support rapid advancement in the field, novel approaches to predict and prevent nerve injury resulting from the electrical stimulation must be developed to overcome the limitations of traditional histological methods. The present study aims to ...
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    6. 3-D printed photoreceptor phantoms for evaluating lateral resolution of adaptive optics imaging systems

      3-D printed photoreceptor phantoms for evaluating lateral resolution of adaptive optics imaging systems
      With adaptive optics (AO), optical coherence tomography and scanning laser ophthalmoscopy imaging systems can resolve individual photoreceptor cells in living eyes, due to enhanced lateral spatial resolution. However, no standard test method exists for experimentally quantifying this parameter in ophthalmic AO imagers. Here, we present three-dimensional (3-D) printed phantoms, which enable the measurement of lateral resolution in an anatomically relevant manner. We used two-photon polymerization to fabricate two phantoms, which ...
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    7. Optical coherence tomography angiography based biomarkers to assess the safety of peripheral nerve electrostimulation

      Optical coherence tomography angiography based biomarkers to assess the safety of peripheral nerve electrostimulation
      Peripheral nerves connect and relay information between the central nervous system and its target organs. Small arteries traverse the epineurium and are responsible for supplying blood to the axons and cells within the nerves. Constriction or damage to these vessels can reduce perfusion leading to ischemic insults. Peripheral nerve electrostimulation has been approved for the treatment of epilepsy, depression and migraines, and is also being studied for the treatment of ...
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    8. Optic Nerve Head Measurements With Optical Coherence Tomography: A Phantom-Based Study Reveals Differences Among Clinical Devices

      Optic Nerve Head Measurements With Optical Coherence Tomography: A Phantom-Based Study Reveals Differences Among Clinical Devices
      Purpose : Optical coherence tomography (OCT) can monitor for glaucoma by measuring dimensions of the optic nerve head (ONH) cup and disc. Multiple clinical studies have shown that different OCT devices yield different estimates of retinal dimensions. We developed phantoms mimicking ONH morphology as a new way to compare ONH measurements from different clinical OCT devices. Methods : Three phantoms were fabricated to model the ONH: One normal and two with glaucomatous ...
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    9. Feature of the Week 03/20/2016: Closed Loop Tracked Doppler OCT Based Heart Monitor for the Drosophila Melanogaster Larvae

      Feature of the Week 03/20/2016: Closed Loop Tracked Doppler OCT Based Heart Monitor for the Drosophila Melanogaster Larvae
      A fruit fly larva (top) was continuously tracked for continuous remote monitoring. A heartbeat trace of freely moving larva (bottom) was obtained by a low coherence interferometry based doppler sensing technique. This paper presents a novel instrument for biosciences, useful for studies of moving embryos. A dual sequential imaging/measurement channel is assembled via a closed-loop tracking architecture. The dual channel system can operate in two regimes: (i) single-point Doppler ...
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    10. IMAGING WITH MULTIMODAL ADAPTIVE-OPTICS OPTICAL COHERENCE TOMOGRAPHY IN MULTIPLE EVANESCENT WHITE DOT SYNDROME: THE STRUCTURE AND FUNCTIONAL RELATIONSHIP

      IMAGING WITH MULTIMODAL ADAPTIVE-OPTICS OPTICAL COHERENCE TOMOGRAPHY IN MULTIPLE EVANESCENT WHITE DOT SYNDROME: THE STRUCTURE AND FUNCTIONAL RELATIONSHIP
      Purpose: To elucidate the location of pathological changes in multiple evanescent white dot syndrome (MEWDS) with the use of multimodal adaptive optics (AO) imaging . Methods: A 5-year observational case study of a 24-year-old female with recurrent MEWDS. Full examination included history, Snellen chart visual acuity, pupil assessment, intraocular pressures, slit lamp evaluation, dilated fundoscopic exam, imaging with Fourier-domain optical coherence tomography (FD-OCT), blue-light fundus autofluorescence (FAF), fundus photography, fluorescein angiography ...
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    11. Image quality metrics for optical coherence angiography

      Image quality metrics for optical coherence angiography
      We characterized image quality in optical coherence angiography (OCA)en faceplanes of mouse cortical capillary network in terms of signal-to-noise ratio (SNR) and Weber contrast (Wc) through a novel mask-based segmentation method. The method was used to compare two adjacent B-scan processing algorithms, (1) average absolute difference (AAD) and (2) standard deviation (SD), while varying the number of lateral cross-sections acquired (also known as the gate length, N). AAD and ...
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    12. The use of time-lapse optical coherence tomography to image the effects of microapplied toxins on the retina

      The use of time-lapse optical coherence tomography to image the effects of microapplied toxins on the retina
      Purpose: We developed a novel technique using a drug microperfusion device and time-lapse optical coherence tomography (OCT) for accelerated drug screening and retinotoxin characterization. Methods: Using an ex vivo rabbit eyecup preparation, we studied retinotoxin effects in real-time by microperfusing small retinal areas under a transparent fluoropolymer tube. Known retinotoxic agents were applied to the retina for 5 minute periods while changes in retinal structure, thickness, and reflectance were monitored ...
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  2. About Daniel X. Hammer

    Daniel X. Hammer

    Daniel X. Hammer received a B.S. in Electrical Engineering from Rensselaer Polytechnic Institute in 1991 and M.S. and Ph.D. degrees in Biomedical Engineering from University of Texas at Austin in 1998 and 2001. Dr. Hammer has 20 years experience in the invention, design, development, and application of biomedical optics and instrumentation to a broad range of interdisciplinary research programs. He is co-editor of Advances in Optical Imaging for Clinical Medicine (Wiley) and has 65 peer-reviewed publications, 13 patents and disclosures, and over 150 other papers and publications. He is currently Deputy Director of the Division of Biomedical Physics, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health (CDRH/OSEL/DBP). He is a member of the Ophthalmic Technologies Organization Committee, Photonic West. He is also a member of OSA and SPIE.