Wolf Harmening

Wolf Harmening
University of Bonn | Uni Bonn · Department of Ophthalmology

PhD

About

63
Publications
12,313
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753
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Introduction
Wolf Harmening currently works at the Department of Ophthalmology, University of Bonn. Wolf does research in Ophthalmology, Psychophysics and Neuroscience. Their current project is 'Single cell psychophysics'.

Publications

Publications (63)
Article
Full-text available
Fixational eye movements are a hallmark of human gaze behavior, yet little is known about how they interact between fellow eyes. Here, we designed, built and validated a split-field binocular scanning laser ophthalmoscope to record high-resolution eye motion traces from both eyes of six observers during fixation in different binocular vergence cond...
Article
Full-text available
The foveal cone mosaic can be directly visualized using adaptive optics scanning light ophthalmoscopy (AOSLO). Previous studies in individuals with normal vision report wide variability in the topography of the foveal cone mosaic, especially the value of peak cone density (PCD). While these studies often involve a human grader, there have been no s...
Preprint
Full-text available
Perception and action are inherently entangled: our world view is shaped by how we explore and navigate our environment through complex and variable self-motion. Even when fixating on a stable stimulus, our eyes undergo small, involuntary movements. Fixational eye movements (FEM) render a stable world jittery on our retinae, which contributes noise...
Article
Purpose To investigate foveal photoreceptor configuration in Alport syndrome, a rare inherited disease characterized by Collagen IV dysfunction. Methods Adaptive optics scanning laser ophthalmoscope (AOSLO) in vivo imaging of the foveal center and quantitative analysis of cone photoreceptor topography in a 17-year-old male patient with Alport synd...
Preprint
Fixational eye motion is a hallmark of human gaze behavior, yet little is known about how it interacts between fellow eyes. Here, we designed, build and validated a split-field binocular scanning laser ophthalmoscope (bSLO) to record high-resolution eye motion traces from both eyes of six observers during fixation at different binocular vergence co...
Chapter
Genetic diseases affecting the retina are highly heterogeneous. Although fundoscopy remains a diagnostic mainstay, retinal imaging provides additional important information and has become an essential part of the management of these conditions. These in vivo imaging techniques have rapidly evolved over the past decades due to advances in electronic...
Article
The small physical depression of the human retina, the fovea, is the retinal locus of prime visual resolution, achieved by a peaking topography of the light-sensitive cone photoreceptor outer segments1, 2, 3 and a post-receptor wiring scheme preserving high-density sampling.⁴,⁵ Humans dynamically direct their gaze such that the retinal images of ob...
Article
Full-text available
Purpose: The cellular topography of the human foveola, the central 1° diameter of the fovea, is strikingly non-uniform, with a steep increase of cone photoreceptor density and outer segment (OS) length toward its center. Here, we assessed to what extent the specific cellular organization of the foveola of an individual is reflected in visual sensit...
Article
William Tuten and Wolf Harmening introduce the anatomical and functional signatures of foveated vision in humans.
Preprint
Full-text available
The small physical depression of the human retina, termed fovea, is the functional center of human vision, providing an acute sense of visual space and color, but it is yet unclear if the exact arrangement of the few thousand photoreceptors at the foveal center is relevant for visual behavior. By employing adaptive optics in vivo imaging and micro-...
Preprint
Full-text available
Humans direct their gaze towards visual objects of interest such that the retinal images of fixated objects fall onto the fovea, a small anatomically and physiologically specialized region of the retina displaying highest visual fidelity. One striking anatomical feature of the fovea is its non-uniform cellular topography, with a steep decline of co...
Article
The spatial and spectral topography of the cone mosaic set the limits for detection and discrimination of chromatic sinewave gratings. Here, we sought to compare the spatial characteristics of mechanisms mediating hue perception against those mediating chromatic detection in individuals with known spectral topography and with optical aberrations re...
Article
Full-text available
Multi-wavelength ophthalmic imaging and stimulation of photoreceptor cells require consideration of chromatic dispersion of the eye, manifesting in longitudinal and transverse chromatic aberrations. Contemporary image-based techniques to measure and correct transverse chromatic aberration (TCA) and the resulting transverse chromatic offset (TCO) in...
Chapter
Full-text available
Photoreceptors in the retina constitute the cellular building blocks of the initial stage of vision. To isolate the contribution of a single cell to any percept is quite challenging because normal ocular optics and motion distributes light from small stimuli over many photoreceptors. Recent microstimulation techniques coupled with adaptive optics s...
Article
Full-text available
To assess whether the eye's optical imperfections are relevant for hyperacute vision, we measured ocular wave aberrations, visual hyperacuity, and acuity thresholds in 31 eyes of young adults. Although there was a significant positive correlation between the subjects' performance in Vernier- and Landolt-optotype acuity tasks, we found clear differe...
Preprint
Full-text available
Multi-wavelength ophthalmic imaging and stimulation of photoreceptor cells requires consideration of chromatic dispersion of the eye, manifesting in longitudinal and transverse chromatic aberrations. Current image-based techniques to measure and correct transverse chromatic aberration (TCA) and the resulting transverse chromatic offset (TCO) in an...
Article
Aim of the study was to compare optical coherence tomography angiography (OCT-A)and conventional fluorescein angiography (FA)for quantitative analysis of the retinal and choroidal vasculature in the animal model of laser-induced choroidal neovascularization (CNV). Therefore, Dark Agouti rats underwent argon laser photocoagulation to induce CNV at D...
Article
Full-text available
Due to the enormous dynamic range of human photoreceptors in response to light, studying their visual function in the intact retina challenges the stimulation hardware, specifically with regard to the displayable luminance contrast. The adaptive optics scanning laser ophthalmoscope (AOSLO) is an optical platform that focuses light to extremely smal...
Article
Full-text available
Background: Recent years have seen a marked increase in laser-pointerrelated injuries, which sometimes involve severe retinal damage and irreversible visual impairment. These injuries are often caused by untested or incorrectly classified devices that are freely available over the Internet. Methods: We reviewed pertinent publications retrieved b...
Article
Full-text available
Purpose: To determine the minimal optical coherence tomography B-scan density for reliable detection of intraretinal and subretinal fluid. Methods: Spectral domain optical coherence tomography raster scanning (Spectralis; Heidelberg Engineering, Heidelberg, Germany) using a scan field of 20° × 20° of 97 B-scans with an interscan distance (ISD) o...
Article
Full-text available
Aremarkable feature of human vision is that the retina and brain have evolved circuitry to extract useful spatial and spectral information from signals originating in a photoreceptor mosaic with trichromatic constituents that vary widely in their relative numbers and local spatial configurations. A critical early transformation applied to cone sign...
Article
Background: Fundamental spatial vision capabilities of visual systems can be characterized by their contrast sensitivity and visual acuity. Objective: Comparison of contrast sensitivity and visual acuity in humans and other animals. Material and methods: An analysis of known contrast sensitivity functions and maximum visual acuity across selec...
Article
Full-text available
Purpose: To determine the effective dynamic range (EDR), retest reliability, and number of discriminable steps (DS) for mesopic and dark-adapted two-color fundus-controlled perimetry (FCP) using the S-MAIA (Scotopic-Macular Integrity Assessment) "micro-perimeter." Methods: In this prospective cross-sectional study, each of the 52 eyes of 52 subj...
Article
The use of adaptive optics in ophthalmoscopy is a breakthrough technological achievement. With AO ophthalmoscopes, the microscopic retinal structure can be visualised non-invasively and on a cellular level, allowing for cellular scale imaging of the retinal nerve fibre layer, the smallest retinal capillaries, rod and cone photoreceptors, and the re...
Article
Full-text available
During the last 25 years ophthalmic imaging has undergone a revolution. This review gives an overview of the possibilities of adaptive optics (AO) for ophthalmic imaging technologies and their development and illustrates that the role of ophthalmic imaging changed from the documentation of obvious abnormalities to the detection of microscopic yet s...
Article
Full-text available
Even during fixation, our eyes are constantly in motion, creating an ever-changing signal in each photoreceptor. Neuronal processes can exploit such transient signals to serve spatial vision, but it is not known how our finest visual acuity—one that we use for deciphering small letters or identifying distant faces and objects—is maintained when con...
Article
Purpose: To assess the intrasession test-retest reliability of scotopic cyan and scotopic red fundus-controlled perimetry (FCP) in normal subjects using a modified MAIA "microperimeter" (macular integrity assessment) device. Methods: Forty-seven normal eyes of 30 subjects (aged 33.8 years) underwent duplicate mesopic (achromatic stimuli, 400-800...
Article
Full-text available
Equipping an ophthalmoscope with adaptive optics (AO) offers access to the living human retina with unprecedented spatial resolution. With AO, cellular structures such as the nerve fiber layer, the microvasculature of the smallest retinal capillaries, rod and cone photoreceptors and the mosaic of the retinal pigment epithelium are directly observab...
Chapter
Color pervades our visual sensory world, yet our understanding of the neural basis of color perception, starting with the retina and on through the multiple cortical areas that subserve vision, is still incomplete. The L, M, and S cone photoreceptors, being the cellular entry point for trichromatic vision in humans and primates, have been studied i...
Article
Purpose Optical coherence tomography angiography (OCT‑A) allows for the non-invasive, three-dimensional visualization of retinal and chorioidal vascular structures. In this study, this new imaging modality was evaluated in rats. Methods In vivo imaging in Dark Agouti rats was performed using confocal scanning laser ophthalmoscopy (cSLO) and OCT‑A (...
Article
Purpose: To optimize the perceptibility of Haidinger brushes (HB) and to investigate its association with visual acuity and macular pigment density. Methods: In this prospective cross-sectional study, each subject underwent best-corrected visual acuity (BCVA) testing, funduscopy, and assessment of macular pigment optical density (MPOD) using the...
Article
Background: Optical coherence tomography angiography (OCT-A) is a new diagnostic non-invasive method by which the vascular structures of the retina and choroid can be visualized three-dimensionally without need for using fluorescence dyes. The technology of OCT-A is an advancement of the OCT. By means of more powerful software and hardware used fo...
Article
Full-text available
Purpose: We explored whether fixational movements of the eye in the human visual system might enhance visual acuity, by effectively scanning the retinal image with its sparse receptive fields, rather than taking a static snapshot of the retinal image with a fixed sampling array. Methods: We used an adaptive optics scanning laser ophthalmoscope t...
Article
To determine the light sensitivity of poorly reflective cones observed in retinas of normal subjects, and to establish a relationship between cone reflectivity and perceptual threshold. Five subjects (four male, one female) with normal vision were imaged longitudinally (7-26 imaging sessions, representing 82-896 days) using adaptive optics scanning...
Article
Human color vision is initiated by light capture in the trichromatic cone mosaic and the subsequent comparison of these signals across space by post-receptoral retinal circuitry. To probe this process in vivo on a single-cell scale requires knowledge of the topography of the trichromatic mosaic as well as an ability to drive individual photorecepto...
Article
Full-text available
In humans, experimental access to single sensory receptors is difficult to achieve, yet it is crucial for learning how the signals arising from each receptor are transformed into perception. By combining adaptive optics microstimulation with high-speed eye tracking, we show that retinal function can be probed at the level of the individual cone pho...
Conference Paper
By using adaptive optics imaging and tracking, we demonstrate repeatable color percepts ensuing from the same location in the human retina. Testing vision on such cellular scales will advance understanding of retinal processing and diseases.
Article
Insight into the function of sleep may be gained by studying animals in the ecological context in which sleep evolved. Until recently, technological constraints prevented electroencephalogram (EEG) studies of animals sleeping in the wild. However, the recent development of a small recorder (Neurologger 2) that animals can carry on their head permit...
Article
Full-text available
Barn owls are effective nocturnal predators. We tested their visual performance at low light levels and determined visual acuity and contrast sensitivity of three barn owls by their behavior at stimulus luminances ranging from photopic to fully scotopic levels (23.5 to 1.5 × 10(-6)). Contrast sensitivity and visual acuity decreased only slightly fr...
Conference Paper
Chromatic dispersion is a major obstacle for controlled delivery of multi-wavelength light to the retina. We present a rapid, image-based correction method enabling targeted stimulation of the photoreceptor mosaic with sub-cellular resolution.
Article
Full-text available
A special challenge arises when pursuing multi-wavelength imaging of retinal tissue in vivo, because the eye's optics must be used as the main focusing elements, and they introduce significant chromatic dispersion. Here we present an image-based method to measure and correct for the eye's transverse chromatic aberrations rapidly, non-invasively, an...
Article
In the human fovea, retinal wiring shows low or no neural convergence, such that the excitation of single photoreceptor cells is mapped to the receptive field of single ganglion cells. Outside the fovea, a one-to-one wiring is replaced by a less precise retinotopic mapping and increased convergence. As a result, mismappings between the exact retina...
Article
Transverse chromatic aberration (TCA) is one manifestation of chromatic dispersion of the ocular media, in which the images formed by light of different wavelengths are displaced angularly on the retina. The amount of displacement is a function of two factors, the wavelength difference and the displacement of the chief ray from the achromatic axis....
Article
Full-text available
Barn owls are nocturnal predators which have evolved specific sensory and morphological adaptations to a life in dim light. Here, some of the most fundamental properties of spatial vision in barn owls are reviewed. The eye with its tubular shape is rigidly integrated in the skull so that eye movements are very much restricted. The eyes are oriented...
Article
Full-text available
Visual saliency based on orientation contrast is a perceptual product attributed to the functional organization of the mammalian brain. We examined this visual phenomenon in barn owls by mounting a wireless video microcamera on the owls' heads and confronting them with visual scenes that contained one differently oriented target among similarly ori...
Article
Full-text available
The perception of shape-from-stereo is best characterized by the spatial disparity-contrast sensitivity function (DSF). This is the stereo analogue of the well-known luminance-contrast sensitivity function (CSF). In principle, the DSF and CSF portray a visual system's ability to detect spatial modulation as specified by changes in binocular dispari...
Article
Full-text available
The eyes of barn owls (Tyto alba pratincola) display very little aberrations, and have thus excellent optical quality. In a series of behavioral experiments, we tested whether this presumably beneficial feature is also reflected at a perceptual level in this species. As fundamental indicators for visual performance, the spatial contrast sensitivity...
Article
Full-text available
In certain real-life situations, moiré patterns can enhance the observer's ability to resolve fine spatial detail of solid structures, theoretically to unlimited degrees. An example of such a situation can be seen in traffic signs on the M25 motorway around London. Moreover, owing to the interferential nature of the moiré pattern, its angular physi...
Article
Full-text available
In this study we investigated visual attention properties of freely behaving barn owls, using a miniature wireless camera attached to their heads. The tubular eye structure of barn owls makes them ideal subjects for this research since it limits their eye movements. Video sequences recorded from the owl's point of view capture part of the visual sc...
Article
Full-text available
Die optische Qualität des Schleiereulenauges wurde mit einem Tscherning Aberrometer in vier Tieren (acht Augen) unter physiologischen Sehbedingungen bestimmt. Die Ergebnisse zeigen, dass diese Augen hervorragende Abbildungsleistungen besitzen. Die Wellenfrontfehler höherer Ordnung waren im Mittel dreimal niedriger als dies bei Menschen unter vergle...
Article
Full-text available
Optical quality in barn owl eyes is presented in terms of measuring the ocular wavefront aberrations with a standard Tscherning-type wavefront aberrometer under natural viewing conditions. While accommodative state was uncontrolled, all eyes were focused within 0.4D with respect to the plane of the aberrometer. Total RMS wavefront error was between...
Article
Vernier acuity thresholds were obtained psychophysically in three adult barn owls with vertical bars and sinusoidal gratings. A minimal displacement threshold of 0.58 arcmin was observed with the bar stimulus under binocular viewing conditions. The mean binocular bar threshold was 2.51 arcmin. Bar thresholds were lower than grating thresholds. Mono...

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