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Eye Microcirculation
Published in John H. Barker, Gary L. Anderson, Michael D. Menger, Clinically Applied Microcirculation Research, 2019
There are several entoptic phenomena permitting the visualization of capillary flow.43 The blue-light entoptic phenomenon has been utilized most widely in clinical settings.44 The (cooperative) subject views an evenly blue illuminated screen with one eye. The flying spots presumably originate from relatively slow passage of leukocytes through the perimacular capillary network, causing a gap in the erythrocyte column. The observed field of moving dots is matched subjectively to a simulation on a computer screen presented to the other eye. It is the task of the subject in the two views to match the number of flying spots, their velocity, and (in very cooperative persons) also the pulsating velocity. The method has the drawback of being subjective and presumably measures the velocity of leukocytes that could be different from the erythrocyte velocity. The observed velocities are in the range of 0 to 2 mm/s.
Rehabilitation and management of visual dysfunction following traumatic brain injury
Published in Mark J. Ashley, David A. Hovda, Traumatic Brain Injury, 2017
Fixation, or the act of holding gaze steady on a target, was once thought to be a function of the pursuit system at zero velocity. This may be why fixation, itself, is seldom evaluated except in relation to strabismic amblyopia. However, recent evidence implicates an independent visual fixation system, perhaps located in the parietal lobe.107 Disturbances in fixation may be considered in terms of inability to sustain fixation as well as inability to fixate centrically and steadily. The former can be easily observed by having the patient hold fixation on a target for a minute. The ability to fixate steadily and centrically is only observable with special techniques. The easiest, most objective measure is with a visuoscope or, similarly, an ophthalmoscope with a central target. The examiner looks into the patient’s eye with the scope, which projects a target onto the retina. The anatomy of the posterior pole of the eye and the projected target are viewed simultaneously. The patient is instructed to fixate the target while covering the other eye. The stability of the foveal reflex and centricity with regard to the target are easily observed in this manner. Other methods require reliable subjective feedback. For instance, the Haidinger brush, an entoptic phenomenon that marks the fovea, may be elicited with an instrument such as the Macular Integrity Tester4 with which the patient fixates a target and reports the location and stability of the Haidinger brush in relation to the fixated target.
Ocular Blood Flow and Metabolism
Published in Neil T. Choplin, Carlo E. Traverso, Atlas of Glaucoma, 2014
Alon Harris, Leslie Abrams Tobe, Brent Siesky
Blue field entopic techniques are founded on the blue field entoptic phenomenon. This phenomenon is based on the observation of leukocytes flowing through the subject’s own retinal macular vasculature. These methods can be used for a noninvasive, subjective evaluation of perimacular hemodynamic parameters but are not often utilized because the technique is based on the assumption that macular capillaries have a fixed diameter while, in reality, large variations between patients exist. Also, data is limited to the perifoveal anatomical region and depends on the patient’s cooperation and perception.
Proceedings of the 44th Annual Upper Midwest Neuro-Ophthalmology Group Meeting
Published in Neuro-Ophthalmology, 2023
Negar Moheb, Adam Baim, Collin McClelland, John. J. Chen
The conference concluded with a presentation by Sophia M. Chung, MD, University of Iowa, that reviewed the manifestations of visual snow and the state of current research on visual snow syndrome. Originating within the lay public as a description for positive visual symptoms, visual snow is often described as flickering dots encompassing the entire visual field. Dr Chung demonstrated several online simulators of visual snow, conveying the variety of symptoms that can fall under this category and providing conference participants with valuable tools for discussing visual snow symptoms to their patients. The talk also described the emergence of diagnostic criteria for visual snow syndrome, where visual snow is accompanied by a combination of illusory palinopsia, enhanced entoptic phenomenon, photophobia, or nyctalopia. Research into the pathophysiology and treatment of visual snow was discussed, highlighting the need for further study of this new diagnostic entity.
Heinrich Müller (1820-1864) and the entoptic discovery of the site in the retina where vision is initiated
Published in Journal of the History of the Neurosciences, 2022
John S. Werner, Iwona Gorczynska, Lothar Spillmann
At the time of Müller’s 1855 paper, it was known that light must be absorbed by a pigment in order to convert electromagnetic energy into neural signals. In the cadaver eye, the photopigment cannot be seen without careful preparation due to bleaching (photo-isomerization). It had generally been thought that transduction must occur in the ganglion cell layer because it is the first retinal layer that is reached by the incident light, as shown in Figure 2.3. Müller correctly deduced from his careful entoptic experiments using the Purkyně tree that this was incorrect and that, instead, vision is initiated in cells we now know to be the photoreceptors located in the back of the retina. The elegance of Müller’s (1855) experiments and analyses prompted us to translate his paper. His scientific approach stands out for his use of perceptual observations to understand anatomical and physiological function, an approach used by other nineteenth-century anatomists and histologists such as Max Schultze, Hermann Munk, and others—a perspective that continues to guide vision science. Müller showed how careful observations (entoptic phenomena) and simple mathematics can be used to make inferences about retinal structures.
Transient vision loss: a neuro-ophthalmic approach to localizing the diagnosis
Published in Expert Review of Ophthalmology, 2018
Helen Chung, Jodie M. Burton, Fiona E. Costello
Patients with ‘visual snow’ often compare their perceptual disturbances to viewing a badly tuned analog television [39]. More specifically, affected individuals describe a multitude of tiny dots in the entire visual field, often flickering between black and white. Symptoms of visual snow tend to be continuous (not transient) and persist whether the eyes are open or closed [39]. Yet, many patients with visual snow report other transient visual symptoms, including: palinopsia, exaggerated entoptic phenomena (floaters, blue field entoptic phenomenon, spontaneous photopsia), photophobia, and nyctalopia (impaired night vision), which may recover acutely, subacutely, or chronically over time [3].