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Causes entoptic phenomena6/23/2023 Instead, the associated symptoms of palinopsia and enhanced entoptic phenomena suggest a problem with visual processing in the supplementary visual cortex. The lack of monocular or homonymous visual field defect makes dysfunction in the anterior visual pathway, optic radiations or primary visual cortex unlikely. The bilaterality, diffuse involvement of the entire visual fields, and the constancy of symptoms support the concept that the pathology is cortical. One hypothesis suggests that VS is caused by dysfunction in the secondary or supplementary visual cortex surrounding the primary cortex. Two main hypotheses have emerged to explain the pathophysiology of VS based on the clinical description and additional symptoms, although neither has been explicitly cited as the sole explanation. However, early neuroimaging studies have helped further our understanding. The neurophysiological mechanism of visual snow is poorly understood and research in this area is in its infancy. Comorbid conditions, such as migraine, tinnitus, and migraine aura may also be seen, and are more common among patients with visual snow syndrome compared to visual snow. Roughly 40% of patients describe having symptoms since childhood, with nearly a quarter reporting sudden onset of symptoms. VS tends to occur in younger patients, with an average age of 29 years. In a subsequent study in 2015, Schankin et al., identified visual snow syndrome as a unique clinical entity distinct from migraine aura and proposed diagnostic criteria (see "Diagnosis" section below). The study also did not find causal relationship between mental illness and VS but did note that anxiety and depression were common long-term comorbidities. Schankin, et al., addressed these common misconceptions in 2014 concluding no associations between illicit drug use and VS. Other early studies suggested VS to be a clinical phenomenon secondary to illicit drug use or mental illness, known as hallucinogen persistent perception disorder. al, in 1995 is generally given credit for the initial series of patients with detailed descriptions of the symptoms of visual snow when it was described as persistent migraine aura. Visual snow (VS) has been given a variety of names, most referring to prolonged or sustained migraine aura dating back to 1982 by Haas. Patients can also experience non-visual symptoms, most commonly, bilateral tinnitus. When accompanied by two of the four additional visual symptoms: palinopsia (persistence of an image after stimulus), enhanced entoptic phenomena (e.g., floaters), photophobia and nyctalopia (poor night vision), the constellation is known as the visual snow syndrome. This symptom often persists even with the eyes closed. The flickering dots resemble 'static' or 'snow' and are interposed between the patient's vision and background. Visual snow is a neurologic condition that manifests with persistent positive visual symptoms consisting of tiny flickering dots covering the entire visual field. When shown an online visual snow simulator, he confirmed his symptoms matched the computer simulation. Given his unremarkable anterior and funduscopic exams, the constancy of the visual phenomena and their diffuse static-like character, his constellation of symptoms were most consistent with visual snow. Magnetic resonance imaging of the brain and orbits with and without contrast was normal. It was normal on the right and showed foveal vitreomacular adhesion and subfoveal drusen on the left. Optical coherence tomography (OCT) of the optic nerve head and retinal nerve fiber layer (RNFL) performed elsewhere were reviewed. Goldmann Visual Field demonstrated constriction of the I1e isopter, but was otherwise full.
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