Since the first description of visual snow syndrome (VSS) in 1995, there has been increasing interest particularly within the past 5-10 years in phenotyping the condition and differentiating it from conditions such as migraine with aura and hallucinogen persisting perception disorder. Structural and functional neuroimaging has provided valuable insights in this regard, yielding functional networks and anatomical regions of interest, of which the right lingual gyrus is of particular note. Various modalities, including functional magnetic resonance imaging (fMRI), positron emission tomography (PET), and single photon emission computed tomography (SPECT), have all been studied in patients with visual snow. In this article, we conduct a comprehensive literature review of neuroimaging in VSS.

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Visual snow syndrome (VSS) is a rarely diagnosed neurological phenomenon. It is a visual disorder characterised by the presence of numerous white, black, or translucent dots in the visual field, resembling the \'snow\' of an analogue TV set experiencing reception interference. According to The International Classification of Headache Disorders, 3rd edition, visual snow is defined as a pattern of continuous small dots across the visual field lasting >3 months and accompanied by at least two of the following four additional symptoms: palinopsia, increased entoptic phenomena, photophobia, and nyctalopia. These complaints are not consistent with a typical migraine with visual aura and cannot be better explained by another disorder. The authors present the case of a 39-year-old woman who was diagnosed with VSS. The symptoms appeared after a migraine attack and had not alleviated. The patient reported a sensation of constant \'TV screen snow\'. A neurological examination found no signs of focal damage to the nervous system. The results of the ophthalmological examination, MRI of the brain with contrast, MRI of the eye sockets, and EEG were normal. VSS is a phenomenon that is still not fully understood, different from migraine aura and associated with a number of additional symptoms. VSS is very difficult to treat. In this case, a lot of drugs were used without improvement. Further research must be conducted to determine the best treatment options for these patients.

OBJECTIVE: Migraine is the comorbidity most frequently associated with visual snow syndrome (VSS), but the prevalence of VSS in patients with migraine (PWM) has not been studied. Our objective was to evaluate the frequency of VSS in PWM and to analyze if symptoms of VSS happened in a permanent or episodic manner (eVSS) in this population.
METHODS: We conducted a multicenter observational cross-sectional study. PWM was recruited from headache units, and a survey about the presence of visual snow symptoms was administered. The frequency and characteristics of patients that met current VSS criteria were analyzed. Demographic and clinical features of patients with VSS, eVSS, and PWM with no visual snow were compared.
RESULTS: A total of 217 PWM were included. Seventeen patients (7.8%) met the VSS criteria. VSS patients had visual aura more frequently (58.8% vs. 31%; p = 0.019) and a higher MIDAS score (96.6 vs. 47.7; p = 0.014). Fifty-eight PWM (26.7%) showed visual snow and associated features in an episodic way and were classified as eVSS. Patients with VSS showed a tendency towards a higher frequency of visual symptoms than patients with eVSS (p > 0.05). No statistically significant differences in sociodemographic characteristics and comorbid conditions were found between VSS and eVSS.
CONCLUSIONS: The prevalence of VSS in PWM may be higher than that described for the general population. Some PWM may present similar visual symptoms to patients with VSS but in an episodic manner. Our study reinforces the observation that the clinical spectrum of visual snow is likely to be broader than previously described.

In neurology practice, it is common to encounter a variety of visual complaints. Historically, in the absence of known ocular pathology, epilepsy, or insult to the central nervous system, positive symptoms were assumed to be migrainous in origin. This assumption was sometimes made even in the absence of a history of migraine. In the past decade, there has been considerable effort to better delineate and study nonmigrainous visual phenomena, with the most extensive focus on a newly defined syndrome, visual snow syndrome (VSS). The heightened awareness of visual snow as a symptom and syndrome has greatly enhanced the understanding of this visual phenomenon; however, in the last few years, there has been an almost pendulous swing in clinic, with patients now being given the diagnosis of VSS for any dots or flickering they may have in their vision. To avoid clinical misdiagnosis, it is critical that we expand our understanding not just of VSS but also of underlying pathologies that may present similarly. This chapter will review classical migraine aura, persistent migraine aura, visual snow and a number of positive and negative visual complaints that are on the differential when seeing patients with suspected aura or visual snow. This is followed by an in-depth discussion on the current understanding of the presenting symptoms, pathophysiology, evaluation and management of VSS. We also outline secondary causes of visual snow.

OBJECTIVE: Visual snow (VS) involves visualization of innumerable dots throughout the visual field, sometimes resembling \"TV static.\" Patients who experience this symptom may also have additional visual symptoms (e.g., photophobia, palinopsia, floaters, and nyctalopia) with a pattern now defined as visual snow syndrome (VSS). This manuscript describes both VS and VSS in detail and provides an updated review on the clinical features, pathophysiology, and optimal management strategies for these symptoms.
RESULTS: VS/VSS may be primary or secondary to a variety of etiologies, including ophthalmologic or brain disorders, systemic disease, and medication/hallucinogen exposure. Evaluation involves ruling out secondary causes and mimics of VS. Increasing evidence suggests that VSS is a widespread process extending beyond the visual system. Pathophysiology may involve cortical hyperexcitability or dysfunctional connectivity of thalamocortical or attention/salience networks. VSS is typically a benign, non-progressive syndrome and can be managed with non-medicine strategies. Though no medication provides complete relief, some may provide partial improvement in severity of VS.

OBJECTIVE: Visual snow syndrome (VSS) is a complex neurological condition presenting with an array of sensory, motor, and perceptual dysfunctions and related visual and non-visual symptoms. Recent laboratory studies have found subtle, basic, saccadic-based abnormalities in this population. The objective of the present investigation was to determine if saccadic-related problems could be confirmed and extended using three common clinical reading-related eye movement tests having well-developed protocols and normative databases.
METHODS: This was a retrospective analysis of 32 patients (ages 16-56 years) diagnosed with VSS in the first author\'s optometric practice. There was a battery of three reading-related tests: the Visagraph Reading Eye Movement Test, the Developmental Eye Movement (DEM) Test, and the RightEye Dynamic Vision Assessment Test, all performed using their standard documented protocols and large normative databases.
RESULTS: A high frequency of oculomotor deficits was found with all three tests. The greatest percentage was revealed with the Visagraph (56%) and the least with the RightEye (23%). A total of 77% of patients failed at least one of the three tests.
CONCLUSIONS: The present findings confirm and extend earlier investigations revealing a high frequency of saccadic-based oculomotor problems in the VSS population, now including reading-related tasks. This is consistent with the more general oculomotor/motor problems found in these individuals.

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BACKGROUND: Visual snow syndrome (VSS) is a central nervous system disorder that consists of the constant perception of small black and white dots throughout the entire visual field.
METHODS: VSS can present from infancy to old age, with greater prevalence in the young population, and shows no difference between sexes. The diagnostic criteria include the presence of visual snow and such other visual phenomena as palinopsia, photophobia, nyctalopia, and other persistent visual phenomena. The pathophysiology of VSS is unknown, but hyperexcitability of the visual cortex and a dysfunction in higher-order visual processing are postulated as potential mechanisms. The prevalence of migraine among patients with VSS is high, compared to the general population, and symptoms are more severe in patients presenting both conditions. No effective treatment is available, but the drug with the best results is lamotrigine, which is recommended only in selected cases with severe functional limitation.
CONCLUSIONS: VSS is a little-known and underdiagnosed entity, but the increasing number of studies in recent years has made it possible to establish diagnostic criteria and begin studying its pathophysiology. This entity is closely related to migraine, with overlapping symptoms and probably shared pathophysiological mechanisms.