Not All That Flickers Is Snow

How do I recognise and manage visual snow syndrome?

Visual snow syndrome (VSS) is becoming increasingly recognised by clinicians and self-diagnosed by our patients thanks to online search tools. Previously this phenomenon was overlooked or dismissed leading to increased patient anxiety. Now, however, we need to be careful with that we are not making what would seem to be an easy diagnosis of VSS when actually we are missing any underlying or mimic conditions.

Visual Snow: Updates and Narrative Review

PURPOSE OF REVIEW

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.

RECENT FINDINGS

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.

Case report: Visual snow as the presenting symptom in multiple evanescent white dot syndrome. Two case reports and literature review

Purpose

Multiple evanescent white dot syndrome (MEWDS) usually manifests as photopsia, enlarged blind spots, scotomas, and blurred vision, which can be classified into positive and negative visual phenomena. Visual snow and chromatopsia were rarely reported in these patients. Herein, we described two Chinese female patients with MEWDS who initially presented with visual snow, and one of them also had yellow-tinged vision.

Methods

First, we performed the chart review of two patients. Second, we reviewed the English literature for all cases of MEWDS through PubMed until December 2021, using the terms “MEWDS” or “multiple evanescent white dot syndrome.” We concluded on all the reported patients' demographic features and symptoms. The visual acuity of patients with/without positive or negative visual phenomena was compared through one-way ANOVA.

Results

Patient 1: A 27-year-old Chinese woman experienced continuous visual snow and yellow-tinged vision in the right eye for a week. She noticed tiny white and black dots involving the entire visual field and shimmering light inferiorly. Patient 2: A 22-year-old Chinese woman complained of a gray area with continuous visual snow in the temporal visual field of the left eye for 5 days. The ocular examinations, including fundus autofluorescence (FAF), optical coherence tomography (OCT), and indocyanine green angiography (ICGA), confirmed the diagnosis of MEWDS. Their symptoms resolved spontaneously without treatment. We found 60 MEWDS case reports (147 cases) in PubMed. The mean age was 31.2 years old. The mean LogMAR best-corrected visual acuity was 0.35 ± 0.39 at the first visit and 0.01 ± 0.16 at the last visit. The most common symptoms included blurred vision (72.8%), enlarged blind spot (42.2%), photopsia (37.4%), and scotoma (33.3%). We found the patients with only positive visual phenomena had significantly worse visual acuity at the first and last visit than patients with only negative visual phenomena (p = 0.008) or the patients with both positive and negative visual phenomena (p = 0.026). Four cases similar to visual snow were discovered. Compared to the MEWDS patients without visual snow, the patients with visual snow tend to have a larger proportion of females (p = 0.005) and a better visual acuity at the first visit (p = 0.007).

Conclusion

Herein, we expand upon the clinical manifestations of MEWDS with visual snow, and the symptoms attributable to visual snow could precede the onset of MEWDS. Neurologists and ophthalmologists should carefully rule out occult chorioretinopathy before diagnosing visual snow syndrome.

Visual Snow Syndrome as a Network Disorder: A Systematic Review

Aim: By reviewing the existing clinical studies about visual snow (VS) as a symptom or as part of visual snow syndrome (VSS), we aim at improving our understanding of VSS being a network disorder. Background: Patients with VSS suffer from a continuous visual disturbance resembling the view of a badly tuned analog television (i.e., VS) and other visual, as well as non-visual symptoms. These symptoms can persist over years and often strongly impact the quality of life. The exact prevalence is still unknown, but up to 2.2% of the population could be affected. Presently, there is no established treatment, and the underlying pathophysiology is unknown. In recent years, there have been several approaches to identify the brain areas involved and their interplay to explain the complex presentation. Methods: We collected the clinical and paraclinical evidence from the currently published original studies on VS and its syndrome by searching PubMed and Google Scholar for the term visual snow. We included original studies in English or German and excluded all reviews, case reports that did not add new information to the topic of this review, and articles that were not retrievable in PubMed or Google Scholar. We grouped the studies according to the methods that were used. Results: Fifty-three studies were found for this review. In VSS, the clinical spectrum includes additional visual disturbances such as excessive floaters, palinopsia, nyctalopia, photophobia, and entoptic phenomena. There is also an association with other perceptual and affective disorders as well as cognitive symptoms. The studies that have been included in this review demonstrate structural, functional, and metabolic alterations in the primary and/or secondary visual areas of the brain. Beyond that, results indicate a disruption in the pre-cortical visual pathways and large-scale networks including the default mode network and the salience network. Discussion: The combination of the clinical picture and widespread functional and structural alterations in visual and extra-visual areas indicates that the VSS is a network disorder. The involvement of pre-cortical visual structures and attentional networks might result in an impairment of "filtering" and prioritizing stimuli as top-down process with subsequent excessive activation of the visual cortices when exposed to irrelevant external and internal stimuli. Limitations of the existing literature are that not all authors used the ICHD-3 definition of the VSS. Some were referring to the symptom VS, and in many cases, the control groups were not matched for migraine or migraine aura.

Two hundred and forty-eight cases of visual snow: A review of potential inciting events and contributing comorbidities

OBJECTIVE

To review characteristics and outcomes of all cases of visual snow seen at our institution, with attention to possible triggering events or comorbidities.

METHODS

This is a retrospective case series of patients seen at our tertiary care center from January 1994 to January 2020. Charts were reviewed if they contained the term "visual snow".

RESULTS

Of the 449 charts reviewed, 248 patients described seeing visual snow in part or all of their vision. Thirty-eight reported transient visual snow as their typical migraine aura. Of the remaining 210 patients, 89 were reported to have either an inciting event or contributing comorbidity for their visual snow symptoms, including: Post-concussion (n = 15), dramatic change in migraine or aura (n = 14), post-infection (n = 13), hallucinogen persisting perception disorder (n = 10), ocular abnormalities (n = 7), idiopathic intracranial hypertension (n = 4), neoplastic (n = 1), and posterior cortical atrophy (n = 1). Some patients had partial improvement with benzodiazepines (n = 6), lamotrigine (n = 5), topiramate (n = 3) and acetazolamide (n = 3). Presenting characteristics were similar, but patients with visual snow attributed to an inciting event or contributing comorbidity were more likely to have some improvement in their symptoms by last follow-up compared to spontaneous visual snow (p < .001).

CONCLUSIONS

Though most cases of visual snow are spontaneous, potential secondary causes should be recognized by clinicians. Patients who develop visual snow after an inciting event or related to an underlying comorbidity may have a better prognosis than those in whom it develops spontaneously. In select cases, treatment of the suspected underlying cause may significantly alleviate the otherwise typical intractable visual disturbances associated with visual snow.

Visual Snow-Like Symptoms and Posterior Uveitis following COVID-19 Infection

Visual snow (VS) is a neurologic condition consisting of a constant positive visual disturbance described as "static" with diagnosis requiring exclusion of competing neurologic and ophthalmologic disorders. The authors describe the first case of visual snow-like symptoms in a patient following coronavirus disease 2019 (COVID-19) infection. He was found to have a transient subtle mild inflammatory reaction in the vitreous and optic nerve edema which resolved, but the VS persisted. Our findings suggest that COVID-19 may precipitate a transient autoimmune response in some patients with resultant ocular inflammation as well as long-term symptoms of VS. This has potential implications for the understanding and treatment of complications related to COVID-19 and in VS.

Not All Cases of Visual Snows are Benign: Mimics of Visual Snow Syndrome

Visual snow syndrome (VSS) is a clinical disorder characterized by pan-field visual disturbance. It is a diagnosis of exclusion since its pathophysiology remains unknown. Excluding other mimics is of great significance since some serious pathologies can have secondary visual snow (VS) as an initial presentation. Delayed or incorrect diagnosis of these VSS mimics may lead to permanent vision loss or even death. The purpose of this review is to help physicians distinguish VSS mimics promptly to avoid bad outcomes. The authors performed a PubMed literature search of articles, case reports, and reviews describing VS symptoms in patients with underlying diseases other than VSS. The red flags of secondary VS symptoms were highlighted, such as new-onset or intermittent VS, unilateral or quadrant VS, and accompanied ocular or neurological deficits. There are four main categories of VSS mimics, ie, including neurological disorders, ocular pathologies, drug-related VS, and other systemic diseases. The physicians could largely exclude most etiologies based on history taking, ophthalmologic and neurologic examinations, and neuroimaging. Further research in VS should carefully define and unify the inclusion and exclusion criteria of this disorder and investigate these secondary VS conditions and their pathogenesis.