Visual Snow: Updates on Pathology

Abstract

Purpose of Review Until the last 5 years, there was very little in the literature about the phenomenon now known as visual snow syndrome. This review will examine the current thinking on the pathology of visual snow and how that thinking has evolved. Recent Findings While migraine is a common comorbidity to visual snow syndrome, evidence points to these conditions being distinct clinical entities, with some overlapping pathophysiological processes. There is increasing structural and functional evidence that visual snow syndrome is due to a widespread cortical dysfunction. Cortical hyperexcitability coupled with changes in thalamocortical pathways and higher-level salience network controls have all shown differences in patients with visual snow syndrome compared to controls. Summary Further work is needed to clarify the exact mechanisms of visual snow syndrome. Until that time, treatment options will remain limited. Clinicians having a clearer understanding of the basis for visual snow syndrome can appropriately discuss the diagnosis with their patients and steer them towards appropriate management options.

Simultaneous 18F-FDG PET/MR metabolic and structural changes in visual snow syndrome and diagnostic use

“…VSS seems to involve aberrant processing of visual information in the supplementary visual cortex, and there is increasing evidence that VSS involves multiple mechanisms with cortical dysfunction also outside the visual system. Cortical hyperexcitability, due to increased neural contrast gain rather than abnormal neural noise [ 17 ], changes in specific visual streams, altered thalamocortical pathways and dysfunction of higher-level salience network controls have been suggested [ 18 ]. Interestingly, tinnitus, considered the auditory analogue to visual snow, is also highly prevalent in VSS, which suggests a common pathway [ 19 ].…”

Traumatic brain injury: Mechanisms, manifestations, and visual sequelae

“…Visual snow syndrome (VSS), a rare condition characterized by the appearance of pixelated flickering dots in one plane in front of and throughout a visual field, may be incited by mTBI (Ciuffreda et al, 2021;Hang et al, 2021;Mehta et al, 2021;Werner and Gustafson, 2022). The pathophysiology of VSS is not wellunderstood, there is no effective treatment and it tends to persist over time (Fraser, 2022).…”

Should Visual Snow and Visual Snow Syndrome Be Evaluated Outside of Standard In-clinic Ophthalmologic Testing?

“…Autoimmune retinopathy is characterized by circulating antiretinal antibodies that cause photoreceptor dysfunction. Patients present with photophobia and positive visual scintillations that are often described as gold or silver shimmering in the visual periphery (7). The shimmering is most noticeable in the dark and persists with the eyes closed.…”

“…Thus, perhaps, explaining the association of VSS with migraine aura and tinnitus. However, recent data indicate that the most likely pathophysiology of VS is a combination of peripheral, thalamic, and cortical dysfunction (7).…”

“…Fraser makes some excellent points, and we agree that the cases of patients with secondary VS and VSS should be evaluated beyond the usual testing obtained in the clinic if there is any indication of disorders reported that can mimic VS such as rod-cone dystrophy and idiopathic intracranial hypertension (IIH) as noted above by Yoo et al ( 4), Creutzfeldt-Jakob disease (12), paraneoplastic syndromes such as glycine receptor antibody syndrome (8), head trauma (immediate or delayed onset) (13), and hallucinogen-persisting disorder (7,9,29). Basically, any neurological condition that affects the occipital lobe may trigger or mimic VS including epilepsy, posterior cortical atrophy, stroke (10), and positive spontaneous visual phenomena from visual deprivation (Charles Bonnet syndrome) from ocular, optic nerve, and tract, chiasmal, or postchasmal etiologies (7,30,31). In addition, retinal diseases such as cancer-associated or melanoma-associated retinopathy (32), retinitis pigmentosa, uveitis, age-related macular degeneration, central serous retinopathy, multifocal choroiditis with macular involvement, birdshot chorioretinopathy, and optic atrophy have been associated with VS (10).…”