Visual Snow Syndrome as a Network Disorder: A Systematic Review

What does visual snow look like? Quantification by matching a simulation

The primary symptom of visual snow syndrome (VSS) is the unremitting perception of small, flickering dots covering the visual field. VSS is a serious but poorly understood condition that can interfere with daily tasks. Several studies have provided qualitative data about the appearance of visual snow, but methods to quantify the symptom are lacking. Here, we developed a task in which participants with VSS adjusted parameters of simulated visual snow on a computer monitor until the simulation matched their internal visual snow. On each trial, participants (n = 31 with VSS) modified the size, density, update speed, and contrast of the simulation. Participants' settings were highly reliable across trials (intraclass correlation coefficients > 0.89), and they reported that the task was effective at stimulating their visual snow. On average, visual snow was very small (less than 2 arcmin in diameter), updated quickly (mean temporal frequency = 18.2 Hz), had low density (mean snow elements vs. background = 2.87%), and had low contrast (average root mean square contrast = 2.56%). Our task provided a quantitative assessment of visual snow percepts, which may help individuals with VSS communicate their experience to others, facilitate assessment of treatment efficacy, and further our understanding of the trajectory of symptoms, as well as the neural origins of VSS.

Visual snow syndrome: recent advances in understanding the pathophysiology and potential treatment approaches

PURPOSE OF REVIEW

Visual snow syndrome (VSS) is a disorder characterized by persistent visual disturbances, including the visual snow phenomenon, palinopsia, heightened perception of entoptic phenomena, impaired night vision, and photophobia. The purpose of this review is to provide an update on recent findings over the past 18 months in VSS research and to summarize the current state of treatment approaches.

RECENT FINDINGS

Electrophysiological studies have revealed cortical hyperresponsivity in visual brain areas, imaging studies demonstrated microstructural and functional connectivity alterations in multiple cortical and thalamic regions and investigated glutamatergic and serotoninergic neurotransmission. These findings suggest that VSS might be a network disorder.Only few treatment studies are currently available demonstrating limited response to medication and even worsening or triggering of visual symptoms by certain antidepressants. Promising nonpharmacological treatments include mindfulness-based cognitive therapy, the use of chromatic filters, and research on visual noise adaption and neuro-optometric visual rehabilitation therapy (NORT). However, the level of evidence is still low and further research is needed including larger trials and involving objective measures of individual dysfunction.

SUMMARY

Although there has been recent progress, we still have not fully understood the nature of VSS. Further research is needed on a clinical and pathophysiological level to successfully treat the condition.

Visual Snow Syndrome in Patient with Migraine: Case Report and Literature Review

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.

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.

Symptomatic visual snow in acute ischemic stroke: A case series

Visual snow is the main symptom of visual snow syndrome, a disorder of predominantly visual disturbances initially described in patients without abnormalities on ancillary investigations. We present a case series of patients with visual snow in the setting of acute ischemic stroke. The first and second patient reported previous episodic visual snow with migraine attacks. The third patient experienced visual snow for the first time during the ischemic stroke. In the first patient, the ischemic stroke affected the right and left precuneus and the right lingual gyrus. In the second patient, the ischemic stroke was located in the left lingual gyrus, parts of the left fusiform and parahippocampal gyrus, left dorso-lateral thalamus, and left cerebellar hemisphere. In the third patient, occipital pole, trunk of the corpus callosum on the right, right paramedian pons, right cerebellar hemisphere, and vermis were affected. Our case series indicates that the symptom visual snow can be caused by vascular lesions in areas of visual processing. Because patients did not meet criteria for visual snow syndrome, dysfunction in the affected areas might only explain part of the complex pathophysiology of visual snow syndrome.

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

PURPOSE

Visual snow syndrome (VSS) is a recently recognized chronic neurologic condition characterized by the constant perceiving of tiny flickering dots throughout the entire visual field. Metabolic overactivity and grey matter volume increase in the lingual gyrus has been reported. We investigated this by ¹⁸F-FDG PET/MR in comparison to healthy controls. Aside from voxel-based characterization, the classification accuracy of volume-of-interest (VOI)-based multimodal assessment was evaluated, also in comparison with visual analysis.

METHODS

Simultaneous ¹⁸F-FDG PET and MR imaging was performed in 7 patients with VSS (24.6 ± 5.7 years; 5 M/2F) and 15 age-matched healthy controls (CON) (28.0 ± 5.3 years; 8 M/7F). SPM12 and voxel-based morphometric analysis was performed. A VOI-based discriminant analysis was performed with relative ¹⁸F-FDG uptake, MR grey matter (GM) volumes and their combination. A visual analysis was done by two blinded experienced readers.

RESULTS

Relative increased hypermetabolism was found in VSS patients in the lingual gyrus and cuneus (p_FWE < 0.05, peak change + 24%), and hypometabolism in the mesiotemporal cortex (p_{height,uncorr} < 0.001, peak change - 14%). VSS patients also had increased GM volume in the limbic system and frontotemporal cortex bilaterally (p_FWE < 0.05), and in the left secondary and associative visual cortex and in the left lingual gyrus (p_{height,uncorr} < 0.001). Discriminant analysis resulted in 100% correct classification accuracy for ¹⁸F-FDG with lingual gyrus, cuneus and lateral occipital lobe (BA 17 and BA 18) as main discriminators. Unimodal MR- and combined ¹⁸F-FDG + MR classification resulted in an accuracy of 91% and 95%, respectively. Visual analysis of ¹⁸F-FDG was highly observer dependent.

CONCLUSION

Patients with VSS have highly significant structural and metabolic abnormalities in the visual and limbic system. VOI-based discriminant analysis of ¹⁸F-FDG PET allows reliable individual classification versus controls, whereas visual analysis of experienced observers was highly variable. Further investigation in larger series, also in comparison to VSS mimicking disorders such as migraine, is warranted.

TRAIL REGISTRATION

Retrospectively registered at clinicaltrials.gov under NCT05569733 on Oct 5, 2022.

The efficacy of neuro-optometric visual rehabilitation therapy in patients with visual snow syndrome

Objective

This study intends to evaluate the feasibility of Neuro-Optometric Rehabilitation Therapy (NORT) to treat Visual Snow Syndrome (VSS). This pilot study utilized the National Eye Institute Visual Function Questionnaire (NEI-VFQ-25) to assess quality of life (QOL) before and after treatment.

Methods

Twenty-one participants were recruited as successive intake patients diagnosed with VSS at the clinics of Dr. Terry Tsang Optometry, Inc and Neuro-Vision Associates of North Texas. Participants completed the NEI Visual Function Questionnaire 25-2000 edition and performed NORT, conducted by a neuro-optometrist or a qualified vision therapist. The NEI-VFQ-25 was administered before, at 6 weeks, and at 12 weeks of NORT to evaluate the effects of treatment on patient QOL.

Results

The participants demonstrated an improvement in QOL composite and subscale scores after 6 and 12 weeks of NORT treatment. The NEI-VFQ-25 composite scores from the pre-test (M = 68, SD = 18) and at 6 weeks of treatment (M = 75, SD = 17) indicate an improvement in QOL [t (20) = 4.0, p = 0.0007]. The NEI-VFQ-25 composite scores from pretest to 12 weeks of treatment showed further improvements. This trend of improvement on NEI-VFQ-25 composite scores continued into the 12th week (M = 77, SD = 17) of treatment [t (20) = 4.5, p = 0.0002]. The subscales of general vision, distance activities, near activities, social functioning, mental health, role difficulties and dependency also showed improvement.

Conclusion

Our results suggest that patients with VSS experience improvement in QOL in as little as 6 weeks, with further improvement by 12 weeks of NORT. This suggests NORT is an effective treatment option for managing the condition and improving QOL in patients with VSS, although a reduction in specific symptoms has yet to be demonstrated. This study provides justification that NORT warrants further investigation on VSS symptom reduction.

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 is probably not mediated by CGRP: A case series

BACKGROUND

Visual snow syndrome is a phenomenon for which no effective treatment is known. It is highly comorbid with migraine, therefore we performed a retrospective chart review of patients with visual snow syndrome treated with a monoclonal antibody against calcitonin gene related peptide or its receptor.

FINDINGS

We enrolled 15 patients with visual snow syndrome who received at least once a monoclonal antibody against calcitonin gene related peptide or its receptor. None of the patients reported relief of visual snow syndrome whereas those patients with comorbid migraine reported a very good efficacy of the antibody against the migraine headache but not against the migraine aura.

CONCLUSION

The data suggest that visual snow syndrome is not mediated by calcitonin gene related peptide in a relevant way and that the calcitonin gene related peptide receptor is not involved in the network underlying the visual snow syndrome.

Case Report: Transformation of Visual Snow Syndrome From Episodic to Chronic Associated With Acute Cerebellar Infarct

Visual snow syndrome is a novel neurological condition characterized by a panfield visual disturbance associated with several additional symptoms. Although it is usually a continuous and primary disorder, cases of intermittent visual snow have been described in the literature, as well as rare secondary forms. This report is the first description of a case of intermittent visual snow syndrome, which transformed into a persistent form following a posterior circulation stroke due to vertebral artery dissection. At 1 and 2 years after experiencing the acute cerebellar infarct, the patient's only neurological sequalae was visual snow. This case provides a description of how visual snow syndrome may be caused by an underlying brain disorder, and highlights the importance of the cerebellum in the pathophysiology of this relatively unknown condition. It further shows evidence of how existing predispositions might be relevant to the development of visual snow, in certain subjects and following specific circumstances.