Visual Snow Syndrome: Proposed Criteria, Clinical Implications, and Pathophysiology

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 and its relationship with migraine

INTRODUCTION

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.

DEVELOPMENT

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.

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.

Understanding visual snow syndrome: A retrospective study from a tertiary eye care center

PURPOSE

Visual snow syndrome is a debilitating neurological condition. A comprehensive eye examination may not detect any abnormalities in this condition. Presently the condition is recognized only through the history elicited. Hence, it becomes important to understand the presenting complaints and profile of these patients. A retrospective study at a tertiary eye care center was undertaken to achieve this goal.

METHODS

Electronic medical records of patients presenting to a Binocular Vision and Orthoptics clinic were reviewed. Records of the patients containing keywords such as "light sensitivity, shadowing, visual snow, multiple images, and night vision" were retrieved and inspected. Those matching the diagnostic criteria of visual snow syndrome were included in the study.

RESULTS

A total of 33 patients (average age ± standard deviation: 29.7 ± 9.8 years) were identified. Majority of the patients were males (69%). All the patients had logMAR visual acuity 0 or better in each eye. The most prominent (84.4%) presenting symptom was palinopsia (or afterimage or trailing). About 34.4% complained of floaters (including snow-like appearance). More than half (54.6%) of the patients also had binocular dysfunction.

CONCLUSION

Visual snow syndrome is a relatively new condition on the rise, with unclear pathology. The symptoms of this condition can easily be confused with regular floaters or black spots seen in vitreous and retinal pathologies. In the absence of such pathology, an elaborate history should be elicited, and the distress of the patient should be acknowledged. The patient should also be reassured that this is not a blinding condition.

Visual snow syndrome and migraine: a review

Visual snow syndrome is a neurological condition characterized by ongoing prominent phenomena described consistently as tiny dots moving across the entire visual field, often associated with complex visual symptoms. These can take the form of afterimages, entoptic phenomena, nyctalopia and light sensitivity. Although some of these symptoms can be benign, they can nonetheless become significantly impactful for many who experience them, particularly in cases that have a sudden and abrupt start. As visual snow syndrome becomes increasingly recognized in clinical practice we begin to learn about its typical presentation and underlying pathophysiology. Treatment of visual snow, however, still proves quite challenging, and efforts need to be focused on unravelling the biological mechanisms of the syndrome. This endeavour has characterized the most recent research on visual snow, mostly involving neuroimaging, neurophysiological and neurobehavioral studies aimed at understanding its underlying neural signature. Another important aspect of the syndrome, which will likely prove critical in deepening our understanding of visual snow, is represented by the intricate biological and historical connexion with migraine. This narrative review focused on visual snow syndrome will explore its clinical, pathophysiological and treatment aspects in detail.

Visual Snow: A Review on Pathophysiology and Treatment

OBJECTIVE

Visual snow (VS) is a rare clinical entity in neuro-ophthalmology. It is described as the presence of flickering dots affecting the whole visual field, often compared by patients to snow or pixelated television static. Importantly, it can be an alarming symptom for many patients, lowering their quality of life. Our purpose is to increase awareness of this disease, because many healthcare professionals have difficulty identifying symptoms as the nature of the condition is subjective. In this review, we aimed to describe the updates in the etiology and treatment of visual snow. We searched for articles in English, presenting original data and published after December 2019. Different studies show inconsistent data. Neuroimaging studies found, among other things, hypermetabolism of the lingual gyrus, increased gray matter in different brain areas, and altered connectivity in visual pathways. However, these findings were not present in all patients. According to the literature, among the most effective drugs is lamotrigine. Unfortunately, it also carries a risk of worsening the symptoms. It is crucial to remember that VS can be worsened or induced by alcohol, recreational drugs, and certain medication. In terms of treatment, nonpharmacological approaches such as color filters and repetitive Transcranial Magnetic Stimulation were also used.

INTERPRETATION

Further studies are needed to understand the nature of VS fully. Even though the pathophysiology and effective treatment of the condition remains unknown, expanding the knowledge about visual snow can impact the comfort of patients.

Analysis of Retinal Structure and Electrophysiological Function in Visual Snow Syndrome: An Exploratory Case Series

BACKGROUND

Visual snow (VS) is a rare but distressing phenomenon of persistent granular or pixelated visual distortions that may occur in isolation or as a component of visual snow syndrome (VSS). The current understanding of VS pathogenesis, including the role of retinal involvement structurally and functionally, is limited. The objective of this study is to investigate retinal structural and electrophysiological abnormalities in VS.

METHODS

This retrospective case series included 8 subjects (7 with VSS and 1 with isolated VS). Patients with other ocular and neurologic diseases were excluded. Data were assessed from automated perimetry, optical coherence tomography (OCT), visual evoked potential (VEP), and full-field electroretinography (ffERG) testing. The VEP and ffERG data of visual snow subjects were compared with age- and sex-matched control subjects for statistical significance.

RESULTS

The mean age of the cohort was 29.4 years (SD = ±5.3) with 50% gender split. The mean age of VS onset was 24.2 years (SD = ±3.8). All subjects had normal visual acuity, color vision, brain MRI, automated perimetry, OCT parameters (peripapillary retinal nerve fiber layer and macular ganglion cell layer thickness), and P100 and N135 wave pattern on VEP. Compared with controls, VS subjects had a greater mean b-wave amplitude in response to light-adapted 3.0 stimuli ( t test; P = 0.035 right eye and P = 0.072 left eye), greater mean light-adapted 3.0 flicker amplitude ( t test; P = 0.028 right eye P = 0.166 left eye) and greater b-wave amplitude in response to dark-adapted 10.0 stimuli ( t test; P = 0.102 right eye; P = 0.017 left eye) on ERG.

CONCLUSIONS

Patients with VS and VSS have normal retinal structure, but abnormal electrophysiology compared with control subjects. The increased b-wave and flicker amplitudes observed with ffERG suggest increased responsiveness of the rod and cone photoreceptors and may contribute to VS pathophysiology.

Visual Disturbances Spectrum in Pediatric Migraine

Migraine is a complex neurological disorder with partially unknown pathophysiological mechanisms. The prevalence in childhood ranges from 7.7% to 17.8%, thus representing the most frequent primary headache. In half of the cases, migraine is accompanied or preceded by various neurological disturbances, among which the visual aura is the best known. In literature, other conditions, such as Alice in Wonderland Syndrome and Visual Snow syndrome, are characterized by visual manifestations and are often associated with migraine. The aim of this narrative review is to describe the spectrum of visual disturbances in pediatric migraine and their pathophysiological mechanisms.

Differential Diagnosis of Visual Phenomena Associated with Migraine: Spotlight on Aura and Visual Snow Syndrome

Migraine is a severe and common primary headache disorder, characterized by pain as well as a plethora of non-painful symptoms. Among these, visual phenomena have long been known to be associated with migraine, to the point where they can constitute a hallmark of the disease itself. In this review we focus on two key visual disorders that are directly or indirectly connected to migraine: visual aura and visual snow syndrome (VSS). Visual aura is characterized by the transient presence of positive and negative visual symptoms, before, during or outside of a migraine attack. VSS is a novel stand-alone phenomenon which has been shown to be comorbid with migraine. We discuss key clinical features of the two disorders, including pathophysiological mechanisms, their differential diagnoses and best treatment practices. Our aim is to provide an aid for clinicians and researchers in recognizing these common visual phenomena, which can even appear simultaneously in patients with an underlying migraine biology.

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.

Visual snow: A systematic review and a case series

BACKGROUND

Visual Snow Syndrome is a recently recognized neurological condition presenting, continuous, tiny dots across the entire visual field, accompanied by nyctalopia, photophobia and palinopsia that persist for months. It may be part of migraine aura spectrum, yet its definition is still questionable. Diagnostic criteria for Visual Snow Syndrome are included in the supplemental material of ICHD-3. We aimed to summarize recent data to improve the understanding of Visual Snow Syndrome.

METHODS

After presenting four new cases, we conducted a PRISMA systematic search in PubMed/MEDLINE and Embase databases using the keyword "visual snow" with specific inclusion and exclusion criteria.

RESULTS

From the 855 articles identified 30 were included for the qualitative analysis. These reports covered five aspects related to Visual Snow Syndrome: epidemiology, clinical features, comorbidities, pathophysiology, and treatment. We found limited data concerning Visual Snow Syndrome's epidemiology (one study). Clinical presentation (22 articles) and the comorbidities (migraine with aura and tinnitus most often, five reports) are described in detail. The pathophysiology of Visual Snow Syndrome is only approached with hypotheses, but several neuroimaging studies have been identified (seven articles). Treatment is based on single case reports only.

CONCLUSION

Data for Visual Snow Syndrome are few and not strong enough to support Visual Snow Syndrome as a medical identity. Further investigation is needed.

Visual snow syndrome and the emperor’s new clothes

This scientific commentary refers to ‘Microstructure in patients with visual snow syndrome: an ultra-high field morphological and quantitative MRI study’, by Strik et al. (https://doi.org/10.1093/braincomms/fcac164)

Microstructure in patients with visual snow syndrome: an ultra-high field morphological and quantitative MRI study

Visual snow syndrome is a neurological condition characterized by continuous visual disturbance and a range of non-visual symptoms, including tinnitus and migraine. Little is known about the pathological mechanisms underlying visual snow syndrome. Here, we assessed brain morphometry and microstructure in visual snow syndrome patients using high-resolution structural and quantitative MRI. Forty visual snow syndrome patients (22 with migraine) and 43 controls underwent 7-Tesla MRI (MP2RAGE, 0.75 mm isotropic resolution). Volumetric and quantitative T1 values were extracted for white and grey matter regions and compared between groups. Where regions were significantly different between groups (false discovery rate corrected for multiple comparisons), post hoc comparisons were examined between patients with and without migraine. For visual snow syndrome patients, significant MRI variables were correlated with clinical severity (number of visual symptoms, perceived visual snow intensity, disruptiveness, fatigue and quality of life) and psychiatric symptoms prevalent in visual snow syndrome (depression, anxiety and depersonalization). Finally, cortical regions and individual thalamic nuclei were studied. Compared with controls, visual snow syndrome patients demonstrated a trend towards larger brain and white matter volumes and significantly lower T1 values for the entire cortex (P < 0.001), thalamus (P = 0.001) and pallidum (P = 0.001). For the patient group, thalamic T1 correlated with number of visual symptoms (P = 0.019, r = 0.390) and perceived disruptiveness of visual snow (P = 0.010, r = 0.424). These correlations did not survive multiple comparison corrections. As for specificity in visual snow syndrome group, T1 changes were most evident in caudal regions (occipital cortices) followed by parietal, temporal and prefrontal cortices. T1 values differed between groups for most individual thalamic nuclei. No differences were revealed between patients with and without migraine. In visual snow syndrome patients, we observed no changes in morphometry, instead widespread changes in grey matter microstructure, which followed a caudal-rostral pattern and affected the occipital cortices most profoundly. Migraine did not appear to independently affect these changes. Lower T1 values may potentially result from higher neurite density, myelination or increased iron levels in the visual snow syndrome brain. Further investigation of these changes may enhance our understanding of the pathogenesis of visual snow syndrome, ultimately leading to new treatment strategies.

Visual Snow: Updates on Pathology

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.

Case Report: Visual Snow Syndrome following Repetitive Mild Traumatic Brain Injury

SIGNIFICANCE

Visual snow syndrome is a recently recognized condition with its own diagnostic criteria, evolving pathophysiologic research, and potential treatment options.

PURPOSE

This report documents a rare, but likely underdiagnosed condition called visual snow syndrome. A review of the current literature on pathophysiology and treatments is discussed.

CASE REPORT

A 40-year-old white male started experiencing symptoms of constant pulsating pixels throughout his entire visual field approximately 3 weeks after a series of mild concussions. Additionally, he experienced a persistence of images and photosensitivity. The patient had normal eye exams, visual fields and retinal imaging. Brain magnetic resonance imaging, magnetic resonance angiography, electroencephalography, and cerebrospinal fluid analysis were unremarkable. A positron emission tomography scan demonstrated hypometabolism in the posterior parietal lobes and left posterior cingulate gyrus. Pharmacological treatment with anti-epileptic and migraine medications were unsuccessful. Tinted lenses were essentially ineffective with a 10% reduction in symptoms reported with the use of a custom blue tinted lens. Vision rehabilitation aids with optical character recognition were utilized for prolonged reading needs.

CONCLUSIONS

Although rare, visual snow syndrome should be considered in all patients reporting continuous pixelations in their vision for over 3 months, especially when accompanied by at least two of the following: photosensitivity, palinopsia, enhanced entopic phenomena, or nyctalopia. The pathophysiology is still unclear at this point with evidence suggesting a link to the secondary visual cortex, specifically the lingual gyrus. More studies are needed to determine the exact cause, especially studies that separate visual snow syndrome patients with and without comorbid migraine. Because the pathophysiology is unclear, the treatment course is also unclear. Anecdotal evidence may suggest that tinted lenses may be of some value.

Onset of Visual Snow Syndrome After the First Migraine Episode in a Pediatric Patient: A Case Report and Review of Literature

INTRODUCTION

Visual snow syndrome (VSS) is a neurological disorder characterized by persistent positive visual disturbances. VSS is known to be a rare condition; however, it is becoming increasingly recognized by neurologists and neuroophthalmologists. Despite this, it is not commonly described in pediatric patients.

METHODS

We describe a pediatric girl with onset of persistent visual phenomena at age 13 years, which she described as "TV static," with associated afterimages, photopsia, nyctalopia, and photophobia. These visual disturbances have persisted for two years.

RESULTS

The patient's MRI revealed approximately 15 T2/fluid-attenuated inversion recovery hyperintensities in keeping with changes secondary to migraine. The ophthalmologic examination did not reveal an underlying cause. The patient's visual symptoms have been resistant to medications.

CONCLUSION

VSS is a recently described syndrome that is debilitating to patients. Further case descriptions, characterization of presentation, and management of patients with VSS, specifically in pediatric cases, are required.

Rare Co-Occurrence of Visual Snow in a Female Carrier With RPGRORF15-Associated Retinal Disorder

X-linked retinitis pigmentosa (XLRP), a rare form of retinitis pigmentosa (RP), is predominantly caused by mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene. Affected males often present with severe phenotypes and early disease onset. In contrast, female carriers are usually asymptomatic or show stationary phenotypes. Herein, we reported an 8-year-old female carrier, a daughter of a confirmed RP father with RPGR mutation, with an early onset of progressive cone-rod pattern retinal dystrophy. Additionally, the carrier experienced visual snow-like symptom as long as she recalled. Ophthalmological examination showed the reduction of visual acuity and attenuation of photoreceptor functions since the age of 5 years. Further analysis revealed a heterozygous pathogenic variant of the RPGR gene and a random X-inactivation pattern. Although she harboured an identical RPGR variant as the father, there were phenotypic intrafamilial variations. The information on the variety of genotypic and phenotypic presentations in XLRP carriers is essential for further diagnosis, management, and monitoring of these cases, including the design of future gene therapy trials.

Visual contrast perception in visual snow syndrome reveals abnormal neural gain but not neural noise

Visual snow syndrome is a neurological condition characterised by a persistent visual disturbance, visual snow, in conjunction with additional visual symptoms. Cortical hyperexcitability is a potential pathophysiological mechanism, which could be explained by increased gain in neural responses to visual input. Alternatively, neural noise in the visual pathway could be abnormally elevated. We assessed these two potential competing neural mechanisms in our studies of visual contrast perception. Cortical hyperexcitation also occurs in migraine, which commonly co-occurs with visual snow syndrome. Therefore, to determine whether the effect of visual snow syndrome can be distinguished from interictal migraine, we recruited four participant groups: controls, migraine alone, visual snow syndrome alone, visual snow syndrome with migraine. In the first experiment, we estimated internal noise in 20 controls, 21 migraine participants, 32 visual snow syndrome participants (16 with migraine) using a luminance increment detection task. In the second experiment, we estimated neural contrast gain in 21 controls, 22 migraine participants, 35 visual snow syndrome participants (16 with migraine) using tasks assessing sensitivity to changes in contrast from a reference. Contrast gain and sensitivity were measured for the putative parvocellular and ON and OFF magnocellular pathways, respectively. We found that luminance increment thresholds and internal noise estimates were normal in both visual snow syndrome and migraine. Contrast gain measures for putative parvocellular processing and contrast sensitivity for putative OFF magnocellular processing were abnormally increased in visual snow syndrome, regardless of migraine status. Therefore, our results indicate that visual snow syndrome is characterised by increased neural contrast gain but not abnormal neural noise within the targeted pathways.

Visual snow syndrome and its relationship with migraine

INTRODUCTION

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.

DEVELOPMENT

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.

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.

The Psychiatric Symptomology of Visual Snow Syndrome

Objective: To characterise the psychiatric symptoms of visual snow syndrome (VSS), and determine their relationship to quality of life and severity of visual symptoms. Methods: One hundred twenty-five patients with VSS completed a battery of questionnaires assessing depression/anxiety, dissociative experiences (depersonalisation), sleep quality, fatigue, and quality of life, as well as a structured clinical interview about their visual and sensory symptoms. Results: VSS patients showed high rates of anxiety and depression, depersonalisation, fatigue, and poor sleep, which significantly impacted quality of life. Further, psychiatric symptoms, particularly depersonalisation, were related to increased severity of visual symptoms. The severity/frequency of psychiatric symptoms did not differ significantly due to the presence of migraine, patient sex, or timing of VSS onset (lifelong vs. later onset). Conclusion: Psychiatric symptoms are highly prevalent in patients with VSS and are associated with increased visual symptom severity and reduced quality of life. Importantly, patients with lifelong VSS reported lower levels of distress and milder self-ratings of visual symptoms compared to patients with a later onset, while being equally likely to experience psychiatric symptoms. This suggests that the psychiatric symptoms of VSS are not solely due to distress caused by visual symptoms. While no consistently effective treatments are available for the visual symptomology of VSS, psychiatric symptoms offer an avenue of treatment that is likely to significantly improve patient quality of life and ability to cope with visual symptoms.

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.

White matter abnormalities in a patient with visual snow syndrome: New evidence from a diffusion tensor imaging study

BACKGROUND

Visual snow syndrome (VSS) is a neurological condition characterized by flickering dots throughout the entire visual field. Both the pathophysiology and possible location of VSS are still under debate. White matter abnormalities were investigated using diffusion tensor imaging (DTI) in a patient with VSS.

METHODS

A 28-year-old patient with VSS and 10 healthy controls were investigated with DTI. Diffusion parametric maps were calculated and reconstructed using q-space diffeomorphic reconstruction. White matter pathways of the dorsal, ventral, integrative visual streams and thalamic connectivity were tracked. Then, they were applied to each subject's parameter map, stretched to the same length, and sampled along the tracts for regional analyses of DTI parameters.

RESULTS

Compared with healthy controls, our patient displayed higher axial diffusivity (AD) and radial diffusivity (RD) in the dorsal visual stream (cingulum, arcuate fasciculus, horizontal indirect anterior segment of the superior longitudinal fasciculus), in the ventral visual stream (fronto-occipital fasciculus, inferior longitudinal fasciculus) and in the integrative visual stream (indirect posterior component of the superior longitudinal fasciculus, vertical occipital fasciculus). Higher AD and RD were also detected in acoustic and optic radiations, and in thalamic radiations distal to the thalamus.

CONCLUSION

This VSS patient displayed multiple, bilateral white matter changes in the temporo-parieto-occipital junction in white matter pathways related to vision. We encourage the study of white matter pathology using DTI in complex neurological syndromes including VSS.

Visual snow syndrome: a review on diagnosis, pathophysiology, and treatment

PURPOSE OF REVIEW

Visual snow is considered a disorder of central visual processing resulting in a perturbed perception of constant bilateral whole-visual field flickering or pixelation. When associated with additional visual symptoms, it is referred to as visual snow syndrome. Its pathophysiology remains elusive. This review highlights the visual snow literature focusing on recent clinical studies that add to our understanding of its clinical picture, pathophysiology, and treatment.

RECENT FINDINGS

Clinical characterization of visual snow syndrome is evolving, including a suggested modification of diagnostic criteria. Regarding pathophysiology, two recent studies tested the hypothesis of dysfunctional visual processing and occipital cortex hyperexcitability using electrophysiology. Likewise, advanced functional imaging shows promise to allow further insights into disease mechanisms. A retrospective study now provides Class IV evidence for a possible benefit of lamotrigine in a minority of patients.

SUMMARY

Scientific understanding of visual snow syndrome is growing. Major challenges remain the subjective nature of the disease, its overlap with migraine, and the lack of quantifiable outcome measures, which are necessary for clinical trials. In that context, refined perceptual assessment, objective electrophysiological parameters, as well as advanced functional brain imaging studies, are promising tools in the pipeline.

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.

Visual snow syndrome: a comparison between an Italian and British population

BACKGROUND AND PURPOSE

Visual snow manifests as a pan-field, dynamic visual disturbance described as continuous television static-like tiny flickering dots. Current diagnostic criteria further require at least two additional symptoms for visual snow syndrome (VSS) from: palinopsia (afterimages and trailing); entoptic phenomena (floaters, blue field entoptic phenomenon, photopsia, self-light of the eye); photophobia and nyctalopia. Our objective was to compare the phenotype of VSS in an Italian and British population.

METHODS

Patients with VSS were characterized clinically using the current criteria. An online survey was prepared in collaboration with the patient group Eye-on-Vision. Patients were directed to the site if they contacted us by email asking to be involved in research. After data collection, we compared the phenotypic characteristics of a subgroup of British versus Italian patients taking part in the survey. As we expected more responses from the UK, we matched 100 UK patients for gender and age with our Italian cohort.

RESULTS

Patients were enrolled from the UK (n = 100) and Italy (n = 100). The populations had similar demography. After multiple correction testing there were no differences in VSS features between the two groups. The same was true for the prevalence of migraine and previous use of recreational drugs.

CONCLUSION

This is the first study comparing the phenotype of VSS between two distinct populations. Our findings suggest that the visual snow phenotype, as well as migraine comorbidity, is similar across the two groups.

Ocular motor measures of visual processing changes in visual snow syndrome

OBJECTIVE

To determine whether changes to cortical processing of visual information can be evaluated objectively using 3 simple ocular motor tasks to measure performance in patients with visual snow syndrome (VSS).

METHODS

Sixty-four patients with VSS (32 with migraine and 32 with no migraine) and 23 controls participated. Three ocular motor tasks were included: prosaccade (PS), antisaccade (AS), and interleaved AS-PS tasks. All these tasks have been used extensively in both neurologically healthy and diseased states.

RESULTS

We demonstrated that, compared to controls, the VSS group generated significantly shortened PS latencies (p = 0.029) and an increased rate of AS errors (p = 0.001), irrespective of the demands placed on visual processing (i.e., task context). Switch costs, a feature of the AS-PS task, were comparable across groups, and a significant correlation was found between shortened PS latencies and increased AS error rates for patients with VSS (r = 0.404).

CONCLUSION

We identified objective and quantifiable measures of visual processing changes in patients with VSS. The absence of any additional switch cost on the AS-PS task in VSS suggests that the PS latency and AS error differences are attributable to a speeded PS response rather than to impaired executive processes more commonly implicated in poorer AS performance. We propose that this combination of latency and error deficits, in conjunction with intact switching performance, will provide a VS behavioral signature that contributes to our understanding of VSS and may assist in determining the efficacy of therapeutic interventions.

Mirtazapine for treatment of visual snow syndrome: A case series with insights into pathophysiology and therapy

Background:

Patients with visual snow syndrome (VSS) describe tiny flickering dots in the entire visual field resembling the noise of a poorly adjusted channel of analogue television with additional symptoms. Little is known about the pathophysiology and therapeutic options for this debilitating condition.

Objectives:

We present a case series of three patients with VSS taking mirtazapine, one of the most often prescribed antidepressants, and discuss the utility of antidepressants by reviewing our current understanding of pathophysiology and therapy.

Results:

Mirtazapine has no effect on VSS, neither positive nor negative. This is in line with the reports from the literature suggested only some beneficial effects from lamotrigine.

Conclusions:

Since the pathophysiology of VSS is not fully understood, we still rely on the reports of individual cases or patient series. This includes not only the positive, but also the negative results to avoid unnecessary treatment trials. Looking into the literature, antidepressants do not seem to be a solution for the visual symptoms. So far, best data exists for the anticonvulsant lamotrigine.