A brief introduction to visual snow syndrome 

Raiyan Rubab 
Integrated Science, Class of 2025, McMaster University 

Visual Snow Syndrome (VSS) is a neurological disorder characterized by a wide array of visual symptoms. Its defining symptom is the titular visual snow, which involves seeing constant flickers of innumerable tiny dots across the visual field.1 The observed static is typically black and white, though it might be colorful in other circumstances. The intensity of the static may also vary with ambient luminosity, texture or color of the background.2 

VSS is a rare disease that was first discovered in 1995 by Dr. Christopher J. Schankin. Only 200 cases of VSS had been documented in scientific literature by 2018.3 While the exact prevalence is unknown, it is estimated that up to 2.2% of the global population is affected by the syndrome.1 40% of VSS patients report lifelong experiences of visual disturbances. Patients with late onset of symptoms generally experienced visual disturbances in the second or third decades of their lives.4 Most of them also exhibited comorbidity with tinnitus and migraine with or without aura.2 In fact, the comorbidity with migraines and rarity of VSS often led to its misdiagnosis as simple migraine auras. Auras are sensory disturbances such as bright dots, sparks, etc. that occur shortly before a migraine attack. Failed treatments with migraine medicines and recent advances in the pathophysiology of VSS have proven that the syndrome is not the same as migraines.3 The separation of the syndrome from migraines has changed the diagnostic criteria for VSS as well. The new diagnostic criteria states that to be diagnosed with VSS, a patient needs to exhibit persistent visual snow lasting more than 3 months and at least two of the following symptoms: Trailing-after image (Figure 1c), rapid movement of tiny dots on wiggly paths (Figure 1d), light sensitivity, or impaired night vision (Figure 1e).4 

Figure 1: a) normal vision b) visual snow c) Palinopsia or trailing after-image d) other common visual symptoms such as excessive floaters, phosphenes, colored blobs, and enhanced entoptic phenomenon which is the rapid movement of tiny dots on wiggly paths e) Nyctalopia or impaired night vision and f) a composite picture of all shown visual symptoms which mimics the vision of a patient with severe VSS (3).

Recent development in the pathophysiological field has yielded a few hypotheses for VSS. However, the exact nature of the mechanism behind it is still unknown. One such theory is that cortical hyperexcitability or reduced habituation to repeated visual stimuli observed in VSS patients with migraines allows them to sense visual stimuli below threshold levels.3 This is supported by the “Stochastic Resonance” theory, which suggests that introducing certain levels of noise in a system may increase the visual system’s sensitivity to weak stimuli.5 On the other hand, some argue that VSS is not a disease but a default state of vision. Hence, the symptoms pertaining to VSS are not acquired by the patients, instead they are actively suppressed by healthy humans. Surprisingly, VSS has not been observed to significantly heighten activity in the primary visual cortex of the patients despite being a visual syndrome.

The visual symptoms could also be just hallucinations. VSS patients do show higher rates of anxiety and depression and may also suffer from traditionally psychotic symptoms such as depersonalization and derealization. Severe visual symptoms also result in sleep deprivation which may induce hallucinations. Even patients with chronic VSS suffer from anxiety and depression, despite reporting reduced distress due to the symptoms in comparison to patients with late-onset VSS. However, one of the baseline requirements for VSS diagnosis includes confirming the absence of other etiologies such as psychosis or drug use that might cause hallucinations. As such, the demographic of patients partaking in the original VSS studies showed no other neurological, psychotic, or ophthalmological disorders and had no record of drug usage in the past.6 This could prove that VSS is not a psychotic, but a neurological disease.

Visual Snow Syndrome is still a medical mystery due to its rarity and frequent misdiagnosis. The current data hints at a possible cure in the anti-seizure drug, Lamotrigine, however treatment is still dependent on the subjective experiences of the patients.1 Consequently, the only objective way to improve the quality of life of VSS patients is to provide psychiatric treatment to avoid intensifying the visual disturbances. 

​1. Klein A, Schankin CJ. Visual Snow Syndrome as a Network Disorder: A Systematic Review. Front Neurol [Internet]. 2021 [cited 2022 Jan 15];12. Available from: https://www.frontiersin.org/article/10.3389/fneur.2021.724072 
2. Schankin CJ, Maniyar FH, Digre KB, Goadsby PJ. ‘Visual snow’ – a disorder distinct from persistent migraine aura. Brain. 2014 May 1;137(5):1419–28.  
3. Metzler AI, Robertson CE. Visual Snow Syndrome: Proposed Criteria, Clinical Implications, and Pathophysiology. Curr Neurol Neurosci Rep. 2018 Jun 22;18(8):52.  
4. Solly EJ, Clough M, Foletta P, White OB, Fielding J. The Psychiatric Symptomology of Visual Snow Syndrome. Front Neurol. 2021 Jul 30; 12:703006.
5. Harper DW. Signal Detection Analysis of Effect of White Noise Intensity on Sensitivity to Visual Flicker. Percept Mot Skills. 1979 Jun 1;48(3):791–8.  
6. Liu GT, Schatz NJ, Galetta SL, Volpe NJ, Skobieranda F, Kosmorsky GS. Persistent positive visual phenomena in migraine. Neurology. 1995 Apr 1;45(4):664–8. ​ 

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