No structural lesion had been documented on cranial CT or MRI in visual snow. Some authors believe that is a form of visual processing error of sensitivity or gain but specific visual pathway lesions or a localized neurotransmitter imbalance in the brain parenchyma have not been proven. All of these conditions have been shown to share anomalies in lipid metabolism, particularly with allelic variants of the APOB gene. Investigations into scotopic sensitivity syndrome have identified similar features in ADHD, dyslexia, and chronic fatigue syndrome. There may be a family history of visual snow or migraine. Visual snow may occur even years after hallucinogenic drug use, and even after only one time use. The first comorbidity is Migraine, and in fact, many symptoms of migraine are also present in VS, such as fibromyalgia, tinnitus, among others.Īlthough typically isolated and idiopathic, several clinical disorders have been reported to occur with visual snow including stress, nonspecific anxiety, dyslexia, autism spectrum disorder, migraine with aura, or the use of recreational and prescription hallucinogenic drugs.
Other "networks" that have shown abnormalities in visual snow syndrome include: higher-level salience network, in addition to the previosly known thalamo-cortical pathways.
There are multiple advances on the understanding of this syndrome, with increasing functional and structural evidence that, as in migraine, the origin of visual snow is "widespread cortical dysfunction", with secondary cortical hyperexcitability. Initial results showed that patients with visual snow have both cortical hyperexcitability and loss of inhibition of visual processing in V1 (confirming thalamo-cortico dysrhythmia), different from migraine alone. Subjects included controls, migraineurs and patients with visual snow. There are ongoing trials to study, and further confirm, the cortical origin and thalamo-cortico dysrhythmia as cause of visual snow using MEG (magnetic encephalography testing). Theorized to be caused by thalamo-cortical dysrhythmia but may be associated with persistent migraine with aura or as a feature of hallucinogenic persisting perception disorder. In recent studies, it was found that the primary and secondary visual areas of the brain are "hyper-excited", confirmed by both radiological and electrophysiological studies. The etiology is hypersensitivity to internal and external stimuli. Another study in the UK found a prevalence of 2.2% of individuals in the study meeting criteria for Visual Snow, with a mean age of 50.6 years which is considerably higher than previously thought. In one study the mean age of onset of symptoms was 21 years old but it can occur at any age, in either gender, and in any race. Visual snow symptoms commonly appear during the late teenage years and early adulthood. It is recently known to be associated to psychiatric conditions including anxiety, depression, depersonalisation, fatigue, poor sleep/poor rest, among others DiseaseĪlternate names for Visual Snow are Scotopic Sensitivity Syndrome, Meares-Irlen Syndrome, Persistent Visual Phenomena, Visual Stress, Visual Static, and Asfedia. It has been recently hypothezised that the pathology of visual snow is similar to migraine. In the Broadband type the dots noise is bipolar and occurs in contrast to the background: with a light background the dots will appear dark, and with a dark background the dots will appear light. In black pulse visual snow, the dots are always darker than their background, whereas in white pulse the dots are always lighter than their background. In the Pulse type the dots are the same color as their background, black or white, and the noise is monopolar. Visual snow exists in one of two forms: the pulse type and the broadband type. The dots remain individual and do not clump together or change in size. Visual snow (VS) is a form of visual hallucination that is characterized by the perception of small, bilateral, simultaneous, diffuse, mobile, asynchronous dots usually throughout the entire visual field, but it can be partial, and it is present in all conditions of illumination, even with the eyes closed.
2.5 Diagnostic Procedures/Laboratory Tests.
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