Roshni Sengupta, PhD Scholar
Assistant Professor, Sushant University, Haryana, India
Defining- Visual Snow:
Visual Snow Syndrome (VSS) is a neurological condition that is characterised by the presence of “static” or “snow-like” visual disturbances in the field of vision. These disturbances can take the form of flickering dots, light flashes, or a general grainy quality to the visual field (as shown in Figure 1). The name “visual snow syndrome” was introduced by Dr. Goadsby and co-authors where they described the clinical characteristics, associated symptoms, and proposed a diagnostic criterion for VSS.(1) The prevalence of VSS is unknown being a rare condition. However, a 2015 study estimated the frequency of VSS to be roughly 0.9% of the general population and discovered that it is more prevalent in migraine sufferers. (2)
Although the specific origin of VSS is unknown, various explanations have been offered. According to one idea, it is caused by abnormalities in the brain’s visual pathways, notably in the way the brain interprets visual information. Another idea proposes that VSS is caused by changes in the structure or function of the retina. VSS may also be caused by a variety of factors, including genetic predisposition, environmental elements, and underlying medical disorders.
Figure 1: View with normal vision and view with visual snow
Clinical Classification of Symptoms of VSS:
VSS is often accompanied by other symptoms, such as migraine headaches, tinnitus (ringing in the ears), and tremors. VSS is a phenomenon that is often associated with chronic migraine aura, which is a type of migraine characterised by recurrent episodes of visual disturbances such as blind spots, zigzag lines, or flashing lights. While both VSS and chronic migraine aura can be symptoms of migraine, they are considered to be separate conditions.
VSS is a persistent condition with symptoms present 24/7, both with eyes closed and open, and independent of the outside light level. This contrasts with other visual disturbances, such as those associated with migraine, which typically have periods of remission when the symptoms are not present. It is often associated with other symptoms such as Palinopsia, trailing afterimages.(3) Hypersensitivity to light, i.e., photophobia and Entoptic phenomena are defined as “phenomena originating from visual system structures in response to specific stimulus.” (4) Typical phenomena include floaters, which are protein aggregations in the vitreous corpus, and the blue field entoptic phenomenon, which is caused by white blood cells in retinal blood vessels (5) casting shadows on photoreceptors.
Table 1: Proposed criteria for VSS, modified from Schankin et al. (6)
|A.||Visual snow: dynamic, continuous, tiny dots in the entire visual field lasting longer than 3 months|
|B.||Presence of at least two additional visual symptoms of the four following categories:
|C.||Symptoms are not consistent with typical migraine visual aura|
|D.||Symptoms are not better explained by another disorder (especially normal eye exams).|
Everyone experiences the same physical inputs that cause visual snow and other related phenomena. It is noteworthy that these mechanisms result in intense visual sensations in individuals with VSS, but not present in the normal population. One possible explanation for this discrepancy is that people who have visual snow may have a suppression deficiency in typical visual regulating networks, which leads to the persistence of visual snow and other visual symptoms. This shows that the underlying aetiology of visual snow may be connected to malfunction in brain networks involved in visual input regulation.
Recent study reveals that VS is linked to a dysfunction of the lingual gyrus; a particular region of the brain involved in visual information processing. Individuals with VS show aberrant activity in the lingual gyrus, notably in Brodmann area 19, which is also important in the control of visual information, according to research. (1)
VSS is still not completely understood, and until we do, patients’ capacity to manage with the condition is an important factor in enhancing quality of life. This includes making a definite diagnosis and reporting the adequacy of visual acuity and visual field. It is crucial to remember that VS symptoms might differ from person to person and range from mild to severe. In certain situations, the symptoms can be incapacitating and have a significant influence on an individual’s quality of life. To rule out other reasons and decide the best treatment choices, a precise diagnosis is required.
Keywords: Visual snow, migraine aura, visual pathway
- Schankin CJ, Goadsby PJ. Visual snow—persistent positive visual phenomenon distinct from migraine aura. Current pain and headache reports. 2015 Jun;19(6):1-6.
- Burch RC, Loder S, Loder E, Smitherman TA. The prevalence and burden of migraine and severe headache in the United States: updated statistics from government health surveillance studies. Headache: The Journal of Head and Face Pain. 2015 Jan;55(1):21-34.
- Critchley m. Types of visual perseveration: Paliopsia? And? Illusory visual spread? Brain. 1951 sep 1;74(3):267-99.
- Tyler CW. Some new entoptic phenomena. Vision research. 1978 Jan 1;18(12):1633-9.
- Sinclair SH, Azar-Cavanagh M, Soper KA, Tuma RF, Mayrovitz HN. Investigation of the source of the blue field entoptic phenomenon. Investigative ophthalmology & visual science. 1989 Apr 1;30(4):668-73.
- 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.
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