Visual snow syndrome

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Visual snow syndrome
Other namesPersistent positive visual phenomenon, [1] visual static, aeropsia
Illustration of visual snow.jpg
Illustration of visual snow
Specialty Neurology, neuro-ophthalmology
Symptoms Static and auras in vision, palinopsia, blue field entoptic phenomenon, nyctalopia, tinnitus
Complications Poor quality of vision, photophobia, heliophobia, depersonalization and derealization [2]
Usual onsetVisual snow can appear at any time, but it commonly appears at birth, late teenage years, and early adulthood.
Causes Unknown, [3] hyperexcitability of neurons and processing problems in the visual cortex [4] [5]
Risk factors Migraine sufferer, [6] psychoactive substance use
Differential diagnosis Migraine aura, [7] persistent aura without infarction, hallucinogen persisting perception disorder [8] [9]
Medication Anticonvulsants [7] [3] (limited evidence and success)
FrequencyUncommon (understudied)

Visual snow syndrome (VSS) is an uncommon neurological condition in which the primary symptom is visual snow, a persistent flickering white, black, transparent, or colored dots across the whole visual field. [7] [4] It is distinct from the symptom of visual snow itself, which can also be caused by several other causes; these cases are referred to as "VSS mimics." [10] Other names for the syndrome include "scotopic sensitivity syndrome", "Meares-Irlen syndrome", and "asfedia." [11]

Contents

Other common symptoms are palinopsia, enhanced entoptic phenomena, photophobia, and tension headaches. [12] [13] The condition is typically always present and has no known cure, as viable treatments are still under research. [14] Astigmatism, although not presumed connected to these visual disturbances, is a common comorbidity. Migraines and tinnitus are common comorbidities that are both associated with a more severe presentation of the syndrome. [15]

The cause of the syndrome is unclear. [3] The underlying mechanism is believed to involve excessive excitability of neurons in the right lingual gyrus and left anterior lobe of the cerebellum. Another hypothesis proposes that visual snow syndrome could be a type of thalamocortical dysrhythmia and may involve the thalamic reticular nucleus (TRN). A failure of inhibitory action from the TRN to the thalamus may be the underlying cause for the inability to suppress excitatory sensory information. [4] [6] Research has been limited due to issues of case identification, diagnosis, and the limited size of any studied cohort, though the issue of diagnosis is now largely addressed. Initial functional brain imaging research suggests visual snow is a brain disorder. [16]

Difference from visual snow

Visual snow – the symptom – may sometimes be a transient experience, and it is possible that it is a natural phenomenon, sometimes thought to be visible to many people if they focus on it. [17] In visual snow syndrome, however, visual snow is ever-present, regardless of lighting conditions and even when the eyes are closed. [18] In contrast to visual phenomena caused by migraines, which can last up to about an hour, static caused by visual snow syndrome lasts continuously for several months. [18]

If visual snow is persistent, continuous, and accompanied by other symptoms, such as entoptic phenomenon, palinopsia, photophobia and/or nyctalopia – it may indicate visual snow syndrome. [18] This syndrome is not just a phenomenon, but a neurological condition, [18] where a person experiences constant visual disturbances, regardless of lighting conditions. [18] Visual snow syndrome is linked to heightened neural sensitivity in the visual regions of the brain. [19] However, it is important not to confuse it with other causes of visual snow, sometimes referred to as VSS mimics. [10]

Signs and symptoms

Visual snow likely represents a clinical continuum, with different degrees of severity. The presence of comorbidities such as migraine and tinnitus is associated with a more severe presentation of visual symptoms. [15]

Non-visual symptoms may include difficulty concentrating, insomnia, frequent migraines, nausea, and vertigo. [20]

Diagnosis

Visual snow syndrome is usually diagnosed with the following proposed criteria: [21] [22] [15]

Additional and non-visual symptoms like tinnitus, ear pressure, brain fog, and more might be present. It can also be diagnosed by PET scan.[ citation needed ]

Mimics

The following conditions other than visual snow syndrome can also cause visual snow symptoms, and care must be taken not to confuse them with it: [23]

It must also be distinguished from migraine with visual aura. [23]

Common misconceptions

Comorbidities

Migraine and migraine with aura are common comorbidities. However, comorbid migraine worsens some of the additional visual symptoms and tinnitus seen in "visual snow" syndrome. This might bias research studies by patients with migraine being more likely to offer study participation than those without migraine due to having more severe symptoms. In contrast to migraine, comorbidity of typical migraine aura does not appear to worsen symptoms. [6]

Non-visual symptoms of visual snow can include depersonalization, derealization, depression, photophobia, and heliophobia in the individual affected. [2]

Patients with visual "snow" have normal equivalent input noise levels and contrast sensitivity. [31] In a 2010 study, Raghaven et al. hypothesize that what the patients see as "snow" is eigengrau. [31] This would also explain why many report more visual snow in low light conditions: "The intrinsic dark noise of primate cones is equivalent to ~4000 absorbed photons per second at mean light levels; below this the cone signals are dominated by intrinsic noise". [32] [33]

Causes

The causes of VSS are not clear. [3] The underlying mechanism is believed to involve excessive excitability of neurons within the cortex of the brain, [4] specifically the right lingual gyrus and left cerebellar anterior lobe of the brain. [6]

Persisting visual snow can feature as a leading addition to a migraine complication called persistent aura without infarction, [34] commonly referred to as persistent migraine aura (PMA). In other clinical sub-forms of migraine headache may be absent and the migraine aura may not take the typical form of the zigzagged fortification spectrum (scintillating scotoma), but manifests with a large variety of focal neurological symptoms. [35]

Visual snow does not depend on the effect of psychotropic substances on the brain. [15] Hallucinogen persisting perception disorder (HPPD), a condition caused by hallucinogenic drug use, is sometimes linked to visual snow, [36] but both the connection of visual snow to HPPD [8] and the cause and prevalence of HPPD are disputed. [9] Most of the evidence for both is generally anecdotal and subject to spotlight fallacy. [8] [9] Visual snow has also been correlated with head trauma and infection. [37]

Recent studies

Treatments

It is difficult to resolve visual snow with treatment, but it is possible to reduce symptoms and improve quality of life through treatment, both of the syndrome and its comorbidities. [4] In some studies, lamotrigine as a treatment for visual snow syndrome only showed efficacy in 20% of patients, and in one study, patients using lamotrigine even reported worsening symptoms. [43] Medications that may be used include lamotrigine, acetazolamide, verapamil, [4] clonazepam, propranolol, and sertraline [44] but these do not always result in positive effects. [7] [3] As of 2021, two ongoing clinical trials were using transcranial magnetic stimulation and neurofeedback for visual snow. [45] [46]

A recent study in the British Journal of Ophthalmology has confirmed that common drug treatments are generally ineffective in visual snow syndrome (VSS). Vitamins and benzodiazepines, however, were shown to be beneficial in some patients and can be considered safe for this condition. [47]

References

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