Visual snow syndrome
Other names	Persistent positive visual phenomenon,[1] visual static, aeropsia
Animated example of visual snow-like noise
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 onset	Visual 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)
Frequency	Uncommon (understudied)

Visual snow syndrome (VSS) is a form of visual hallucination that is characterized by the perception of small, flickerg dots throughout the visual field. It is present in all conditions of illumination. The dots remain individual and do not clump together or change in size. Visual snow exists in two forms: the pulse type and the broadband type.

In the pulse type, the dots are the same color as their background and tend to flicker individually, sometimes suggestive of raindrops on a car windshield.^[10] In black pulse visual snow, the dots are darker than their background, whereas in white pulse the dots are lighter than their background.

In the broadband type, the noise is perceived as a coarse texture.^[10] The 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.^[7][4]

Other common symptoms are palinopsia, enhanced entoptic phenomena, photophobia, and tension headaches.^[11][12] The condition is typically always present and has no known cure, as viable treatments are still under research.^[13] Astigmatism, although not presumed connected to these visual disturbances, ciated with a more severe presentation of the syndrome.^[14] Temporomandibular joint dysfunction (TMJ) may also be a common comorbidity.^{[citation needed]}

The cause of the syndrome is unclear.^[3] The underlying mechanism is believed to involve excessive excitability of neurons in the right is, 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.

Signs and symptoms

In addition to visual snow, many of those affected have other types of visual disturbances such as starbursts, increased afterimages, floaters, trails, and many others.^[15]

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 the visual symptoms.^[14]

Diagnosis

Visual snow syndrome is usually diagnosed with the following proposed criteria:^[16][17][14]

• Visual snow: dynamic, continuous, tiny dots observed across the entire visual field at any time of the day, regardless of lighting conditions, persisting for more than three months.
  • The dots are usually black/gray on a white background and gray/white on a black background; however, they can also be transparent, white flashing, or colored.
• Presence of at least 2 additional visual symptoms of the 4 following categories:
  • i. Palinopsia. At least 1 of the following: afterimages or trailing of moving objects.
  • ii. Enhanced entoptic phenomena. At least 1 of the following: excessive floaters in both eyes, excessive blue field entoptic phenomenon, self-light of the eye (phosphenes), or spontaneous photopsia.
  • iii. Photophobia.
  • iv. Nyctalopia; impaired night vision.
• Symptoms are not consistent with typical migraine aura.
• Symptoms are not better explained by another disorder (ophthalmological, drug abuse).
  • Normal ophthalmology tests (best-corrected visual acuity, dilated fundus examination, visual field, and electroretinogram); not caused by previous intake of psychotropic drugs.

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

What is not visual snow?

1. Perceiving visual static, flickering, or graininess on monochrome colors, in the sky, or in darkness can be a normal phenomenon associated with neural noise, amplified in the absence of bright visual stimuli. This effect is known as the Ganzfeld Effect (Wiki)/ Ganzfeld Effect (External Source), Eigengrau. In conditions of low illumination, especially in dimly lit environments, this phenomenon is related to how the eyes and the brain process visual information in insufficient lighting. The visual system becomes more sensitive to light and can amplify noise or minor changes in visual signals. It's important to note that the perception of such phenomena may vary among different individuals due to individual differences in perception and sensitivity.
2. When the eyes are closed, visual static may be related to the first level of visual hallucination.
3. Eye pathologies or other neurological conditions can also be a cause of visual anomalies, including the appearance of visual static or other changes in perception. Additionally, psychological disorders, such as somatic disorders, could potentially contribute to these perceptual disturbances.

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]

Psychological side effects 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.^[18] In a 2010 study, Raghaven et al. hypothesize that what the patients see as "snow" is eigengrau.^[18] 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".^[19]

Causes

The causes are unclear.^[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,^[20] 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.^[21]

Visual snow does not depend on the effect of psychotropic substances on the brain.^[14] Hallucinogen persisting perception disorder (HPPD), a condition caused by hallucinogenic drug use, is sometimes linked to visual snow,^[22] but both the connection of visual snow to HPPD^[8] and the cause and prevalence of HPPD is disputed.^[9] Most of the evidence for both is generally anecdotal, and subject to spotlight fallacy.^[8][9]

In the case of psychological causes, the observation of increased visual noise may be attributed to the body's response to stress, anxiety, or excessive obsessive attention to the normal phenomenon of visual perception. Additionally, somatic obsessive-compulsive disorder (OCD) factors could contribute to such visual disturbances.

Timeline

• In May 2015, visual snow was described as a persisting positive visual phenomenon distinct from migraine aura in a study by Schankin and Goadsby.^[23]
• In December 2020, a study^[24] found local increases in regional cerebral perfusion in patients with visual snow syndrome.
• In September 2021, two studies^[25] found white matter alterations in parts of the visual cortex and outside the visual cortex in patients with visual snow syndrome.
• In November 2023, a study^[26] revealed that glutamate and serotonin are involved in brain connectivity alterations in areas of the visual, salience, and limbic systems in VSS. Importantly, altered serotonergic connectivity is independent of migraine in VSS, and simultaneously comparable to that of migraine with aura, highlighting a shared biology between the disorders.

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] Medications that may be used include lamotrigine, acetazolamide, verapamil,^[4]clonazepam, propranolol, sertraline^[27] but these do not always result in benefits.^[7][3] As of 2021, there were two ongoing clinical trials using transcranial magnetic stimulation and neurofeedback for visual snow.^[28][29]

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.^[30]