Visual Snow Syndrome

Disease Overview

Summary

Visual snow is a neurological disorder characterized by a continuous visual disturbance that occupies the entire visual field and is described as tiny flickering dots that resemble the noise of a detuned analogue television. In addition to the static, or “snow”, affected individuals can experience additional visual symptoms such as visual images that persist or recur after the image has been removed (palinopsia); sensitivity to light (photophobia); visual effects originating from within the eye itself (entoptic phenomena) and impaired night vision (nyctalopia).

The prevalence of visual snow in the general population is currently unknown. The average age of the visual snow population seems to be younger than for many other neurological disorders. This early onset, combined with a general lack of recognition by health care providers, suggests it is an uncommon problem.

Research has been limited because of issues of case identification and diagnosis, the latter now largely addressed, and the limited size of any studied cohort. Initial functional brain imaging research suggests visual snow is a brain disorder.

Visual snow is a chronic condition, sometimes highly disabling, uncommon condition that needs collaborative research and lateral thinking to make progress towards understanding, treatment and cure.

Introduction

Since its first description ¹, the introduction of the term visual snow ² and its formal clinical definition ³, visual snow is now being recognized by physicians and scientists as a new disease entity. The first literature reports of visual snow mostly represented isolated clinical descriptions in the context of larger groups of patients affected by persistent visual disturbance, previously defined as “persistent positive visual phenomena” ¹.

Visual snow has been misdiagnosed in case series being mixed with persistent migraine aura, which has led to mechanistic confusion, diagnostic imprecision ⁴ and use of treatments that have not been useful ⁵. Visual snow has been considered to be the same condition as hallucinogen persisting perception disorder (HPPD) ⁶. Although it seems hallucinogens can trigger a similar disturbance ⁷, it is clear visual snow syndrome can be entirely independent of drug triggers. Lastly, many patients are told that their symptoms are not part of a disease. These issues have delayed recognition of the syndrome.

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Synonyms

• visual static
• persistent positive visual phenomena
• VSS

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Signs & Symptoms

The main clinical feature of the syndrome described consistently by affected people is an unremitting, positive visual phenomena, present in the entire visual field and characterized by uncountable tiny flickering dots interposed between the person’s vision and the background. This ‘static’ is typically black and white but can also be colored, flashing or transparent.

In addition to the static, or snow, people can experience additional visual symptoms of either direct neurological origin, such as:

• Seeing something when it’s not there (palinopsia)
• Sensitivity to light (photophobia)
• Night blindness (nyctalopia)
• Visual perceptions that arise from inside the eye rather than the outside world (entoptic phenomena)
  • Entoptic phenomena that are found (either alone or in combination) are the blue field entoptic phenomenon, floaters (the perception of which is defined as myodesopsia), self-light of the eye and spontaneous photopsia.

Up to 75% of individuals with visual snow report at least three of these four secondary visual problems, which along with the static itself form the “visual snow syndrome”³. It is important for researchers and clinicians to distinguish visual snow from other phenomena and to recognize the associated symptoms ⁸. Most of these can be experienced by healthy individuals (especially in the case of floaters or retinal afterimages, a visual illusion that occurs when you look at something bright or for a long time and then look away), or by patients with ophthalmological diseases; the key difference with visual snow is that they manifest in a recurring, debilitating and persistent manner and in the context of a perfectly functional optic apparatus.

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Causes

Currently, the exact causes of visual snow syndrome (VSS) are unknown. However, researchers think it may involve issues with how the brain processes visual information rather than a problem with the eyes. ^10,11,12

• The primary symptom of VSS, visual static, is a whole-field disturbance. This suggests that the problem is unlikely to be in the eyes, optic nerves, or primary visual cortex, which processes direct visual input.
• Other symptoms, like palinopsia (afterimages or trailing effects) and enhanced entoptic phenomena (seeing visual patterns like floaters), also point to a neurological origin since these occur despite normal eye exam results.

• A neuroimaging study using [18F]-FDG PET scans found increased activity (hypermetabolism) in the lingual gyrus, part of the brain’s visual cortex.
  • The lingual gyrus is essential for functions like visual memory, color perception and recognizing facial expressions. It’s also involved in conditions like photophobia (light sensitivity).

Other theories include: ^10,11,12

• The visual cortex may be overly sensitive which could explain the persistent visual disturbances.
• A disruption in the communication between the thalamus (a brain structure that processes sensory signals) and the cortex may play a role.

These initial findings are promising, but more studies involving larger groups of people with VSS are needed to confirm these ideas. Further research could help identify specific causes and pave the way for more effective treatments.

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Affected populations

It is currently unknown how many patients suffer from visual snow worldwide. The available data tells us that there is possibly a higher prevalence of the disease in males and that the average age of affected people is relatively young ¹³.

The onset of symptoms can be in very early life, with most people presenting symptoms for their entire lifetime. Some people have a sudden and unpredictable onset of the disease; this occasionally, but not necessarily, follows an identifiable cause.

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Disorders with Similar Symptoms

A disorder which has been strongly related to visual snow is tinnitus. Tinnitus is a common condition often referred to as a “ringing in the ears” and characterized by the perception or sensation of sound even though there is no identifiable external source for the sound. Tinnitus is extremely frequent in patients with visual snow, with up to three quarters of affected people reporting the symptom ¹⁴. This has led some researchers to hypothesize a possible relationship between the two conditions, which both possibly represent a similar dysfunction in sensory processing, respectively of the visual and auditory system in the brain.

The differential diagnosis of visual snow includes prolonged migraine aura. The relationship between migraine and visual snow is a complex one; it has been in fact proven that migraine can aggravate the clinical presentation of the visual snow syndrome and that it has a higher prevalence in this disorder than in the general population ⁹.

Visual aura, on the other hand, does not alter the typical symptoms of visual snow, but also often occurs with the condition. These two disorders, however, should not be confused; it is important to remember the main difference, which is the unremitting characteristic as well as the panfield visual disturbance in the case of visual snow, as opposed to a transient disorder which normally occupies only a specific area of the visual field in migraine aura.

Visual snow should also be distinguished from hallucinogen persisting perception disorder (HPPD) ^6,15,16. This disorder is characterized by a presence of sensory and particularly visual disturbances and shares with visual snow the characteristic of being continuous and sometimes unremitting. It is, however, necessarily associated with the consumption of hallucinogenic substances, which is certainly not a prerequisite of visual snow, because it has been reported even in young children.

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Diagnosis

Visual snow syndrome is a clinical diagnosis that comes from the fulfillment of a set of criteria and the exclusion of secondary causes of similar visual disturbances, such as underlying ophthalmological and neurological diseases.

Criteria diagnosis for visual snow syndrome have been published ³ and includes:

• Presence of the primary symptom: visual snow, which refers to tiny, dynamic dots that appear continuously across the entire field of vision for more than 3 months. These dots can look different depending on the background:
  • Black/grey dots on a white background
  • Grey/white dots on a black background
  • They may also appear as transparent, white flashing, or colored dots
• Presence of at least two of the following additional visual symptoms:
  • Palinopsia: This includes either:
    • Afterimages: Seeing an image even after looking away (unlike normal retinal afterimages, which are brief and in complementary colors)
    • Trailing of moving objects: Objects appear to leave a trail behind them as they move
  • Enhanced entoptic phenomena: These originate from the visual system itself and include:
    • Excessive floaters: Dark or transparent shapes floating in the visual field of both eyes
    • Blue field entoptic phenomenon: Numerous small dots or rings moving quickly across the visual field, especially visible against a bright, uniform background like a blue sky
    • Self-light of the eye: Colored waves or patterns seen when closing eyes in darkness
    • Spontaneous photopsia: Flashes of bright light that occur spontaneously
  • Photophobia: Increased sensitivity to light that can be uncomfortable or painful
  • Nyctalopia: Difficulty seeing in low-light or nighttime conditions

• Differentiation from migraine visual aura

• VSS symptoms must not match the typical visual aura seen in migraines (as defined by the International Headache Society). Migraine auras are temporary, localized and usually occur before a headache, unlike the continuous symptoms of VSS.

• Exclusion of other causes
  • Symptoms cannot be explained by another condition
  • Normal results from an eye examination or neurological tests
  • Not caused by previous use of psychotropic medications or other substances

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Standard Therapies

Treatment

The lack of knowledge on the basic biology of the visual snow syndrome has caused a general lack of effective treatment strategies for most affected people.

Drugs like migraine preventives, antidepressants, or pain relievers have shown inconsistent results. Lamotrigine has had some positive effects in some people but lacks robust evidence from clinical trials.

Objective documentation of eye movement dysfunctions and advanced brain imaging studies are needed to determine the neural mechanisms underlying VSS.

Two promising therapeutic approaches have emerged, but larger studies are needed to confirm their efficacy.

1. • Chromatic tint therapy is colored filters that help reduce the perception of visual snow, palinopsia, photopsia and light sensitivity.
   • Oculomotor-based therapy techniques targeting eye movement and saccadic tracking have been shown to reduce palinopsia and improve visual clarity.

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Clinical Trials and Studies

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. Government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: [email protected]

Some current clinical trials also are posted on the following page on the NORD website:
https://rarediseases.org/living-with-a-rare-disease/find-clinical-trials/

For information about clinical trials sponsored by private sources, contact:
www.centerwatch.com

For information about clinical trials conducted in Europe, contact:
https://www.clinicaltrialsregister.eu/

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References

JOURNAL ARTICLES

1. Liu GT, Schatz NJ, Galetta SL, Volpe NJ, Skobieranda F, Komorsky GS. Persistent positive visual phenomena in migraine. Neurology. 1995;45:664-8.
2. Jager HR, Giffin NJ, Goadsby PJ. Diffusion- and perfusion-weighted MR imaging in persistent migrainous visual disturbances. Cephalalgia. 2005;25:323-32.
3. Schankin CJ, Maniyar FH, Digre KB, Goadsby PJ. Visual snow- a disorder distinct from persistent migraine aura. Brain. 2014;137:1419-28.
4. Rothrock JF. Successful treatment of persistent migraine aura with divalproex sodium. Neurology. 1997;48:261-2.
5. Puledda F, Lau T, Schankin C, Goadsby PJ. Treatment effect in visual snow. Cephalalgia. 2017;37(1S):231-2.
6. American Psychiatric Association. Hallucinogen Persisting Perception Disorder. Diagnostic and Statistical Manual of Mental Disorders. 5th ed. Arlington, VA: American Psychiatric Publishing; 2013. p. 531-2.
7. Ffytche DH. Visual hallucinatory syndromes: past, present, and future. Dialogues in clinical neuroscience. 2007;9(2):173-89.
8. Bessero AC, Plant GT. Should ‘visual snow’ and persistence of after-images be recognised as a new visual syndrome? J Neurol Neurosurg Psychiatry. 2014;85:1057-8.
9. 9.Schankin CJ, Maniyar FH, Sprenger T, Chou DE, Eller M, Goadsby PJ. The relation between migraine, typical migraine aura and “visual snow”. Headache. 2014;54(6):957-66.
10. Bou Ghannam A, Pelak VS. Visual Snow: a Potential Cortical Hyperexcitability Syndrome. Curr Treat Options Neurol. 2017;19(3):9.
11. McKendrick AM, Chan YM, Tien M, Millist L, Clough M, Mack H, et al. Behavioral measures of cortical hyperexcitability assessed in people who experience visual snow. Neurology. 2017;88(13):1243-9.
12. Lauschke JL, Plant GT, Fraser CL. Visual snow: A thalamocortical dysrhythmia of the visual pathway? J Clin Neurosci. 2016;28:123-7.
13. Puledda F, Schankin C, Goadsby PJ. Visual Snow Syndrome: what we know so far. Current Opinion in Neurology. 2018;31:52-8.
14. Puledda F, Lau T, Schankin C, Goadsby PJ. CLINICAL CHARACTERIZATION OF VISUAL SNOW. Cephalalgia. 2017;37(1S):177.
15. Abraham HD. Visual phenomenology of the LSD flashback. Arch Gen Psychiatry. 1983;40(8):884-9.
16. Abraham HD, Aldridge AM. Adverse consequences of lysergic acid diethylamide. Addiction. 1993;88(10):1327-34.
17. Headache Classification Committee of the International Headache Society (IHS). The International Classification of Headache Disorders, 3rd Edition. Cepahalalgia. 2018;38:1-211.
18. Unal-Cevik I, Yildiz FG. Visual Snow in Migraine With Aura: Further Characterization by Brain Imaging, Electrophysiology, and Treatment – Case Report. Headache. 2015.

INTERNET

Visual Snow Initiative: Conference on May 8, 2018. https://www.visualsnowinitiative.org/2018-visual-snow-conference/ Accessed Dec 3, 2024.

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