Visual Snow

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Article initiated by:
Aroucha Vickers, DO, Claudia Prospero Ponce, MD, Travis Mitchell
All contributors:
Akaanksh Shetty, Aroucha Vickers, DO, Claudia Prospero Ponce, MD
Assigned editor:
Claudia Prospero Ponce, MD
Review:
Assigned status Update Pending
 by Claudia Prospero Ponce, MD on July 15, 2024.


Disease Entity

Visual snow (VS) is a form of visual hallucination characterized by the perception of small, bilateral, simultaneous, diffuse, mobile, asynchronous dots usually throughout the entire visual field but sometimes occurring partially. It is present in all conditions of illumination, even with the eyes closed. The dots remain individual and do not clump together or change in size. Visual snow exists in 1 of 2 forms:

  • In the pulse type, the dots are the same color as their background, black or white, and the noise is monopolar. In black pulse VS, the dots are always darker than their background, whereas in white pulse, the dots are always lighter than their background.
  • In the broadband type, the dot 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.[1] [2]


It has recently been hypothesized that the pathology of visual snow is similar to migraine. In addition, VS syndrome is known to be associated with psychiatric conditions including anxiety, depression, depersonalization, fatigue, and poor sleep/rest.[3]

Disease

Alternate names for visual snow are scotopic sensitivity syndrome, Meares-Irlen syndrome, persistent visual phenomena, visual stress, visual static, and asfedia.

Epidemiology

Visual snow symptoms commonly appear during the late teenage years and early adulthood. In one study, the mean age of symptom onset was 21 years, but it can occur at any age, in either gender, and in any race. Another study in the UK found a prevalence of 2.2% of individuals meeting criteria for visual snow, with a mean age of 50.6 years, which is considerably higher than previously thought. [1] [4] [5]

Etiology

The etiology of VS is hypersensitivity to internal and external stimuli. In recent studies, it was found that the primary and secondary visual areas of the brain are "hyperexcited," confirmed by both radiological and electrophysiological studies. [6]

Visual snow is most often idiopathic. It is theorized to be caused by thalamo-cortical dysrhythmia but may be associated with persistent migraine with aura or a feature of hallucinogenic persisting perception disorder.[7] There are ongoing trials to study and further confirm the cortical origin and thalamo-cortical dysrhythmia as a cause of visual snow using magnetoencephalography (MEG). Subjects included controls, migraineurs, and patients with visual snow. Initial results showed that patients with visual snow have both cortical hyperexcitability and loss of inhibition of visual processing in V1 (confirming thalamo-cortical dysrhythmia), different from migraine alone.

There have been multiple advances in the understanding of this syndrome,[3][8] with increasing functional and structural evidence that, as in migraine, the origin of visual snow is "widespread cortical dysfunction," with secondary cortical hyperexcitability. Other networks that have shown abnormalities in VS syndrome include the higher-level salience network, in addition to the previously known thalamo-cortical pathways.[8]

Risk Factors

The first comorbidity is migraine; in fact, many symptoms of migraine are also present in VS, such as fibromyalgia and tinnitus, among others.

Although VS is typically isolated and idiopathic, several clinical disorders have been reported to occur with visual snow, including stress, nonspecific anxiety, dyslexia, autism spectrum disorder, and migraine with aura, as well as the use of recreational and prescription hallucinogenic drugs. Visual snow may occur even years after hallucinogenic drug use, and even after only one-time use. It is important to rule out current use of other hallucinogens like LSD and magic mushrooms (psilocybin). There also may be a family history of visual snow or migraine. [7] Investigations into scotopic sensitivity syndrome have identified similar features in ADHD, dyslexia, and chronic fatigue syndrome. All of these conditions have been shown to share anomalies in lipid metabolism, particularly with allelic variants of the APOB gene. [9]

General Pathology

Some authors believe that VS 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. No structural lesion had been documented on cranial CT or MRI in visual snow,[1] but a 2021 study has proven changes of alpha and gamma waves in MEG.[10]

Pathophysiology

The exact pathophysiology of VS is unknown, but studies have identified neuronal activity through MEG testing and are able to differentiate between controls and patients with migraine and visual snow.[11] It has been hypothesized that there may be faulty signaling processing in the thalamus, afferent signal of the parietal lobe, or prefrontal lobe of the cerebral cortex. In addition, hyperexcitation of primary and secondary visual cortices, as well as increased saliency of normally ignored subcortical activity, may also contribute to the pathogenesis. BOLD fMRI in patients with visual snow shows reduced activations to visual stimuli in the anterior insular cortices, as well as increased lactate concentrations in the right lingual cortex. This finding supports the idea that dysfunction of the insular cortex in VS could be the cause of a decreased saliency threshold to insignificant stimuli. No structural abnormality has been found in CT and MRI brain studies from patients with visual snow. Visual pathway defects are unlikely since visual snow appears all throughout the visual field and is not confined to a definite axonal pathway. [1]

Primary Prevention

There is no proven prevention or treatment for visual snow. As migraine with aura is a relatively common comorbidity to visual snow, early diagnosis and treatment of migraine with aura may help prevent the development of visual snow, although the two are separate disease processes and no study has documented migraine treatment decreasing the occurrence of visual snow.[7]

Recent developments show that visual snow is triggered by blue short light waves, and ongoing trials will aim to discover if color modulation impacts VS.[12]

Diagnosis

The diagnosis of visual snow is a clinical one made based on a history, normal results from the ophthalmoscopic exam, and a head CT or MRI to rule out other diagnoses.[1] Proposed diagnostic criteria for VS are as follows:

  1. For at least 3 months: dynamic, full-field, tiny dots
  2. Presence of 2 additional visual symptoms:
    1. Palinopsia (afterimage or trailing of moving objects)
    2. Enhanced entopic phenomena (excessive floaters, excessive blue field entoptic phenomena, self-light of the eye, or spontaneous photopsia)
    3. Photophobia
    4. Nyctalopia (impaired night vision)
  3. Symptoms must not be those of typical migraine with visual aura and not explained by another disorder[13]


The table below summarizes the criteria for the definition of visual snow syndrome:

Criteria for the definition of the visual snow syndrome according to Puledda et al [5]

A. Visual snow: dynamic, continuous, tiny dots in the entire visual field lasting >3 mo.

  • The dots are usually black/gray on white background and gray/white on black background; however, they can also be transparent, white flashing, or colored.

B. 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.
    • Afterimages should be different from retinal afterimages, which occur only when staring at a high-contrast Image and are in complementary color.
  • (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, or spontaneous photopsia.
    • Entoptic phenomena arise from the structure of the visual system itself. The blue field entoptic phenomenon is described as uncountable little gray/ white/black dots or rings shooting over the visual field in both eyes when looking at homogeneous bright surfaces such as the blue sky; self-light of the eye is described as colored waves or clouds when closing the eyes in the dark; spontaneous photopsia is characterized by bright flashes of light, kaleidoscope-type colors and spontaneous photopsias[8]
  • (iii) Photophobia.
  • (iv) Nyctalopia.


C. Symptoms are not consistent with typical migraine visual aura.

D. Symptoms are not better explained by another disorder.

  • Normal ophthalmology tests (best corrected visual acuity, dilated fundus examination, visual field, and electroretinogram); not caused by previous intake of psychotropic drugs.


Visual snow may be primary or secondary.[14] It is considered primary when there is no inciting event. Secondary VS is when there is a proven/known secondary cause, such as prior head trauma, hallucinogenic drugs, or other drugs or chronic neurological/ophthalmologic disorder.

Differential Diagnosis

The differential diagnosis for VS includes entopic blue field phenomenon, persistent visual migraine aura, eye floaters, posterior vitreous detachment, retinal detachment, and dyslexia. It is important to distinguish visual snow from other diagnoses, particularly from migraine with aura. A detailed history can distinguish between visual snow and migraine with aura, depending on the frequency and description of the visual changes. Visual snow is constant and specifically has tiny, flickering dots in the visual field, where a patient with migraine with aura will have visual changes that are not constant and will vary in description from that of visual snow. A thorough ophthalmoscopic examination will be able to determine if the patient has a posterior vitreous or retinal detachment perceived by the patient as "floaters."

Patients with dyslexia will also have trouble reading, writing, and concentrating, and the visual change they experience will be described differently, most commonly as letter switching.

Patients with entoptic blue field phenomenon will describe their visual disturbance as black dots with a white tail, seen best against a clear blue sky or another blue background. However, these patients see only a few dots at a time and will not see them over their point of focus, since the phenomenon is caused by white blood cells infiltrating the capillaries of the retina except the foveola.[1]

Physical Examination

The physical examination in VS patients is unremarkable.

Signs

There are no physical signs associated with visual snow.

Symptoms

The symptoms of visual snow include both visual and nonvisual symptoms. Visual symptoms include uncountable, tiny, flickering dots in the visual field; photophobia; visual distortions; contrast problems; decreased clear visual field; decreased depth perception; and palinopsia (prolonged afterimages). Nonvisual symptoms include trouble concentrating, headaches, migraines, irritability, lethargy, and tinnitus.[7][13]

Diagnostic Procedures/Laboratory Tests

Head CT and MRI are commonly ordered to rule out other causes of the visual disturbance, although they appear normal in patients affected by visual snow. The theorized changes in brain parenchyma or neurotransmitters are thought to be extremely localized and thus too small to perceive in any imaging studies. FDG-PET and voxel-based morphometry (VBM) may show hypermetabolism and increased cortical volume in the extrastriate visual cortex at the junction of the right lingual and fusiform gyrus. There are also structural and functional alterations in the occipital lobe supporting the idea that the visual symptoms might be associated with a disturbance in the visual association cortex. [7][13]

Additionally, in further studies, the aberrant central visual processing in VS has been correlated to increased neuronal activity at the lingual gyrus, in the medial temporal lobe by PET, suggesting a "hyperexcitability syndrome." This is the basis of a clinical trial evaluating transcranial stimulation as future treatment of VS.[15]

Management

Because of the nature of this entity, explanation and counseling are essential. Reassurance may be the only treatment needed.

The use of dull colored paper, avoiding bright reading lights, and using a bookmark to decrease line skipping can aid in reading and writing. Tinted glasses lenses have been reported anecdotally to decrease the effects of visual snow, particularly the FL-41 lenses. [16] [17]

Other suggested treatments include meditation and mindfulness, and some studies are further exploring this.

Medical Therapy

Lamotrigine, nortriptyline, carbamazepine, naproxen, topiramate, and sertraline have been reported to decrease symptoms of VS, although they each carry notable side effects and should be reserved for select patients. [13] Lamotrigine led to partial remission of symptoms in 19.6% of patients in one study, but it gave considerable side effects in over 50% of the same patients. [18] The use of pain medication, antiepileptics, and migraine prophylaxis have not been shown to consistently improve the symptoms of visual snow.[7][19]

Surgery

There are currently no surgical options for visual snow.

Prognosis

While visual snow is not usually progressive, it is not known to disappear. Affected patients typically have chronic and recurrent symptoms, but some spontaneously remit or respond to empiric antimigraine or antiseizure treatments.[1]

Additional Resources

References

  1. ↑ Jump up to: 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Fulton, James T., Processes in Biological Vision, Vision Concepts, Corona Del Mar, CA. USA, Aug 2000. Available on the Internet Vision Concepts
  2. ↑ Puledda, Francesca, et al. “Insular and Occipital Changes in Visual Snow Syndrome: a BOLD FMRI and MRS Study.” Annals of Clinical and Translational Neurology, vol. 7, no. 3, 2020, pp. 296–306., doi:10.1002/acn3.50986.
  3. ↑ Jump up to: 3.0 3.1 Solly EJ, Clough M, Foletta P, White OB, Fielding J. The Psychiatric Symptomology of Visual Snow Syndrome. Front Neurol. 2021;12:703006. Published 2021 Jul 30. doi:10.3389/fneur.2021.703006
  4. ↑ Kondziella, D. et al. Prevalence of visual snow syndrome in the UK. Eur. J. Neurol. https://doi.org/ 10.1111/ene.14150 (2020)
  5. ↑ Jump up to: 5.0 5.1 Puledda, Francesca, et al. “Visual Snow Syndrome.” Neurology, vol. 94, no. 6, 2020, doi:10.1212/wnl.0000000000008909.
  6. ↑ Klein A, Schankin CJ. Visual snow syndrome, the spectrum of perceptual disorders, and migraine as a common risk factor: A narrative review. Headache. 2021 Oct;61(9):1306-1313. doi: 10.1111/head.14213. Epub 2021 Sep 27. PMID: 34570907.
  7. ↑ Jump up to: 7.0 7.1 7.2 7.3 7.4 7.5 Schankin, Christoph J, et al., Visual snow: a disorder distinct from persistent migraine aura. A Journal of Neurology, vol. 137, no. 5, May 2014, pp. 1419-1428.
  8. ↑ Jump up to: 8.0 8.1 8.2 Fraser CL. Visual Snow: Updates on Pathology. Curr Neurol Neurosci Rep. 2022 Mar;22(3):209-217. doi: 10.1007/s11910-022-01182-x. Epub 2022 Mar 2. PMID: 35235167; PMCID: PMC8889058.
  9. ↑ Loe, Stephen J., and Kenneth Watson. “A Prospective Genetic Marker of the Visual-Perception Disorder Meares-Irlen Syndrome.” Perceptual and Motor Skills, vol. 114, no. 3, 2012, pp. 870–882., doi:10.2466/24.10.11.27.pms.114.3.870-882.
  10. ↑ Hepschke JL, Seymour RA, He W, et.al. Cortical Oscillatory Dysrhythmias in Visual Snow Syndrome: A MEG Study. bioRxiv 2021.05.17.444460; doi: https://doi.org/10.1101/2021.05.17.444460
  11. ↑ Hepschke JL. Is Visual Snow a thalamo-cortical dysrhythmia of the visual processing system – a magnetoencephalogram study. North American Neuro Ophthalmology Society annual meeting. Amelia Island, FL March 2020.
  12. ↑ Hepschke JL, Martin PR and Fraser CL. Short-Wave Sensitive (“Blue”) Cone Activation Is an Aggravating Factor for Visual Snow SymptomsFront. Neurol., 19 August 2021. https://doi.org/10.3389/fneur.2021.697923
  13. ↑ Jump up to: 13.0 13.1 13.2 13.3 Schankin, Christoph J. et al., Persistent and Repetitive Visual Disturbances in Migraine, A Review. Headache: The Journal of Head and Face Pain, vol. 57, no. 1, July 2016, p.1–16., doi:10.1111/head.12946
  14. ↑ Werner RN, Gustafson JA. Case Report: Visual Snow Syndrome after Repetitive Mild Traumatic Brain Injury. Optom Vis Sci. 2022;99(4):413-416. doi:10.1097/OPX.0000000000001862
  15. ↑ Grande M, Lattanzio L, Buard I, McKendrick AM, Chan YM, Pelak VS. A Study Protocol for an Open-Label Feasibility Treatment Trial of Visual Snow Syndrome With Transcranial Magnetic Stimulation. Front Neurol. 2021 Sep 24;12:724081. doi: 10.3389/fneur.2021.724081. PMID: 34630299; ClinicalTrials.gov Identifier: NCT04925232
  16. ↑ Hale, Alison. My World is not Your World,Revealing Autism, Dyslexic, Scotopic Sensitivity and Asperger Syndrome, 2017 Link
  17. ↑ Axon Optics. What is FL-41. 2017 https://www.axonoptics.com/what-is-fl41/
  18. ↑ Traber, Ghislaine L., et al. “Visual Snow Syndrome.” Current Opinion in Neurology, vol. 33, no. 1, 2020, pp. 74–78, doi:10.1097/wco.0000000000000768
  19. ↑ Vaphiades MS, Grondines B, Cooper K, Gratton S, Doyle J. Diagnostic Evaluation of Visual Snow. Front Neurol. 2021;12:743608. Published 2021 Sep 16. doi:10.3389/fneur.2021.743608
  1. Optics, Axon. Visual Snow Guide. Axon Optics, Mar 2017 Visual Snow Guide
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