Visual Snow
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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:
- For at least 3 months: dynamic, full-field, tiny dots
- Presence of 2 additional visual symptoms:
- Palinopsia (afterimage or trailing of moving objects)
- Enhanced entopic phenomena (excessive floaters, excessive blue field entoptic phenomena, self-light of the eye, or spontaneous photopsia)
- Photophobia
- Nyctalopia (impaired night vision)
- Symptoms must not be those of typical migraine with visual aura and not explained by another disorder[13]
Additional information on these criteria is presented by Puledda et al in table 1 in their article in Neurology.[5]
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] 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
- Website that describes a patient with multiple comorbidities: https://www.hale.ndo.co.uk/index.htm
- Simulations of visual snow: https://visionsimulations.com/visual-snow.htm
- Visual Snow Initiative:
- Eye on Vision Foundation
- MBCT-vision mindfulness-based treatment study: https://www.mbct-vision.co.uk/
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Fulton JT. Processes in biological vision. The Complete Neural System. August 2000. https://www.neuronresearch.net/
- ↑ Puledda F, Ffytche D, Lythgoe DJ, et al. Insular and occipital changes in visual snow syndrome: a BOLD fMRI and MRS study. Ann Clin Transl Neurol. 2020;7(3):296-306. doi:10.1002/acn3.50986
- ↑ 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. doi:10.3389/fneur.2021.703006
- ↑ Kondziella D, Olsen MH, Dreier JP. Prevalence of visual snow syndrome in the UK. Eur J Neurol. 2020;27(5):764-772. doi:10.1111/ene.14150
- ↑ 5.0 5.1 Puledda F, Schankin C, Goadsby PJ. Visual snow syndrome. Neurology. 2020;94(6):e564-e574. doi:10.1212/wnl.0000000000008909
- ↑ Klein A, Schankin CJ. Visual snow syndrome, the spectrum of perceptual disorders, and migraine as a common risk factor: a narrative review. Headache. 2021;61(9):1306-1313. doi:10.1111/head.14213
- ↑ 7.0 7.1 7.2 7.3 7.4 7.5 Schankin CJ, Maniyar FH, Digre KB, Goadsby PJ. Visual snow--a disorder distinct from persistent migraine aura. Brain. 2014;137(Pt 5):1419-1428.
- ↑ 8.0 8.1 Fraser CL. Visual snow: updates on pathology. Curr Neurol Neurosci Rep. 2022;22(3):209-217. doi:10.1007/s11910-022-01182-x
- ↑ Loe SJ, Watson K. A prospective genetic marker of the visual-perception disorder Meares-Irlen syndrome. Percept Mot Skills. 2012;114(3):870-882. doi:10.2466/24.10.11.27.pms.114.3.870-882
- ↑ Hepschke JL, Seymour RA, He W, Etchell A, Sowman PF, Fraser CL. Cortical oscillatory dysrhythmias in visual snow syndrome: a MEG study. bioRxiv. Preprint posted online May 18, 2021. doi:10.1101/2021.05.17.444460
- ↑ Hepschke JL. Is visual snow a thalamo-cortical dysrhythmia of the visual processing system? A magnetoencephalogram study. Presented at: Annual Meeting of the North American Neuro-Ophthalmology Society; March 2020; Amelia Island, FL.
- ↑ Hepschke JL, Martin PR, Fraser CL. Short-wave sensitive (“blue”) cone activation is an aggravating factor for visual snow symptoms. Front Neurol. August 18, 2021. doi:10.3389/fneur.2021.697923
- ↑ 13.0 13.1 13.2 13.3 Schankin CJ, Viana M, Goadsby PJ. Persistent and repetitive visual disturbances in migraine: a review. Headache. 2017;57(1):1-16. doi:10.1111/head.12946
- ↑ 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
- ↑ 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;12:724081. doi:10.3389/fneur.2021.724081
- ↑ Hale A. My World Is Not Your World. 2017. https://www.hale.ndo.co.uk/index.htm
- ↑ Axon Optics. What is FL-41. 2017. https://www.axonoptics.com/what-is-fl41/
- ↑ Traber GL, Piccirelli M, Michels L. Visual snow syndrome: a review on diagnosis, pathophysiology, and treatment. Curr Opin Neurol. 2020;33(1):74-78. doi:10.1097/wco.0000000000000768
- ↑ Vaphiades MS, Grondines B, Cooper K, Gratton S, Doyle J. Diagnostic evaluation of visual snow. Front Neurol. 2021;12:743608. doi:10.3389/fneur.2021.743608
- Axon Optics. Visual Snow: Causes, Symptoms, Treatment. March 2017. https://axonoptics.com/blogs/post/visual-snow-guide
