This overview of Visual Snow Research is presented based on a selection of key articles and findings. A summary is provided at the bottom of the page. References and links are also provided to the articles for those who would like to read more.
Early History of Visual Snow
Initially nothing at all was known about Visual Snow in the clinical setting; patients were describing something and it wasn’t clear how to approach it.
The most popular interpretations were these symptoms were psychogenic (caused by psychological or psychiatric disorders), or that what was being described could be explained by an existing condition such as Migraine with Persistent Aura.
Published early case reports were rare and unfortunately did not immediately create a surge of research interest nor clinical acceptance.
Visual Snow is believed to have been first described in a case report in 1995, as “persistent positive visual phenomena”.
She was involved in a motor vehicle accident, during which she struck another car that crossed in front of her. There was no loss of consciousness or head trauma, but afterwards she saw constant white and black dots, “snow,” and “TV static” over her entire visual field that worsened when she stared at a white background. Later, persistence of visual images (palinopsia) developed. Reading, watching TV, and driving were possible but could be done only with difficulty
A quick internet search can reveal that the term “Visual Snow” started to appear at the turn of the 21st century.
Since that time, I have had visual snow and shimmering problems with my vision (hard to describe – it’s like thousands of points of light moving constantly – make night vision very difficult.. I have trouble reading, etc. my overall vision picture is messed up too
By 2005 the term was also adopted by a group of academics who had begun to notice that similarities between descriptions of “Visual Snow” were noteworthy and suggested a unique underlying condition – deserving its own name and definition.
Having seen a child aged 10 describe exactly the same disturbance of visual snow with blotches as adults, it is hard to believe that there is not a consistent underlying biology that distinguishes this condition.
Visual Snow had had an unclear relationship to migraine and migriane aura. It was important to try and clarify the nature of this relationship.
Persistent visual disturbance is discussed infrequently in the literature; some patients described have a disturbance more like migraine aura than visual snow, and others are not so clear. In these reports, patients frequently have comorbid migraine with or without aura leading to the assumption of visual snow being a migraine- or aura-related condition.
Again, progress on this front was not immediate in initial studies…
We cannot from our negative findings provide biological evidence that these conditions (Visual Snow and Migraine with Persistent Aura) are different but given the very distinct phenotype we feel they would be best studied separately in the future until the position is clearer.
Clinical characterisation of Visual Snow Syndrome
Organised studies however proceeded to look at greater numbers of patients. They increasingly found similarities among groups of patients with Visual Snow, as well as distinctions from migraine and migraine aura. They came to present criteria for the clinical characterisation of a new distinct condition involving Visual Snow (“Visual Snow Syndrome”).
The main criteria for having Visual Snow Syndrome has expanded but is roughly the same since 2012:
#1: “Visual Snow”
Visual Snow is the primary symptom and criteria in Visual Snow Syndrome.
Visual Snow is sometimes described loosely as pixellation or TV static, these descriptions however do not accurately describe Visual Snow.
In the clinical criteria Visual Snow is described in detail as “dynamic, continuous, tiny dots in the entire visual field lasting more than 3 months”.
Every part of that description is important for understanding whether or not you have Visual Snow. It is misunderstanding the distinction between Visual Snow and other visual symptoms which has arguably most contributed to confusion.
These dots are generally black/grey and white but can also be transparent, colored, or white flashing.
#2: An additional associated visual symptom
Visual Snow is almost always associated with additional visual symptoms (
palinopsia, photophobia, “enhanced entoptic phenomena”, nyctalopia), hence “syndrome”.
It’s important to stress that these symptoms themselves do not constitute Visual Snow. Visual Snow is not a collection of symptoms, rather these are symptoms associated with Visual Snow and part of Visual Snow Syndrome.
#3: Symptoms not of opthalmological origin or from drug abuse
Visual Snow being visible in the entire visual field rules out its origin from the eyes.
Furthermore patients with visual snow also tend not to have objective abnormalities on ophthalmologic testing. Other findings have shown that Visual Snow has instead a neurological basis.
You can not be considered to currently have Visual Snow Syndrome if your symptoms were believed to be due to drug abuse. This is because the number of people with Visual Snow who’d taken illicit drugs has appeared very low in clinical studies and such patients may instead be describing similar symptoms from HPPD, which is a different condition.
Research has so far focused on core groups of patients with Visual Snow for research purposes, therefore not fulfilling all the current clinical criteria for Visual Snow Syndrome is not necessarilly an indication that you do not have “Visual Snow”. It means as far as the mainstream research is currently concerned your symptoms may be due to another condition.
This important point about this criteria is mentioned in the video below.
One of the key issues is that control studies such as those on migraine have not yet been carried out on those with HPPD or illicit drug-induced Visual Snow to make any distinctions or overlaps clear. As discussed this has not previously been seen as a core group.
It is possibly not the case however that you cannot have Visual Snow from drug abuse. Another line of research hypothesises that it is possible.
#4: Symptoms not consistent with migraine aura
Although a significant number of those with Visual Snow have been found to experience migraines (~30-60%) and many also have migraine with aura (~27%), notable differences have been found between patients with Visual Snow and control groups.
- Visual Snow does not have an episodic nature
- Visual Snow does not typically start with headache or migraine aura and this was observed as early as in the 1995 case report
- Patients with Visual Snow do not typically respond to migraine medication
- Migrainous visual disturbances do not involve the whole visual field
- Patients with visual snow differ from controls in respect to displaying hypermetabolism in the lingual gyrus (part of the visual cortex). This also provided objective evidence that visual snow was “real”, and had a biological basis.
In the literature of visual snow and persistent migraine aura, some patients were described as having flashing lights, zigzag lines, scintillating scotoma occurring in one visual hemifield or showing directed movement, which have developed with a typical migraine attack. These patients likely have migraine aura and have contributed to confusion over the syndrome
Our data suggest that ‘visual snow’ is a unique visual disturbance clinically distinct from migraine aura that can be disabling for patients. Migraine is a common concomitant although standard migraine treatments are often unhelpful. ‘Visual snow’ should be considered a distinct disorder and systematic studies of its clinical features, biology and treatment responses need to be commenced to begin to understand what has been an almost completely ignored problem.
Those with migraine (but not migraine aura) do however appear to have worse visual snow symptoms and this may be due to a higher susceptability to Visual Snow.
Having migraine results in a worsened visual snow syndrome by being associated with a higher frequency of additional visual symptoms. In contrast, typical migriane aura does not show a correlation suggesting some pathophysiological relevance.
Aspects of migraine pathophysiology may however still be relevant and overlapping with Visual Snow Syndrome.
The lack of association with acute headache attacks or migraine aura episodes initially in visual snow suggests a link to interictal migraine pathophysiology. This is supported by psychophysical studies showing that migraineurs might experience some of the symptoms that are characteristic for visual snow.
Pathophysiology – what is observable and testable when already in a “disease state”.
What mechanisms are behind visual symptoms persisting? If this can be understood then treatment can be suggested.
The majority of hypotheses around pathophysiology have again used migraine theories as a starting point – moving on from the finding of hypermetabolism in the visual cortex (i.e. Cortical Hyperexcitability).
Note that theories may not be mutually exclusive.
Cortical hyperexcitability – too much excitation or too little inhibition in cortical areas of the brain. A theory from migraine research.
Several electrophysiology studies have shown that those with visual snow may have too little inhibition somewhere within the visual cortex and that this pathophysiology is different from control groups.
This study demonstrates robust electrophysiological differences attributed to the processing in the extrastriate visual cortex on the group level in patients with VS. The findings were independent from comorbid migraine or typical migraine aura.
This lack of inhibition may in turn result in a lack of normal sensory adaptation (habituation) to visual stimuli. Instead of normal adaptation, those with visual snow experience the effects of heightened visual responses (potentiation). Some have suggested this means those with Visual Snow see normally sub-threshold stimuli.
Thalamocortical dysrhythmia (TCD) is another theory from migraine research. A TCD is suggested to arise from the excess inhibition of thalamic neurons and inhibitory asymmetry in cortical areas. The thalamic inhibition increases low frequency rhythmicity which can in turn cause a cascade of disruptive events, and excitation in neighbouring cortical parts of the brain.
Because it was found in a study that yellow-blue tinted lenses can subjectively improve some symptoms of visual snow syndrome, TCD was suggested as a possibility within the pathophysiology. Visual stimuli such as yellow tinted lenses selectively activate cells that may cancel or change brain rhythms contributing to a dysrhythmia.
More recently Visual Snow Syndrome has been seen by some as “Sensory Misperception” and a sensory processing disorder. In this way it overlaps not only with migraine but also potentially other disorders.
Noise Within Visual System
Visual Snow is theoretically hypothesised by others to involve neuron(s) that fire inappropriately to add noise into an otherwise normally operating visual system.
At what stage exactly this noise is located, and what role the misfiring neuron(s) plays, may determine the type of noise and therefore static.
A similar conceputal hypothesis for Visual Snow is Stochastic Resonance, which again takes into account additional symptoms such as tinnitus.
Stochastic resonance (SR) is a nonlinear phenomenon where the addition of noise can improve the signal-to-noise ratio, improving the ability to detect a weak stimulus, at least up to an optimal level of noise.
As far as etiology (cause) is concerned there has been little research to date which has attempted to connect possible causes to pathophysiology.
One hypothesis is that a chemical or vascular failure leading to a change in the porosity of tissue in the thalamus or parietal lobe of the brain could be the cause of Visual Snow.
It is of understandable interest to find ways to objectively measure the presence and severity of Visual Snow.
- Saccades – patients with Visual Snow differ from controls in showing a “hyperexcitable stimulus driven response”
- Visual Thresholds – patients with Visual Snow have been found to have an increased threshold for detecting visual contrasts, as well as luminance.
- Hyperexcitability – certain other eletrophysiological measures and neuroimaging of areas such as the visual cortex
Allison M. McKendrick, Yu Man Chan, Melissa Tien, Lynette Millist, Meaghan Clough, Heather Mack, Joanne Fielding, Owen B. White. Behavioral measures of cortical hyperexcitability assessed in people who experience visual snow (2017)
Individual case reports have helped bring attention to Visual Snow and highlight novel cases.
For example, in a recent case report Visual Snow and some associated visual symptoms preceded a variant of Creutzfeldt-Jakob Disease (CJD). This is an interesting case where the authors believe Visual Snow could be one of the first symptoms of a potentially serious underlying brain disease.
It is worth stressing that CJD is a quickly progressing fatal disease and also extremely rare – as such this is an exceptional case (not cause for panic).
Another interesting recent case report documented how a patient was diagnosed with Visual Snow Syndrome and pituitary fatigue and “treated successfully”.
However, despite the diagnosis and interesting hypothesis it’s not actually clear that this person did have Visual Snow. Something which is surprisingly common among case reports.
Unfortunately some case reports are not always viewed critically within a wider context – it is still not uncommon for Visual Snow Syndrome or Visual Snow to be misdiagnosed or misdefined (craziest example) and sometimes conclusions based on individual cases are therefore misleading or in some cases contradictory and lacking validity.
There are general problems with case reports and in particular potential problems with bias in settings such as there are with Visual Snow at the moment.
Case reports and case series can be well received, and have significant influence on subsequent literature and possibly on clinical practice. Many were followed by clinical trials. Often, though, they report rare conditions for which trials may not be feasible, and more or less explicitly transfer established treatment into other conditions. Overall, there is a strong publication bias favoring positive results
There cannot be a discussion about a cure for Visual Snow until it is fully understood what causes it.
As far as treatment goes, so far mainly pharamaceutical drugs have been considered and these have had limited success. The efficacy of treatment approaches has not yet been looked at in any large-scale clinical trials.
There are however ways to adjust to life and health with Visual Snow…
More innovative treatment approaches may also be possible in future.
Visual Snow In Other Languages
Visual Snow research isn’t restricted to the english-speaking world:
Spanish (articles also available in English)
Summary Of Existing Visual Snow Research
- Visual Snow is a symptom, Visual Snow Syndrome is a clinical characterisation of a condition involving Visual Snow.
- Visual Snow Syndrome is a complex neurological condition, not an eye condition.
- Visual Snow Syndrome has specific criteria, although in some cases the symptom of Visual Snow may be mistaken for something else.
- Non-visual symptoms are not currently included within Visual Snow Syndrome criteria.
- Visual Snow Syndrome appears to be distinct from migraine and migraine aura, although there may be a high comorbidity and a useful overlap for research. Patients with migraine may have a susceptibility to visual snow and have worse visual snow symptoms.
- Various hypotheses have been put forward as to the pathophysiology of visual snow and associated symptoms within visual snow syndrome.
- Treatment with existing pharmacological solutions has not been proven.
- There are increasingly ways to objectively test Visual Snow.
- Subjective relief from certain symptoms may be found with the use of tinted lenses, particularly in the yellow-blue colour spectrum.
- More innovative visual snow research is required to further determine etiology, pathophysiology, pathogenesis (progression), as well as treatment possibilities.
- Funding for visual snow research has lately increased.