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C
URRENT
O
PINION
Visual snow syndrome: what we know so far
Francesca Puledda
a
, Christoph Schankin
b
, Kathleen Digre
c
,
and Peter J. Goadsby
a
Purpose of review
We provide an overview of the neurological condition known as visual snow syndrome. Patients affected
by this chronic disorder suffer with a pan-field visual disturbance described as tiny flickering dots, which
resemble the static noise of an untuned television.
Recent findings
The term ‘visual snow’ has only appeared in the medical literature very recently. The clinical features of the
syndrome have now been reasonably described and the pathophysiology has begun to be explored. This
review focuses on what is currently known about visual snow.
Summary
Recent evidence suggests visual snow is a complex neurological syndrome characterized by debilitating
visual symptoms. It is becoming better understood as it is systematically studied. Perhaps the most important
unmet need for the condition is a sufficient understanding of it to generate and test hypotheses about
treatment.
Keywords
palinopsia, persistent visual phenomena, photophobia, visual snow, visual static
INTRODUCTION
Since its first descriptions and clinical definition,
visual snow is increasingly being recognized by
physicians and researchers. The main clinical fea-
ture of the syndrome described consistently by
patients is an unremitting, positive visual phenom-
ena, present in the entire visual field and character-
ized by uncountable tiny flickering dots interposed
between the person’s vision and the background
[1
&&
]. This ‘static’ is typically black and white but
can also be colored, flashing, or transparent. In
addition to the static, or snow, patients can experi-
ence additional visual symptoms of either direct
neurological origin, such as palinopsia, photopho-
bia, and nyctalopia (i.e., impaired night vision), or
that arise from the optic apparatus. This is the case of
entoptic phenomena, a set of different symptoms
commonly found in visual snow syndrome [2],
which may manifest as blue field entoptic phenom-
enon, floaters, self-light of the eye, spontaneous
photopsia, or a combination of those.
The objective of this review is to highlight the
available literature on visual snow to set out what is
known of the clinical picture, pathophysiology, and
available treatments for this hitherto largely unrec-
ognized and disabling condition.
We performed a systematic literature search on
PubMed for any relevant reports and articles on
visual snow up to July 2017; key words were ‘visual
snow’, ‘visual static’, and ‘persistent positive visual
phenomena’.
In the first part we will present a summary of
early literature reports on visual snow (also shown in
Table 1), which mostly represent isolated clinical
descriptions in the context of larger patient groups
affected by persistent visual disturbance attributed
to migraine aura. These reports are an example of
how commonly visual snow can be misdiagnosed as
a form of persistent visual aura, which seems to
share some pathophysiological mechanisms with
the syndrome, even though it clearly represents a
separate disease entity [13].
We will then describe the main findings from
the important studies that have represented the
a
Headache Group, Department of Basic and Clinical Neuroscience,
NIH R-Wellcome Trust King’s Clinical Research Facility, King’s College
Hospital, King’s College London, London, UK,
b
Department of Neurol-
ogy, Bern University Hospital, University of Bern, Bern, Switzerland and
c
Departments of Neurology, Ophthalmology, University of Utah, Salt Lake
City, Utah, USA
Correspondence to Peter J. Goadsby, MD, PhD, Wellcome Foundation
Building, King’s College Hospital, London SE5 9PJ, UK.
Tel: +44 203 299 3106; e-mail: peter.goadsby@kcl.ac.uk
Curr Opin Neurol 2018, 31:52– 58
DOI:10.1097/WCO.0000000000000523
www.co-neurology.com Volume 31 Number 1 February 2018
REVIEW
Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.
initial characterization and definition of the visual
snow syndrome, finally moving onto a detailed
description of the clinical phenotype and main
pathophysiological hypotheses.
THE VISUAL SNOW SYNDROME
Early reports of visual snow
Our reading is that the first clear case report of visual
snow in the literature was by Liu et al. [3]. In this study
10 migraine patients with positive persistent visual
disturbance were grouped in three categories, defined
by the authors on the basis of the relation between the
headache condition and the visual symptoms.
Astutely, three patients, with what can now clearly
be identified as visual snow, were categorized in the
study as study participants for which visual problems
were not necessarily linked with migraine. The
authors noted that even if there was a positive history
for both clinical conditions, there was in fact no
temporal or causal association between the two. It
is interesting to note the personal description of one
study participants symptoms, as ‘snow and flickering
similar to what was between television (TV) chan-
nels’. About 10 years later, Jager et al. [4] was the first
to use the term ‘visual snow phenomenon’ in the
medical literature, describing a possible phenotypic
variant of aura in a study using magnetic resonance
perfusion and diffusion imaging on four patients with
long lasting visual disturbances. Two patients were
defined as having visual snow, and one described her
disturbance as ‘thousands of small yellow, white, or
silvery dots over the whole of both visual fields.’ In
2008 Wang et al. [5] used the Visual Aura Rating Scale
to assess patients with persistent visual disturbance,
and describedtwo study participants with continuous
TV static and noise in their vision or, to use the
patient’s words, ‘tiny black and white dots scattered
throughout the entire visual field.’
The first characterization of visual snow as a
distinct phenomenon was a report in 2013 by Simp-
son et al. [7
&
]. The authors describe the case of a
pediatric patient affected by migrainous headaches
since age 7. The patient presented the sudden onset
of a persistent visual disturbance described as ‘white
bright jagged spots and black and white flashes with
KEY POINTS
Visual snow is a neurological condition characterized
by the presence of a constant pan-field visual
disturbance described as tiny flickering dots that
resemble the noise of a detuned analogue television.
In addition to visual static, patients are affected by
disabling visual symptoms of the type of palinopsia
(afterimages and trailing), entoptic phenomena
(floaters, blue field entoptic phenomenon, photopsia,
self-light of the eye), photophobia, and nyctalopia
forming visual snow syndrome.
At the moment, very little is known about the
pathophysiology of visual snow, as well as possible
treatment strategies for affected patients. Further studies
are necessary to improve our understanding of this
distressing condition.
The review encompasses the published literature on
visual snow, systematically summarizing the key
elements that characterize the phenotype of the
syndrome, as well as what is known so far about its
underlying mechanisms, clinical presentation, and
possible directions for future research on this condition.
Table 1. Studies on visual snow currently published in the literature
Authors Year Name given Patient number Procedure or treatment
Liu et al. [3] 1995 Persistent positive visual phenomena n¼3 Case description
Jager et al. [4] 2005 Primary persistent visual disturbance/
visual snow phenomenon
n¼2 Diffusion and perfusion MRI
Wang et al. [5] and
Chen et al. [6]
2008 Persistent visual aura without infarction n¼2 Case description, visual aura rating
scale, magnetoencephalography
Simpson et al. [7
&
] 2013 Positive persistent visual symptoms/visual
snow
n¼1 Case description
Schankin et al. [1
&&
] 2014 ‘Visual snow’ n¼78 Semistructured telephone interview
Schankin et al. [8
&&
] 2014 ‘Visual snow’ n¼17 [
18
F]-FDG PET
Bessero et al. [9] 2014 ‘Visual snow’ n¼20 Case description
Unal-Cevik and
Yildiz [10]
2015 Visual snow n¼1 Case description, MRI, VEPs,
Lamotrigine treatment
Lauschke et al. [11] 2016 Visual snow n¼32 Case description
McKendrick [12] 2017 Visual snow n¼16 Visual performance tasks
FDG, fludeoxyglucose; VEP, visual evoked potentials.
Visual snow syndrome: what we know so far Puledda et al.
1350-7540 Copyright ß2018 Wolters Kluwer Health, Inc. All rights reserved. www.co-neurology.com 53
Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.
sparkles and dots’ 3 years later. The patient also
reported other key additional symptoms of visual
snow, such as palinopsia and photophobia (see
Fig. 1).
Systematic characterization of the syndrome
These case reports or series, even if isolated and
collected over decades, all described patients com-
plaining of a reasonably homogeneous set of symp-
toms suggesting a unique common syndrome. The
first systematic characterization of patients with
visual snow used a three-step approach [1
&&
]. At first,
a preliminary set of criteria was proposed based on
the reports of 22 patients seen by one of the authors
(P.J.G.), as well as an internet survey completed by
patients with self-assessed visual snow. These crite-
ria were prospectively tested in 78 patients who all
had visual snow, defined as ‘dynamic, continuous,
tiny dots in the entire visual field lasting longer than
3 months.’ About 72 patients (92%) had at least
three additional visual symptoms, supporting the
hypothesis of a clinical syndrome (‘visual snow
syndrome’) and resulting in the proposition of
definitive clinical criteria (Table 2). About one-
fourth of the interviewed patients had symptoms
for as long as they could remember. In the remain-
ing three-fourths, symptom onset was around age 20
and caused an important impact on quality of life.
Most patients had comorbid migraine and many
had typical migraine aura (27%) suggesting an
overlap of disease mechanisms. However, the study
underlined how one of the substantial causes of
distress for patients was the continuing and unre-
mitting symptomatology of visual snow, which
clearly lacks the episodic nature characteristic of
migraine. Moreover, only a minority of study par-
ticipants in the study had visual aura during the
onset of visual snow syndrome, suggesting that
visual snow is different from persistent migraine
aura [1
&&
]. The relation between migraine [9], typical
migraine aura, and visual snow syndrome was fur-
ther studied in 120 patients [8
&&
]. Patients with
visual snow syndrome and concomitant migraine
as a comorbid condition were found to have more
additional symptoms, in particular photophobia,
palinopsia, photopsia, nyctalopia, and tinnitus. In
contrast, such association was not found for comor-
bid migraine aura, which does not alter the typical
phenotype of the visual snow syndrome. These
results seem to suggest that migraine can aggravate
the clinical presentation of the visual snow
syndrome.
Pathophysiological hypotheses
The neurophysiological mechanisms causing visual
snow syndrome are currently unknown. Based on its
clinical description, however, some hypothesis can
be proposed. It is unlikely for a whole-field visual
disturbance to be caused by a disorder of the anterior
retinogeniculate visual pathway, optic radiation, or
FIGURE 1. An original drawing of visual snow made by a 12-year-old patient, clearly showing the visual disturbances of
snow, afterimages (palinopsia), and blue field entoptic phenomena. Reproduced with permission [7
&
].
Neuro-ophthalmology and neuro-otology
54 www.co-neurology.com Volume 31 Number 1 February 2018
Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.
primary visual cortex, which are organized in a
monocular or homonymous fashion; so a simple
disorder of the visual pathway seems less likely.
The additional phenotype of visual snow syndrome
involves palinopsia, that is, the inability to suppress
the just-seen [15] as well as enhanced entoptic phe-
nomena, that is, the inability to suppress the visual-
ization of the optic apparatus [16]. Visual snow
syndrome therefore seems to involve the processing
of visual information in the supplementary visual
cortex, downstream of the primary visual cortex.
This view is supported by the reports of normal eye
examinations and visual evoked potentials (VEP) in
visual snow patients [1
&&
], as well as the results from
the only functional brain imaging study performed
on visual snow [8
&&
]. In this study, involving 17
patients with visual snow syndrome who underwent
[
18
F]-Fludeoxyglucose PET, hypermetabolism of the
lingual gyrus was demonstrated. This area is part of
the supplementary visual cortex and corresponds to
Brodmann area 19. The pathophysiology of visual
snow syndrome might therefore involve dysfunc-
tional visual processing in the lingual gyrus, a theory
also supported by studies on photophobia, a hall-
mark symptom of both visual snow syndrome [1
&&
]
and migraine [14]. Imaging data in fact suggest that
the lingual gyrus is involved in the perception of
photophobia during migraine [17] and furthermore
shows larger cortical thickness in migraineurs when
compared with patients without interictal photo-
phobia [18]. This shared pathophysiology might
thus in part explain the comorbidity of migraine
and visual snow. Further, Brodmann area 19 differs
from other cortical areas with regards to its
microstructure [19]; area 19 extends from the lin-
gual gyrus to other brain areas including V3A, which
is also the region identified as being the earliest to
exhibit functional changes during migraine aura
[20]. This suggests involvement of this structure
in the generation of typical migraine aura and might
be important for the shared pathophysiology of
typical migraine aura and visual snow syndrome.
The question of visual cortical hyperexcitability
in the pathophysiology of visual snow has been
addressed by Chen et al. [6], who studied six patients
with persistent visual disturbance using visual-
evoked magnetic field recording. Two patients
had reported what seemed to be visual snow for
many years, and were found to have a persistent
cortical hyperexcitability, which was inversely cor-
related with disease duration. This suggests that
cortical excitability might differ between patients
with visual snow and those with persistent visual
disturbance of other origin, as is probably also
reflected by the different pharmacological treat-
ment options [21]. In a case report, Unal-Chevik
and Yildiz [10] similarly found a potentiation of
repetitive VEP in a patient with visual snow and
migraine; this alteration normalized after treatment
with lamotrigine in parallel to a clinical improve-
ment. Whether the lack of habituation in these
studies was because of comorbid migraine [22] or
is also a characteristic of visual snow remains an
open question.
In summary, the pathophysiology of visual
snow is unclear, and further studies using strict
criteria and control study participants matched for
migraine and typical migraine aura are necessary to
Table 2. Criteria for the definition of the visual snow syndrome
A Visual snow: dynamic, continuous, tiny dots in the entire visual field lasting longer than 3 months
The dots are usually black/grey on white background and grey/white on black background; however they can also be
transparent, white flashing or colored
B Presence of at least two additional visual symptoms of the four following categories:
(i) Palinopsia. At least one of the following: afterimages or trailing of moving objects. After images 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 one 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 grey/white/black dots or rings shooting over 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
(iii) Photophobia
(iv) Nyctalopia
C Symptoms are not consistent with typical migraine visual aura
As defined by the International Headache Society in the International Classification of Headache Disorders [14]
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 syndrome: what we know so far Puledda et al.
1350-7540 Copyright ß2018 Wolters Kluwer Health, Inc. All rights reserved. www.co-neurology.com 55
Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.
improve our understanding of this distressing con-
dition. The lack of knowledge on the basic biology of
the syndrome leads to the absence of substantially
effective treatment strategies. No clinical and sys-
tematic trials have been performed to date, and all
available data on treatment of visual snow come
from single patients or case reports. The current
evidence seems to show that commonly used med-
ications such as migraine preventives, antidepres-
sants, or pain medication do not consistently
improve or worsen visual snow [1
&&
,23]. There has
been a single positive experience with lamotrigine
[10] and one with naproxen [8
&&
], which however
need be contemplated within their level of evidence.
Differential diagnosis and focus on
associated symptoms
It is important for researchers and clinicians to
distinguish visual snow from other phenomena
and to recognize visual symptoms that can accom-
pany visual snow syndrome. Here we focus on the
associated visual symptoms in visual snow, to facili-
tate its differential diagnosis with other visual
disorders.
When queried [1
&&
], about three-quarters of indi-
viduals with visual snow reported at least three of
four accompanying visual phenomena, of the type
of palinopsia, exaggerated entoptic phenomena,
photophobia, and nyctalopia. These ancillary visual
symptoms were so common in visual snow study
participants that 97% reported more than one addi-
tional symptom and 92% reported up to three.
Palinopsia, also described as the persistence or
continuation of an image after the stimulus is gone
[15], is different from a retinal afterimage, a phe-
nomenon that can commonly be experienced by
healthy individuals [24]. Palinoptic images in visual
snow can manifest as preserved images from station-
ary scenes in over 80% of individuals or as visual
trailing in up to 60% of study participants [1
&&
,2].
Aside from constituting an important manifestation
of the visual snow syndrome, palinopsia can be
seen in neurological diseases with focal lesions
[25], as a side-effect of commonly used preventive
headache medications (e.g., topiramate and acet-
azolamide) [26,27], or as a visual phenomenon in
migraine [28,29].
An exaggerated entopic phenomenon was
reported in 81% of individuals with visual snow.
Entoptic phenomena can be perceived quite com-
monly in the general population, however, the dif-
ference with visual snow patients is that they
perceive them on a daily basis and in a bothersome,
debilitating manner. The eye itself can have reflec-
tive powers and give rise to stimulation of the visual
system, causing the symptoms of entoptic phenom-
ena [16]. One of the most common in the visual
snow syndrome is floaters, the perception of which
is defined as myodesopsia. Floaters are bits and
strands of vitreous that float in the vitreous humor
itself causing stimulation of the retina; they can be
seen best when viewing a white or blue background.
The key feature of floaters is that they move slowly
with changes in gaze and that they are of variable
diameter and brightness.
Some individuals have a keen enough power of
observation to see their own white blood cells flow-
ing within the retinal microvasculature, and can
perceive them as little cells or dots darting around
in a squiggly path, especially when looking at the
blue sky. This phenomenon can be brought out by
using a blue field entoptoscope and is defined
accordingly as the blue field entoptic – or Scheerer’s
– phenomenon [30]. It is present in visual snow in
up to 80% of study participants.
Another important entoptic phenomena pres-
ent in visual snow, which is observed in other eye
diseases, are spontaneous flashes of light, also
known as photopsias. This manifestation, especially
when associated with a sudden increase in floaters
and when more apparent in the dark, can be the
symptom of retinal or vitreal detachment [31]. If
accompanied by glares, shimmering around objects,
visual loss, and night blindness, photopsias can also
be caused by both retinal degeneration and para-
neoplastic retinal degeneration – so-called cancer-
associated retinopathy or melanoma-associated ret-
inopathy syndromes. The keys to not missing the
above diagnoses are a good ophthalmologic exami-
nation – including acuity, visual fields when appro-
priate, and a dilated fundus examination; an
electroretinogram is useful when the diagnosis
remains unclear [32].
Photophobia is very common in migraine, and it
is common in other ocular pathologies; nearly two-
thirds of individuals with visual snow report light
sensitivity as well [1
&&
]. The key characteristic of
photophobia is the avoidance of light, which is
reported by individuals as being either too bright
(photic hypersensitivity) or painful (photic allody-
nia) [33]. It is indeed difficult to assess how much of
the photophobic component of visual snow patients
is actually because of the migraine comorbidity in
these study participants.
Finally, about two-thirds of individuals with
visual snow report nyctalopia. This symptom,
defined as a difficulty seeing at night or in the dark,
can be a sign of retinal degeneration or low vitamin
A. Interestingly, as with all other additional visual
symptoms, nyctalopia is present in the visual
snow syndrome even in study participants with
Neuro-ophthalmology and neuro-otology
56 www.co-neurology.com Volume 31 Number 1 February 2018
Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.
completely normal retinal examinations. Some
patients attribute their reduced night vision to an
increased combination of palinopsia and entoptic
phenomena in low light, whereas others simply
describe the static as being more noticeable with
the absence of other light stimuli, pointing to a
possible dysregulation in the cortical processing of
incoming sensory stimulation.
CONCLUSION
The proposal of a case definition for visual snow has
been reasonably received, and this is a crucial step to
characterize the disorder clinically in large numbers
of study participants and to understand its patho-
physiological mechanisms. The careful collection of
clinical material, and better understanding of the
condition, is essential if progress is to be made
toward developing broadly useful therapeutic
approaches. Furthermore, it is crucial that the dis-
ease be recognized by physicians, particularly by
neurologists and ophthalmologists, who have a
high chance of encountering it in their clinical
practice. This alone would certainly reduce the stress
that most patients deal with in the lengthy quest of
reaching a clear diagnosis for their condition.
Acknowledgements
The authors would like to thank the more than 1000
patients who have contacted the study team in recent
years to take part in research and share their experiences.
It is thanks to their active participation that knowledge
on this condition is being gradually achieved. We would
particularly like to thank the Eye on Vision Foundation,
which is currently active in crowdfunding campaigns to
support the research being conducted on visual snow
syndrome.
Financial support and sponsorship
Work on visual snow conducted by F.P., C.S., and P.J.G.
has been funded by Eye on Vision Foundation, Sierra
Domb, the German Research Foundation, and the Ger-
man Migraine and Headache Society.
K.D. is supported in part by an Unrestricted Grant
from Research to Prevent Blindness, Inc., New York, NY,
to the Department of Ophthalmology and Visual Scien-
ces, University of Utah.
P.J.G. reports grants and personal fees from Aller-
gan, Amgen, and Eli-Lilly and Company; and personal
fees from Akita Biomedical, Alder Biopharmaceuticals,
Avanir Pharma, Cipla Ltd, Dr Reddy’s Laboratories,
eNeura, Electrocore LLC, Novartis, Pfizer Inc, Quest
Diagnostics, Scion, Teva Pharmaceuticals, Trigemina
Inc., Scion; and personal fees from MedicoLegal work,
Journal Watch, Up-to-Date, Massachusetts Medical
Society, Oxford University Press; and in addition, Dr
Goadsby has a patent Magnetic stimulation for headache
assigned to eNeura.
Conflicts of interest
There are no conflicts of interest.
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58 www.co-neurology.com Volume 31 Number 1 February 2018