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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.
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Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.
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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Neuro-ophthalmology and neuro-otology
58 www.co-neurology.com Volume 31 Number 1 February 2018
... Visual snow consists of the appearance of white or black flickering dots in the visual field [47,48]. The disorder may be permanent or transient and does not result from a vision defect. ...
... Some patients refer to the visual symptoms as zigzags, bubbles, or clouds. In this self-described dynamic visual phenomenon, the small flickering dots can be mostly black and white (grey on a black background or black and grey on a white background), but they can also be transparent or coloured [22,34,37,47,48]. The first description in the literature comes from 1995 [49]. ...
... The most popular symptoms are anxiety and depressive disorders [59]. Patients experience derealisation (the belief that the world around them is unreal), depersonalisation (loss of self-identity), or a kind of brain fog [48]. ...
Article
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Visual snow syndrome (VSS) is a rarely diagnosed neurological phenomenon. It is a visual disorder characterised by the presence of numerous white, black, or translucent dots in the visual field, resembling the ‘snow’ of an analogue TV set experiencing reception interference. According to The International Classification of Headache Disorders, 3rd edition, visual snow is defined as a pattern of continuous small dots across the visual field lasting >3 months and accompanied by at least two of the following four additional symptoms: palinopsia, increased entoptic phenomena, photophobia, and nyctalopia. These complaints are not consistent with a typical migraine with visual aura and cannot be better explained by another disorder. The authors present the case of a 39-year-old woman who was diagnosed with VSS. The symptoms appeared after a migraine attack and had not alleviated. The patient reported a sensation of constant ‘TV screen snow’. A neurological examination found no signs of focal damage to the nervous system. The results of the ophthalmological examination, MRI of the brain with contrast, MRI of the eye sockets, and EEG were normal. VSS is a phenomenon that is still not fully understood, different from migraine aura and associated with a number of additional symptoms. VSS is very difficult to treat. In this case, a lot of drugs were used without improvement. Further research must be conducted to determine the best treatment options for these patients.
... The neural origins of visual snow remain unclear and under investigation (e.g., Metzler & Robertson, 2018;Puledda, Schankin, Digre, & Goadsby, 2018;Traber, Aldusary et al., 2020). Based on our conclusion that visual snow is low contrast and contains high temporal frequencies, it is tempting to speculate that it arises along the magnocellular visual pathways. ...
... Longitudinal studies could use matching as an assessment for the effectiveness of treatments, which is currently lacking but necessary for clinical trials . The visual snow simulation could also aid in diagnosis, as it may help distinguish a participant's symptoms from other conditions (e.g., Hang, Leishangthem, & Yan, 2021;Lauschke et al., 2016;Puledda et al., 2018;Yoo et al., 2020). ...
Article
Full-text available
The primary symptom of visual snow syndrome (VSS) is the unremitting perception of small, flickering dots covering the visual field. VSS is a serious but poorly understood condition that can interfere with daily tasks. Several studies have provided qualitative data about the appearance of visual snow, but methods to quantify the symptom are lacking. Here, we developed a task in which participants with VSS adjusted parameters of simulated visual snow on a computer monitor until the simulation matched their internal visual snow. On each trial, participants (n = 31 with VSS) modified the size, density, update speed, and contrast of the simulation. Participants' settings were highly reliable across trials (intraclass correlation coefficients > 0.89), and they reported that the task was effective at stimulating their visual snow. On average, visual snow was very small (less than 2 arcmin in diameter), updated quickly (mean temporal frequency = 18.2 Hz), had low density (mean snow elements vs. background = 2.87%), and had low contrast (average root mean square contrast = 2.56%). Our task provided a quantitative assessment of visual snow percepts, which may help individuals with VSS communicate their experience to others, facilitate assessment of treatment efficacy, and further our understanding of the trajectory of symptoms, as well as the neural origins of VSS.
... Visual snow syndrome is a relatively new medical condition that is characterized as a complex neurological condition with visual symptoms that can be debilitating. [1,2] While the condition was first reported in 1995 [3] as a persistent phenomenon, the terminology of "visual snow" came into vogue 10 years later. [2,4] A patient with visual snow syndrome is said to experience a visual disturbance due to tiny flickering dots in the entire visual field. ...
... The retrieved records were then manually inspected to exclude those with ocular pathology, or with a definitive known ocular diagnosis. Those with unexplained symptoms that matched the existing criteria of visual snow syndrome [1,5,6] were then included, with two exceptions. The exception is that patients were included even if they did not report the symptom of pan field flickering dots, if their other associated symptoms matched the inclusion criteria. ...
Article
Purpose Visual snow syndrome is a debilitating neurological condition. A comprehensive eye examination may not detect any abnormalities in this condition. Presently the condition is recognized only through the history elicited. Hence, it becomes important to understand the presenting complaints and profile of these patients. A retrospective study at a tertiary eye care center was undertaken to achieve this goal. Methods Electronic medical records of patients presenting to a Binocular Vision and Orthoptics clinic were reviewed. Records of the patients containing keywords such as “light sensitivity, shadowing, visual snow, multiple images, and night vision” were retrieved and inspected. Those matching the diagnostic criteria of visual snow syndrome were included in the study. Results A total of 33 patients (average age ± standard deviation: 29.7 ± 9.8 years) were identified. Majority of the patients were males (69%). All the patients had logMAR visual acuity 0 or better in each eye. The most prominent (84.4%) presenting symptom was palinopsia (or afterimage or trailing). About 34.4% complained of floaters (including snow-like appearance). More than half (54.6%) of the patients also had binocular dysfunction. Conclusion Visual snow syndrome is a relatively new condition on the rise, with unclear pathology. The symptoms of this condition can easily be confused with regular floaters or black spots seen in vitreous and retinal pathologies. In the absence of such pathology, an elaborate history should be elicited, and the distress of the patient should be acknowledged. The patient should also be reassured that this is not a blinding condition.
... These findings may support previous hypotheses suggesting closely related mechanisms between tinnitus and migraine and VSS. Earlier hypotheses on the origin of VSS (Fraser 2022) propose that VSS may result from a sensory processing dysfunction leading to incorrect sensory perception (Puledda et al. 2018). ...
Article
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Background: Visual snow syndrome (VSS) is a poorly understood neurological condition of unclear etiology, characterized by visual and non-visual symptoms that reduce quality of life. The objective of our study was to estimate the prevalence of young adults with visual snow in Russia. Materials and methods: We conducted an online survey among 1,177 respondents over the age of 18 residing in Russia. The questionnaire was based on MIDAS, HIT-6, ICHD-3, GAD-7, CES-D. Results: A total of 1085 individuals, divided into three groups: 48 participants with Visual Snow Syndrome (VSS), 36 participants with visual snow symptoms (VS), and 1001 participants without visual snow (control group). Tinnitus (p<0.001) and paresthesia (p<0.001) were more common in participants with VSS compared to the control group. VSS group also reported mood disorders more frequently than those in the other groups (29.2% VSS, 13.9% VS, 7.0% control, p<0.001). Additionally, VSS group exhibited more elevated anxiety levels on the GAD-7 scale compared to the other groups (p=0.005), suggesting a weak association between anxiety and VSS. Conclusions: Diagnosed migraine, tinnitus, concentration problems, paresthesia, and verified psychiatric conditions were significantly more prevalent in the VSS group in our study. Tinnitus was significantly more frequent in the VS group. Diagnosed conditions across all ICD-10 classes were more frequently identified in the VSS group, with the strongest associations (moderate) found with ICD-10 codes: F80-F89 and F60-F69. Additionally ICD-10 codes F30-F39 were more frequently found in the VS group compared to the control group. Our study revealed that nearly all individuals with VSS in our sample (89.6%) had experienced symptoms for as long as they can remember. The prevalence of VS symptoms in Russia is 7.7% (6.2-9.3%) and VSS is 4.4% (3.2-5.7%).
... Table 2 summarizes the number of subjects 144 who marked '4' or '5' on this scale for the symptoms most frequently associated with VSS. The presence 145 of some of these symptoms was a necessary criterion for the diagnosis of VSS (Puledda et al., 2018). 146 ...
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Visual Snow Syndrome (VSS) is characterized by visual perceptual distortions, potentially linked to increased neural excitability. We hypothesized that this hyperexcitability might affect motion direction sensitivity in VSS, particularly in those with trailing-type palinopsia (TTP), an atypical perception of visual motion. Using a spatial suppression paradigm, we assessed motion duration discrimination thresholds for small (1 degrees), medium (2.5 degrees), and large (12 degrees) high-contrast gratings in 23 VSS and 27 control participants. Spatial Suppression Index (SSI) quantified size-dependent increases in duration thresholds. Visual Discomfort Questionnaire scores and VSS symptom ratings including TTP, afterimages, photophobia, etc. were also collected. VSS patients reported higher visual discomfort and perceptual disturbances. However, no group differences were found in duration thresholds or SSI. Notably, higher TTP scores were associated with lower duration thresholds, indicating a facilitatory effect of TTP on motion sensitivity. These findings suggest that 'visual snow,' the core symptom of VSS, is not linked to abnormal directional sensitivity or center-surround suppression associated with visual motion. However, the dependence of directional sensitivity on TTP emphasizes the heterogeneity of VSS, which should be considered in future neurophysiological and clinical models.
... Theoretically, both VSS and tinnitus are different manifestations of a similar process, indicating underlying central mechanisms that may involve aberrant sensory processing within the association cortices or the thalamocortical network [2,13,14]. ...
Article
Full-text available
Background Visual snow (VS) and visual snow syndrome (VSS) are becoming increasingly recognized. However, their prevalence worldwide is unknown. This study aimed to investigate lifetime prevalence and describe the clinical characteristics of VS and VSS in a representative population sample from Italy. Methods This cross‐sectional study was conducted among students attending different faculties in three universities in the central and southern regions of Italy. Eligible participants completed a self‐administered questionnaire. In patients fulfilling possible criteria for VS/VSS, the diagnosis was validated by an on‐site visit conducted by experienced neurologists and neuro‐ophthalmologists that included optical coherence tomography angiography (OCTA). Results A total of 750 participants completed the study. Seven (0.9%) reported symptoms compatible with VS (mean age 24.8 ± 3.85 years). Among the seven patients, five (0.7%) also met the phenomenological and temporal criteria for VSS. Neuroimaging and ophthalmological examinations showed normal results upon review or during the on‐site visit including OCTA. For the five patients with full VSS, the other visual symptoms reported were enhanced entoptic phenomenon (n = 5), photophobia (n = 5), palinopsia (n = 1), and nyctalopia (n = 4). In four of the seven patients (57%) reporting VS symptoms, there was a concomitant diagnosis of migraine with aura, and in one (14%) migraine without aura. All patients (n = 7) reported tinnitus. Six of the seven (85.7%) patients with VS/VSS had never used specific treatments for the condition. None of the seven patients had received a previous diagnosis of VS/VSS. Conclusions The prevalence in Italy of VSS is around 1%. However, there is a limited tendency for affected individuals to seek medical attention, leading to a low rate of diagnosis and treatment.
... A positive visual disturbance known as visual snow syndrome (VSS) [66] has been characterized as the persistent flickering of countless tiny dots throughout the visual field. Alternatively, it is similar to viewing the world through the static noise of an improperly tuned television. ...
Article
Full-text available
Generative artificial intelligence (GAI) can be broadly described as an artificial intelligence system capable of generating images, text, and other media types with human prompts. GAI models like ChatGPT, DALL-E, and Bard have recently caught the attention of industry and academia equally. GAI applications span various industries like art, gaming, fashion, and healthcare. In healthcare, GAI shows promise in medical research, diagnosis, treatment, and patient care and is already making strides in real-world deployments. There has yet to be any detailed study concerning the applications and scope of GAI in healthcare. Addressing this research gap, we explore several applications, real-world scenarios, and limitations of GAI in healthcare. We examine how GAI models like ChatGPT and DALL-E can be leveraged to aid in the applications of medical imaging, drug discovery, personalized patient treatment, medical simulation and training, clinical trial optimization, mental health support, healthcare operations and research, medical chatbots, human movement simulation, and a few more applications. Along with applications, we cover four real-world healthcare scenarios that employ GAI: visual snow syndrome diagnosis, molecular drug optimization, medical education, and dentistry. We also provide an elaborate discussion on seven healthcare-customized LLMs like Med-PaLM, BioGPT, DeepHealth, etc.,Since GAI is still evolving, it poses challenges like the lack of professional expertise in decision making, risk of patient data privacy, issues in integrating with existing healthcare systems, and the problem of data bias which are elaborated on in this work along with several other challenges. We also put forward multiple directions for future research in GAI for healthcare.
... Eren et al. used visual evoked potentials to study patients with VSS compared with control subjects and found that patients with VSS had normal P 100 latencies (corresponding to primary visual cortex) but prolonged N145 latency (corresponding to visual association cortex) [58]. Consistent with this, functional imaging studies of patients with VSS have shown involvement of a variety of brain regions outside of the primary visual cortex [18,49,59,60] One part of the visual cortex, the lingual gyrus, has emerged as a specific area of interest in VSS [1]. Both functional and structural changes in the lingual gyrus have been demonstrated in individuals with VSS [49]. ...
Article
Full-text available
Purpose of Review Visual snow (VS) involves visualization of innumerable dots throughout the visual field, sometimes resembling “TV static.” Patients who experience this symptom may also have additional visual symptoms (e.g., photophobia, palinopsia, floaters, and nyctalopia) with a pattern now defined as visual snow syndrome (VSS). This manuscript describes both VS and VSS in detail and provides an updated review on the clinical features, pathophysiology, and optimal management strategies for these symptoms. Recent Findings VS/VSS may be primary or secondary to a variety of etiologies, including ophthalmologic or brain disorders, systemic disease, and medication/hallucinogen exposure. Evaluation involves ruling out secondary causes and mimics of VS. Increasing evidence suggests that VSS is a widespread process extending beyond the visual system. Pathophysiology may involve cortical hyperexcitability or dysfunctional connectivity of thalamocortical or attention/salience networks. Summary VSS is typically a benign, non-progressive syndrome and can be managed with non-medicine strategies. Though no medication provides complete relief, some may provide partial improvement in severity of VS.
Article
Patients with Visual Snow Syndrome (VSS) experience uncountable flickering tiny dots in the entire visual field. Symptoms often persist over years. Very little is known about altered perception in VSS. VSS is diagnosed based on subjective reports because there is no manual with objective measures. In this study, 20 patients with VSS and 17 healthy controls performed a battery of tests assessing visual acuity, contrast sensitivity, illusion perception, spatial-temporal vision, motion perception, visual attention, and selective attention. Surprisingly, except for one test, the Honeycomb illusion, patients performed at the same level as controls. Patients reporting black and white visual snow performed better in the Stroop test compared to patients reporting other visual snow colors. In addition to a clinical visit, the 30-days clinical diary was administered to patient to broadly measure their symptoms severity. We found that better performance in the tests, and in particular in the contrast and coherent motion tests, correlated with lower VSS symptoms, weaker VS characteristics (e.g., density and size) and lower VS severity. Our results suggest that even if visual abilities are not deteriorated by VSS they can determine how severe symptoms are, and show that VSS is an heterogenous disorder where symptoms and visual abilities vary between patients, for instance depending on the VS color. The study was primarily designed to identify tests where performance differs between controls and patients. In addition, exploratory analyses were conducted to initiate an understanding of the overall pattern of relationships between patients’ visual abilities and symptoms, which is of clinical relevance. Future studies with more power are necessary to validate our findings.
Article
Full-text available
Background: Migraine attacks manifest with hypersensitivities to light, sound, touch and odor. Some people with migraine have photosensitivity between migraine attacks, suggesting persistent alterations in the integrity of brain regions that process light. Although functional neuroimaging studies have shown visual stimulus induced "hyperactivation" of visual cortex regions in migraineurs between attacks, whether photosensitivity is associated with alterations in brain structure is unknown. Methods: Levels of photosensitivity were evaluated using the Photosensitivity Assessment Questionnaire in 48 interictal migraineurs and 48 healthy controls. Vertex-by-vertex measurements of cortical thickness were assessed in 28 people with episodic migraine who had interictal photosensitivity (mean age = 35.0 years, SD = 12.1) and 20 episodic migraine patients without symptoms of interictal photosensitivity (mean age = 36.0 years, SD = 11.4) using a general linear model design. Results: Migraineurs have greater levels of interictal photosensitivity relative to healthy controls. Relative to migraineurs without interictal photosensitivity, migraineurs with interictal photosensitivity have thicker cortex in several brain areas including the right lingual, isthmus cingulate and pericalcarine regions, and the left precentral, postcentral and supramarginal regions. Conclusion: Episodic migraineurs with interictal photosensitivity have greater cortical thickness in the right parietal-occipital and left fronto-parietal regions, suggesting that persistent light sensitivity is associated with underlying structural alterations.
Article
Patients with visual snow suffer from pan-field, dynamic visual disturbance. Proposed diagnostic criteria require at least two additional visual symptoms from: palinopsia, entoptic phenomena, photophobia and nyctalopia. Little is known regarding useful pharmacological treatments for patients. The aim of this study was to gain knowledge on the effect of a number of commonly used medications on visual snow. A questionnaire was prepared in collaboration with the patient group Eye-on-Vision and sent to subjects who had expressed an interest in research. It required to select from a list of drugs, including antiepileptics, antidepressants and benzodiazepines, the treatments that caused a change in symptoms, with either an improvement or a worsening. The study was approved by KCL Research Ethics Panel. For a total of n=182 patients, the effect of ninety-six drugs was recorded in 514 reports. Antidepressants and antiepileptics were the most commonly used drugs; they showed no effect on visual snow in 53% of reports. Visual snow is a highly disabling syndrome, for which there is no widely accepted treatment. More effort needs to be made in understanding its pathophysiology to allow focused treatment strategies.
Article
Patients with visual snow suffer from pan-field, dynamic visual disturbance. Proposed diagnostic criteria require at least two additional visual symptoms from: palinopsia, entoptic phenomena, photophobia and nyctalopia. We characterised patients’ clinical symptoms with regard to the current criteria. An online survey was prepared in collaboration with the patient group Eye-on-Vision. Patients were directed to the site after they contacted us by email asking to be involved in research. The study was approved by the KCL Research Ethics Panel. Of patients (n=514) replying, 280 were male, with a mean cohort age of 29±10 years. They presented with black and white (n=287), coloured (n=222), flashing (n=227) and transparent (n=272) static, with an average of two types of static reported per patient. Floaters (n=446) were the most common associated symptom, followed by afterimages (n=428) and photophobia (n=405). The data confirm earlier work and extend the analysis of the overlapping symptoms. Visual snow can be a highly disabling syndrome that is now becoming better understood as it is recognised and systematically studied.
Article
Objective: To determine whether visual perceptual measures in people who experience visual snow are consistent with an imbalance between inhibition and excitation in visual cortex. Methods: Sixteen patients with visual snow and 18 controls participated. Four visual tasks were included: center-surround contrast matching, luminance increment detection in noise, and global form and global motion coherence thresholds. Neuronal architecture capable of encoding the luminance and contrast stimuli is present within primary visual cortex, whereas the extraction of global motion and form signals requires extrastriate processing. All these tasks have been used previously to investigate the balance between inhibition and excitation within the visual system in both healthy and diseased states. Results: The visual snow group demonstrated reduced center-surround contrast suppression (p = 0.03) and elevated luminance increment thresholds in noise (p = 0.02). Groups did not differ on the global form or global motion task. Conclusion: Our study demonstrates that visual perceptual measures involving the suprathreshold processing of contrast and luminance are abnormal in a group of individuals with visual snow. Our data are consistent with elevated excitability in primary visual cortex; however, further research is required to provide more direct evidence for this proposed mechanism. The ability to measure perceptual differences in visual snow reveals promise for the future development of clinical tests to assist in visual snow diagnosis and possibly a method for quantitatively assaying any benefits of treatments.
Article
Visual disturbances in migraineurs, such as visual aura, are typically episodic, that is, associated with the headache attack, and overlaid by head pain and other symptoms that impact the patient. In some patients, however, visual symptoms are dominant due to frequency (migraine aura status), duration (persistent migraine aura and other persistent positive visual phenomena), or complexity (visual snow syndrome). These syndromes are more rare and challenging to classify in clinical practice resulting in a lack of systematic studies on pathophysiology and treatment. We aim at describing clinical features and pathophysiological concepts of typical migraine aura with a focus on cortical spreading depression and differentiation from non-typical migraine aura. Additionally, we discuss nomenclature and the specifics of migraine aura status, persistent migraine aura, persistent positive visual phenomena, visual snow, and other migrainous visual disturbances. The term migraine with prolonged aura might be a useful bridge between typical aura and persistent aura. Further studies would be necessary to assess whether a return of the classification category eventually helps diagnosing or treating patients more effectively. A practical approach is presented to help the treating physician to assign the correct diagnosis and to choose a medication for treatment that has been successful in case reports of these rare but disabling conditions.
Article
In this paper we review the visual snow (VS) characteristics of a case cohort of 32 patients. History of symptoms and associated co-morbidities, ophthalmic examination, previous investigations and the results of intuitive colourimetry were collected and reviewed. VS symptoms follow a stereotypical description and are strongly associated with palinopsia, migraine and tinnitus, but also tremor. The condition is a chronic one and often results in misdiagnosis with psychiatric disorders or malingering. Colour filters, particularly in the yellow-blue colour spectrum, subjectively reduced symptoms of VS. There is neurobiological evidence for the syndrome of VS that links it with other disorders of visual and sensory processing such as migraine and tinnitus. Colour filters in the blue-yellow spectrum may alter the koniocellular pathway processing, which has a regulatory effect on background electroencephalographic rhythms, and may add weight to the hypothesis that VS is a thalamocortical dysrhythmia of the visual pathway.
Article
This study aims to investigate characteristics of visual snow accompanied by migraine and special interest on occipital bending, electrophysiological properties, and response to treatment. Visual snow is characterized by continuous dynamically flickering dots in the visual field. Most patients also have comorbid migraine. Cortical hyperexcitability is a feature of migraine. Recent studies indicate an association between occipital bending with psychiatric disorders such as depression. Here, we demonstrate a patient with visual snow, migraine with aura, left occipital bending, and cortical hyperexcitability. Treatment response to lamotrigine was objectively assessed by repetitive pattern reversal visual evoked potentials (rVEP). A 25-year-old woman with a 10-year history of migraine with aura (2-3 attacks/week) admitted for 1-year history of visual snow. She reported continuous bright and colorful lights, palinopsia, floaters, nyctalopsia, and photopsia. Brain magnetic resonance imaging (MRI) was performed. Visual habituation response was assessed before and after lamotrigine treatment by rVEP. Brain MRI revealed left occipital bending. On rVEP study, there was potentiation response. After lamotrigine treatment, the patient had no more complaints of visual snow, was able to sleep, and the frequency of migraine decreased to 2 attacks/month. Electrophysiologically, the cortical hyperexcitability was improved. The visual snow and loss of habituation ability in migraine associated with occipital bending can be improved with lamotrigine treatment. This report may provide new insights on "visual snow" pathophysiology in migraine. © 2015 American Headache Society.
Article
To assess the character and cause of photopsias in vitreoretinal patients. Cross-sectional study. A total of 169 consecutive patients (217 eyes) with vitreoretinal disease presenting with a history of photopsias. A total of 217 eyes with photopsias in 169 patients were evaluated. Photopsia assessment included (1) laterality (unilateral, bilateral but not simultaneous, bilateral, and simultaneous); (2) morphology (flash, zig-zag, strobe, scintillating scotoma, twinkling, other); (3) color (white, silver, yellow, combination, other); (4) location (temporal, central, other); (5) duration (quick, prolonged, constant, other); (6) frequency; (7) diurnal appearance (day, night, both); (8) stimuli (turning head or eyes, hypoglycemia, hyperglycemia, other); and (9) associated systemic or ocular signs and symptoms (headache, numbness, weakness, vertigo, syncope, diplopia, hypotension, floaters, other). Clinical photopsia features correlated with the causes of photopsias. Thirty-two photopsia causes were identified. The top 16 included posterior vitreous detachment (PVD) in 39.7% of eyes; retinal tear in 8.9% of eyes; neovascular age-related macular degeneration (AMD) in 7.9% of eyes; rhegmatogenous retinal detachment (RRD) in 7.5% of eyes; classic and ophthalmic migraine in 6.5% of eyes; hypoglycemia in 2.8% of eyes; vertebrobasilar insufficiency in 2.8% of eyes; non-AMD choroidal neovascularization in 2.3% of eyes; retinitis pigmentosa in 1.9% of eyes; severe cough in 1.9% of eyes; central serous chorioretinopathy in 1.4% of eyes; intraocular lens reflections in 0.9% of eyes; blue field entoptic phenomenon in 0.9% of eyes; Charles Bonnet syndrome in 0.9% of eyes; digitalis in 0.9% of eyes; and metastatic adenocarcinoma to the brain in 0.9% of eyes. The photopsias associated with PVD are typically quick (96%), with lightning/flash morphology (96%), white (87%), temporally located (86%), associated with new-onset floaters (85%), preferentially seen in dark (90%) rather than lighted environments (29%), and often initiated by head/eye movements (60%). Retinal detachment had a similar profile, but with more nontemporal photopsias (40%) (P = 0.01). The photopsias from neovascular AMD are more centrally located (83%), quick and repetitive (79%), seen in light (73%) and dark (63%) environments, have no inciting stimuli (84%), and are more likely to be nonwhite (40%). A pointed history for photopsias can reveal a cause that may not initially seem apparent. Thus, the history can play a key role in management decisions. Copyright © 2015 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.