ENGLISH
INTRODUCTION
Visual snow (VS) is a rare disorder in neuro-ophthalmology described as the bilateral presence of dynamic, flickering dots covering the entire visual field. Patients often compare it to snow or pixelated television static (Figure 1). Poor recognition of this entity, possibly due to the elusive nature of symptoms, makes it difficult to establish the prevalence of VS.
Figure 1
The patients’ vision was recreated in a photo editing programme. The dense granularity can be seen, corresponding to the pixelated vision of the visual snow patients.
Photo from a private collection. Photo editing program fotocor.com
Additional symptoms can co-occur with VS, both visual and non-visual. Visual symptoms include palinopsia, photophobia, nyctalopia, floaters, spontaneous photopsia, the blue field entopic phenomenon, and self-light of the eye. Among non-visual symptoms, migraines and tinnitus are the most often observed. Visual snow syndrome (VSS) is a separate term, which should not be used interchangeably with VS. It is defined as VS lasting longer than 3 months and being accompanied by at least two, aforementioned additional visual symptoms [1]. According to a survey study in the UK, 2.2% of a representative population sample fulfilled the criteria for VSS [2].
We distinguish two courses of the disease: lifelong and acute onset. In life-long VS, patients claim they have always had it. More troublesome is the acute onset of VS, when the patients are shocked by its sudden occurrence and overwhelmed by the fear of losing their sight. That is the group of patients that seeks help the most, as the condition arouses fear and decreases their quality of life [3].
CASE REPORTS
Patient 1
A 24-year-old woman consulted a neurologist complaining of bright, flickering dots seen with opened and closed eyes, more visible at night and on dark, plain backgrounds but diminished on checked structures or objects. The condition was bothersome while reading paper books and was distracting while studying, aggravated by sleep deprivation, fatigue, and stressful situations. It was accompanied by severe photophobia, nyctalopia, and oscillopsia. Transient photopsia, palinopsia, and tinnitus also occurred (Table I). She has had these symptoms for as long as she can remember. However, only two years ago, after reading a medical article, she realized that her visual symptoms were not physiological and self-diagnosed VS. Therefore, the neurologist referred the patient to an ophthalmologist, and she was admitted to the Ophthalmological Department of Infant Jezus Clinical Hospital in Warsaw.
Table I
VSS-related clinical symptoms
| Clinical symptom | Patient 1 | Patient 2 |
|---|---|---|
| Visual snow | + | + |
| Photophobia | + | – |
| Nyctalopia | + | – |
| Oscillopsia | + | – |
| Transient photopsia | + | – |
| Palinopsia | + | + |
| Tinnitus | + | + |
| Floaters | – | + |
| Scotomas | – | + |
Since age 12, the patient has had psoriasis and is suffering from chronic sinusitis, worsening in autumn and winter. She also mentioned being allergic to dust, grass, birch, and alder.
Since adolescence, the patient has been experiencing dry eyes. Eventually, in 2021, Sjögren’s syndrome was diagnosed. She is currently taking methotrexate at a dose of 15 mg, using moisturizing eyedrops and eye ointment with vitamins A and E.
Furthermore, the patient was diagnosed with fibromyalgia in April 2021. At the same time, she had a COVID-19 infection and experienced a depressive episode. Therefore, cognitive behavioural therapy was suggested to the patient and duloxetine was prescribed at a dose of 120 mg/day. Although the treatment was effective, it aggravated the symptoms of VS. Nevertheless, the patient continued taking the drug.
The patient has no history of migraine headaches.
An extensive ophthalmological examination, including a visual acuity test, fundus examination, intraocular pressure, colour blind test, optical coherent tomography, and corneal topography, was performed. All the results were correct except for low myopia, –0.75 dioptres in both eyes (Table II). According to the patient, wearing eyeglasses with a blue light filter improves her condition.
Table II
Diagnostic tests performed in Department of Ophthalmology, Medical University of Warsaw
In the FLAIR 3D sequence of magnetic resonance of the brain, a couple of very small, unspecific, hyperintense lesions in the frontal lobes were discovered. No pathological enhancement after contrast, limitation of diffusion in diffusion-weighted imaging (DWI), or any other abnormalities were seen. In addition, serum studies and cerebrospinal fluid analysis were normal.
Patient 2
The second patient is her twin sister. She was consulted at an ophthalmology clinic 6 months after her sister. She first noticed VS when she was four years old. Like her sister, she experiences bilateral flashing dots in the visual field with open and closed eyes. Her visual sensation is especially noticeable on a dark background or with closed eyes. Her VS is constant and, according to the patient, is not progressive but intensifies when she is physically and intellectually tired. She states that these symptoms do not diminish her vision quality. Daily, she forgets about having the disorder. It is accompanied by palinopsia, floaters, and scotomas, especially in the morning or after rapidly standing up. Tinnitus also occurs, albeit not frequently, and generally in stressful situations (Table I). The patient also complained of dry eye symptoms but was not diagnosed with disease-causing keratoconjunctivitis.
For as long as she can remember, she has experienced synaesthesia. She associates words, letters, and numbers with colours and music with geometrical shapes or lines.
The patient has a history of migraines recurring monthly, coinciding with menstruation. These migraines can last up to 6 hours and are distressing for the patient. Furthermore, the patient had experienced a migraine aura a few times in her life in the form of a growing scotoma obscuring her vision field.
The patient also has a history of major depression, treated currently with venlafaxine. In adulthood, she was diagnosed with ADHD, treated with methylphenidate, and fibromyalgia. Additionally, she takes metoprolol for anxiety-induced tachycardia and quetiapine for difficulty falling asleep.
She also underwent an ophthalmological examination, including visual acuity tests, fundus examination, intraocular pressure, colour blind test, optical coherent tomography, and corneal topography. All the results were unremarkable except visual acuity, which revealed low myopia, –1.75 dioptres in the left and –2.0 dioptres in the right eye (Table II).
Magnetic resonance of the brain and brainstem with contrast revealed minor, hyperintense lesions in the T2-weighted image in the white matter of the frontal and parietal lobes, which were probably unspecific vascular changes. Early ischemic changes were excluded in DWI. No pathological enhancement after contrast or limitation of diffusion in DWI was discovered. Serum studies and cerebrospinal fluid analysis were normal. She had a positive tetany test.
Diagnosis
Both patients meet the diagnostic criteria of VSS proposed by Schankin et al. [2]. If the onset was rapid, the differential diagnosis would include bilateral optic neuropathies, e.g., methanol intoxication, ischemia, Leber optic neuropathy, and folate/vitamin B12 deficiency, but both of the patients have experienced VS since their childhood. They have no history of taking recreational drugs, which is vital in distinguishing VS from hallucinogen persisting perception disorder (HPPD). Patient 2 has a history of migraine, hardly ever with aura. Even though in migraineurs VS can be present episodically as a part of the aura, and it is possible to confuse these two different conditions, in our patient, the VS is persistent [3].
DISCUSSION
The first criteria for VSS were proposed by Schankin et al. [2]. Both patients fulfilled them as their symptoms had lasted longer than three months, and both had at least two additional symptoms, which are not consistent with typical migraine visual aura and cannot be explained by any other disease. There is no way of diagnosing VSS with an objective examination, so it can only be diagnosed based on the patient’s subjective perception. A questionnaire study on a representative population sample from the UK showed that 2.2% of responders fulfilled the criteria for VSS [1]. Puledda et al. reported that the mean age for onset of VS was 12.8 years, and about 40% of patients had life-long VS [4]. The exact pathophysiology remains unknown. Many different abnormalities have been found in patients with VSS, but none of them had high sensitivity and specificity. In most patients there were no abnormalities in ophthalmologic tests. Structural changes in primary and secondary visual cortices, changes in connectivity in visual, salience and attentional networks and changes in regional cerebral blood flow have been reported. What is more, inconsistent changes in electrophysical and behavioural data have been observed [3]. Both patients suffered from fibromyalgia and tinnitus, supporting the theory that all these diseases may be caused by hypersensitivity to stimuli caused by a sensory network disorder [5].
There is no widely recognized treatment. Information about possible treatment options comes from case reports, case series, and retrospective cohort studies. Prospective studies are very rare. The literature shows that lamotrigine is the most effective drug, helping 22.2% of patients [6], followed by antidepressants, antiepileptics, and benzodiazepines [7]. Recreational drugs and alcohol worsened the symptoms in 9%. Also, atypical antidepressants and ADHD drugs have a high risk of worsening symptoms [8]. It is important to know that only a minority of patients benefit from taking medication. A non-pharmacological approach using yellow-blue colour filters showed improvement in 92% of patients [10]. Unfortunately, there are no more extensive studies assessing their effectiveness in long-term treatment.
Both patients were taking antidepressants, and neither experienced any improvement in VS. One of them was also using methylphenidate, which is said to induce and worsen VS [9].
VSS is a benign condition, but it can mimic more harmful ones. As there are no tests to confirm the diagnosis, it is often misdiagnosed. Occasionally it can be secondary to other diseases. Hang et al. suggested that red flags of secondary VS/VSS are new-onset or intermittent VS, unilateral or quadrant VS, and other ocular or neurological deficits [11]. In acute onset, the differential diagnosis should include bilateral optic neuropathies caused by methanol intoxication, ischemia, Leber optic neuropathy, and folate/vitamin B12 deficiency. Hence, such cases require deepening the diagnostic process, as different symptoms may overlap. For example, in the cases of vasculitis leading to ischemic optic neuropathy, both visual disturbances and headaches co-occur [12, 13]. In migraineurs, VS/VSS can be present, but episodically, as a part of aura. In such cases, VS should not be considered as a separate disorder [12].
It is also vital to take a history of recreational drugs to distinguish VS from another condition that belongs to the VS spectrum – hallucinogen persisting perception disorder (HPPD), which may resemble VSS but has a different mechanism [12].
To our knowledge, there are no other case reports of identical twins suffering from VSS. However, this case may suggest a genetic predisposition in VS, which needs further studies. The main limitation of this case report is the lack of possible treatment for VSS and the lack of follow-up, as no therapeutic intervention has yet been discovered.
CONCLUSIONS
There are no other case reports of identical twins suffering from VSS. The complex etiopathogenesis of VSS requires further ophthalmological and neurological research. This case suggests that a predisposition for VSS may be genetically determined. Visual snow is a rare disorder, and patients may be misunderstood when describing their symptoms. It is necessary to develop a diagnostic procedure that makes it easier for the patient to report symptoms and helps the doctor make a diagnosis.
