Visual snow

Animation showing ripples in the eyes of patients with visual snow syndrome

Visual snow is a form of visual hallucination that is characterized by the perception of small, bilateral, simultaneous, diffuse, mobile (not static), asynchronous points, usually in the entire field of view, but also possible in part. Visual snow is present in all lighting conditions, even with eyes closed. Points remain individual and do not stick together, do not change size. Visual snow exists in one of two forms: impulse type and broadband type. ^[one]

With a pulsed type of visual snow, extraneous points appear in the field of view, like raindrops on a car windshield during very light rain. Dots may be darker or lighter than the background. They may also tend to flicker individually or appear to swirl in sight.

With broadband visual snow, dots appear in the form of a rough texture (similar to the one that is visible on the TV if you turn on the empty channel) with a low amplitude that hides the periphery in the space of objects. Dots may appear to be either lighter or darker than the background.

In rare cases, extraneous points appear different in color. ^[2]

The picture shows the types of visual snow. Two pictures on the left are visual impulse-type snow, two right pictures are visual snow of a broadband type.

Epidemiology

Symptoms of visual snow usually appear during the last years of adolescence and youth. In one study, the average age at which symptoms appeared was 21 years, but visual snow syndrome can occur at any age, both sexes, and in people of any race.

To make sure that a person suffers from visual snow, at least one additional symptom must be noticed in addition to the constant ripples in the eyes. There are times when one symptomatology replaces another. Often patients have many symptoms at the same time. ^[one]

Symptoms of Visual Snow Syndrome ^[3]

• Dynamic, continuous, tiny dots in the entire field of view (noise in the eyes / ripples in the eyes / visual snow / “grain” of the image).
• And at least one additional symptom:
  • Post-image (palynopsia) (visual traces of objects and light from prints of objects);
  • enhanced entoptic phenomena (floats, photopsia , the phenomenon of the entoptic blue field , destruction of the vitreous body , ghostly vision, halo );
  • photophobia (photosensitivity);
  • ringing in the ears ( tinnitus );
  • weakened night vision.
• Symptoms should not differentiate with a typical migraine aura, as well as ophthalmology and drug addiction.

Reasons

The reason for the appearance of visual snow is not known ^[4] . However, at present, visual snow syndrome is considered within the framework of the theory of thalamo-cortical arrhythmias, ^[5] and also suggest that visual snow syndrome is caused by excessive excitability of neurons in the cerebral cortex, in particular, the right lingual gyrus and the left cerebellum of the anterior lobe of the brain. ^[6] Cases of the appearance of visual snow in individuals suffering from a persistent migraine aura and a prolonged perceptual disorder caused by hallucinogens have also been established . ^[7] There is a certain similarity of symptoms with long-term hallucinogen-induced perceptual disturbance (HPPD), but according to studies by Christoph Shankin (MD, University of California, San Francisco), these 2 syndromes are not related.

It is also noted that visual pathway defects are unlikely, since visual snow appears in all fields of view and is not limited to specific axons of the pathway. ^[five]

Risk Factors

Typically, the risks of visual snow syndrome are associated with stress, nonspecific anxiety, dyslexia , autism spectrum disorder , migraines with aura, or the use of recreational and prescription hallucinogens. ^[2]

Diagnostics

Diagnosis of visual snow is based on the patient’s history, normal fundus examination and CT or MRI scans to exclude other diagnoses ^[1] Differential diagnosis of visual snow consists in the exclusion of the following diseases: entopic blue field phenomenon, migraine with aura, vitreous destruction body , retinal detachment, dyslexia .

It is important to distinguish visual snow from other diagnoses, especially migraines with aura. A detailed patient history can help distinguish between visual snow and migraine with aura, depending on the frequency and description of the visual changes. For example, a patient with visual snow constantly and specifically sees tiny, flickering points in the field of view, and a patient with migraine with an aura will see visual distortions that are not constant and will differ from the description of visual snow. A thorough examination of the fundus is also necessary in order to determine whether the patient has ophthalmic disorders, including retinal detachment, which can be perceived by the patient as “floating”. Patients with dyslexia will have problems with reading, writing, and concentration; they will describe the visual changes in different ways. Patients with the blue-field entoptic phenomenon will describe the phenomenon as “visual waves,” “black dots with a white tail,” and also note that this phenomenon is best seen against a clear blue sky or other blue background. ^[one]

Drug Therapy

Medicines that can be used to reduce the symptoms of visual snow: lamotrigine , acetazolamide , verapamil ^[8] , naproxen , nortriptyline, carbamazepine , sertraline ^[9] However, these drugs do not always give a positive effect.

Forecast

Usually visual snow does not progress, but does not disappear. Patients typically have chronic and recurring symptoms. Some patients respond positively to the treatment of migraines with aura or convulsive conditions. ^[one]