Visual snow syndrome

Visual snow – the symptom – may sometimes be a transient experience, and it is possible that it is a natural phenomenon, sometimes thought to be visible to many people if they focus on it. In visual snow syndrome, however, visual snow is ever-present, regardless of lighting conditions and even when the eyes are closed. In contrast to visual phenomena caused by migraines, which can last up to about an hour, static caused by visual snow syndrome lasts continuously for several months. However, it is important not to confuse it with other causes of visual snow, which can sometimes manifest as VSS mimics. == Signs and symptoms ==

Visual snow likely represents a clinical continuum, with different degrees of severity. The presence of comorbidities such as migraine and tinnitus are associated with a more severe presentation of visual symptoms. Diagnosis Visual snow syndrome is typically diagnosed with the following proposed criteria: In a 2010 study, Raghaven et al. hypothesize that what the patients see as "snow" is eigengrau. Mimics The following conditions other than visual snow syndrome can also cause visual snow symptoms, and care must be taken not to confuse them with it: • Perceiving visual static, flickering, or graininess on monochrome colors, in the sky, or in darkness can be a normal phenomenon associated with neural noise, amplified in the absence of bright visual stimuli. This effect is related to how the eyes and brain process visual information in low-light conditions. In such environments, the visual system becomes more sensitive to light, amplifying noise or minor changes in visual signals. For example, in low-light conditions, rod photoreceptors, responsible for light perception in dim environments, are primarily activated. However, they cannot distinguish details or colors, leading to a blurred and grainy visual experience without clear contours. Cones, responsible for color perception and detail, are activated in brighter light, while rods provide vision in low-light conditions but with reduced precision. Therefore, the graininess perceived in the dark is a natural adaptation of our vision to photoreceptor limitations, not an indication of abnormality. It's important to note that the perception of such phenomena may vary among individuals due to differences in perception and sensitivity. • Visual noise with closed eyes, also known as phosphenes, refers to the phenomenon where a person perceives random light or dark spots without an external light source. This effect is linked to the ongoing activity of the visual system, even with closed eyes, and can be caused by the electrical activity of neurons in the retina or visual cortex. Studies have shown that the visual system becomes more sensitive when the eyes are closed, which may lead to the perception of phosphenes or visual noise in the dark. These phenomena are a normal part of brain function as it continues processing information in the absence of external stimuli • It is sometimes believed that visual snow syndrome can lead to blindness. This is not true, there are no known cases where this disorder directly led a patient to lose their eyesight entirely. ==Causes==

The causes of VSS are not clear. Persisting visual snow can feature as a leading addition to a migraine complication called persistent aura without infarction, commonly referred to as persistent migraine aura (PMA). In other clinical sub-forms of migraine headache may be absent and the migraine aura may not take the typical form of the zigzagged fortification spectrum (scintillating scotoma), but manifests with a large variety of focal neurological symptoms. ==Recent studies==

• In May 2015, visual snow was described as a persisting positive visual phenomenon distinct from migraine aura in a study by Schankin and Goadsby. • In December 2020, a study found local increases in regional cerebral perfusion in patients with visual snow syndrome. • In September 2021, two studies found white matter alterations in parts of the visual cortex and outside the visual cortex in patients with visual snow syndrome. • In a 2021 study it was found that VSS patients often suffer from anxiety, depression, depersonalization, poor sleep, and fatigue. • In November 2023, a study revealed that glutamate and serotonin are involved in brain connectivity alterations in areas of the visual, salience, and limbic systems in VSS. Importantly, altered serotonergic connectivity is independent of migraine in VSS, and simultaneously comparable to that of migraine with aura, highlighting a shared biology between the disorders. ==Treatments==

It is difficult to resolve visual snow with treatment, but it is possible to reduce symptoms and improve quality of life through treatment, both of the syndrome and its comorbidities. Medications that may be used include lamotrigine, acetazolamide, verapamil, but these do not always result in positive effects. A recent study in the British Journal of Ophthalmology has confirmed that common drug treatments are generally ineffective in visual snow syndrome (VSS). Vitamins and benzodiazepines, however, were shown to be beneficial in some patients and can be considered safe for this condition. It should also be noted that patients should practice caution when seeking out treatment, as research finds that treatment can sometimes have negative effects on existing symptoms or elsewhere. ==References==