Visual snow is a symptom described by patients as the continuous perception of tiny flickering dots in the entire field of vision. It has been compared to seeing the world through the static of an out-of-tune analog television. Visual snow is the primary symptom in a cluster of symptoms referred to as visual snow syndrome.
Patients with visual snow syndrome report a set of symptoms, which can include palinopsia (seeing afterimages), entoptic phenomena (increased perception of floaters and other phenomena that arise from the optic apparatus itself), photophobia (sensitivity to light), and nyctalopia (impaired night vision; Brain. 2014;137:1419 http://bit.ly/2mBpnYs).
Despite these symptoms, ophthalmological and neurological exams appear normal. As a result, patients are often misdiagnosed with persistent migraine aura, psychogenic disorders, or malingering (Brain. 2014 http://bit.ly/2mBpnYs).
However, recent research has presented evidence that shows visual snow syndrome is a unique clinical disorder (Brain. 2014 http://bit.ly/2mBpnYs). In addition, it has been shown to be objectively measurable using functional brain-imaging techniques (Headache. 2014;54:957 http://bit.ly/2nAWhtI).
CONNECTION WITH TINNITUS
Three recent studies have shown that approximately 63 percent of patients with confirmed visual snow syndrome also report continuous bilateral tinnitus (Brain. 2014 http://bit.ly/2mBpnYs; Headache. 2014 http://bit.ly/2nAWhtI;J. Clin. Neurosci. 2016;28:123 http://bit.ly/2mBRerb). This high correlation suggests that these conditions may share a common underlying pathophysiology. Several hypotheses for this connection have been suggested.
In 2016, Lauschke et al. proposed that visual snow syndrome may be a thalamocortical dysrhythmia of the visual pathway (J. Clin. Neurosci. 2016 http://bit.ly/2mBRerb). Their results suggest that thalamocortical dysrhythmia may provide a common pathophysiological mechanism connecting visual symptoms with tinnitus and other disorders of sensory processing, a connection that has been previously hypothesized between tinnitus and thalamocortical dysrhythmia (Front. Neurol. 2015; 6:124 http://bit.ly/2nx14zC).
A second hypothesis of interest is predictive coding, which is based on a Bayesian prediction model of the brain. Recent research into predictive coding and tinnitus suggests a common pathophysiology with other positive perceptual disorders (Trends Neurosci. 2016;39:799 http://bit.ly/2niNiA7).
Finally, Zambrowski et al. suggest that visual snow syndrome may result from a “cerebral hypersensitivity,” which leads to the perception of normally sub-threshold physiological phenomena (J Fr Ophtalmol. 2014;37:722 http://bit.ly/2ofgOn7).
In essence, these hypotheses suggest that visual snow syndrome may be to the visual system what tinnitus is to the auditory system (Brain. 2014 http://bit.ly/2mBpnYs).
Additional research studies are under way to further investigate visual snow syndrome, as no known treatment for this condition exists. However, this type of research is very limited and being largely self-funded by individuals with self-assessed visual snow syndrome (Eye On Vision, 2016 http://bit.ly/2nOrol2).
While it is still unknown how visual snow syndrome and tinnitus are related, the high correlation between patients with visual snow syndrome and tinnitus suggests a common underlying pathophysiology. Further research into visual snow syndrome may provide new and interesting insights into tinnitus—insights that may one day lead to rational treatment protocols for both conditions.