NORD Gratefully acknowledges Dr. Francesca Puledda and Professor Peter James Goadsby, Headache Group, Department of Basic and Clinical Neuroscience, King’s College London, and NIHR-Wellcome Trust King’s Clinical Research Facility, King’s College Hospital, London, UK, for the preparation of this report.

General Discussion

Summary

Visual snow is a neurological disorder characterized by a continuous visual disturbance that occupies the entire visual field and is described as tiny flickering dots that resemble the noise of a detuned analogue television. In addition to the static, or “snow”, affected individuals can experience additional visual symptoms such as visual images that persist or recur after the image has been removed (palinopsia); sensitivity to light (photophobia); visual effects originating from within the eye itself (entoptic phenomena) and impaired night vision (nyctalopia).

The prevalence of visual snow in the general population is currently unknown. The average age of the visual snow population seems to be younger than for many other neurological disorders. This early onset, combined with a general lack of recognition by health care providers, suggest it is an uncommon problem.

Research has been limited because of issues of case identification and diagnosis, the latter now largely addressed, and the limited size of any studied cohort. Initial functional brain imaging research suggests visual snow is a brain disorder.

Visual snow is a chronic condition, sometimes highly disabling, uncommon condition that is in need of collaborative research and lateral thinking to make progress towards understanding, treatment and cure.

Introduction

Since its first description (1), the introduction of the term visual snow (2) and its formal clinical definition less than five years ago (3), visual snow is now being recognized by physicians and scientists as a new entity in the neurological world. The first literature reports of visual snow mostly represented isolated clinical descriptions in the context of larger groups of patients affected by persistent visual disturbance, previously defined as “persistent positive visual phenomena” (1).

Visual snow has been misdiagnosed in case series being mixed with persistent migraine aura, which has led to mechanistic confusion, diagnostic imprecision (4) and certainly the use of treatments that have not been useful (5). Visual snow has been considered to be the same condition as hallucinogen persisting perception disorder (HPPD) (6). Although it seems hallucinogens can trigger a similar disturbance (7), it is clear visual snow syndrome can be entirely independent of drug triggers. Lastly, many patients are told they simply are normal. Admixing these issues has delayed recognition of the syndrome.