Dr Sarah Walker-Date
University Hospitals Dorset
Visual snow is a newly recognised condition that presents with debilitating visual symptoms.
Historically, due to the lack of clinical criteria, many patients have been misdiagnosed or had a significant delay in diagnosis. This article is aimed at improving understanding and recognition of visual snow amongst clinicians.
Visual snow was first described in 1995 as continuous snow-like dots or ‘television static’ across the entire visual field (1). It was initially thought to be part of the migraine spectrum or post-concussive syndrome (2). However, patients with no history of migraine or concussions still present with visual snow.
Following this initial report in 1995 there has been increased interest in the condition, and it is now recognised as a distinct disorder with at least 200 cases described in the literature (2).
The underlying aetiology remains unclear. Recent hypotheses suggest abnormal processing of the primary visual cortex and neuronal hyperexcitability (3-4).
The estimated prevalence in the UK is 2% (5).
Visual Snow is a clinical diagnosis made after exclusion of secondary causes such as lesions in the visual field pathway, retinal pathology and neurological diseases (6). Patients should have a full neurological and ophthalmological examination and a CT or MRI head.
Upon excluding secondary causes visual snow can be defined as:
- Continuous and dynamic visual snow present for a minimum of 3 months.
- Plus at least two of the following visual symptoms:
· Entoptic phenomena (visual effects originating within the eye)
· Palinopsia (prolongation of afterimages)
· Nyctalopia (poor vision in low light) (7)
Due to limited understanding of visual snow there is currently no recognised treatment. Recent studies have suggested a possible role of amitriptyline, acetazolamide and lamotrigine in treating visual snow (8,9).
Visual Snow is a recently recognised disease which can have significant effects on patient’s quality of life. This article aims at increasing awareness of the disorder amongst clinicians and highlights an important area for further research, in order to improve our understanding of the aetiology and treatment of this condition.