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Although seldom recorded in the medical literature, the ‘visual snow’ phenomenon, as described by patients, leads to a distressing visual condition and often to multiple unnecessary investigations and inappropriate treatments. It impairs daily life, especially through difficulty in reading, focussing and other visual tasks. Medical records of 27 patients were reviewed. They were referred to our neuro-ophthalmic clinic between 2005 and 2010 with unclassified positive visual phenomena. All patients underwent a careful history and complete clinical ophthalmic examination. Most of them had electrophysiology assessment and neuroimaging.
Three of the patients had suffered post-traumatic visual discomfort especially when exposed to bright light, one experienced a phosphene in the central visual field and 23 patients complained of visual snow and/or intrusive after-images without any known precipitant. Among the latter, 20 experienced visual snow, 3 persistent after-images only:
Twenty patients were classified as suffering ‘visual snow’ with or without persistence of after-images. These patients consistently described ‘grainy’, ‘dotty’ or ‘pixelated’ vision affecting the entire visual field of both eyes equally (table 1). The visual experience is likened to ‘television (TV) snow’ or ‘TV noise’ which is the random dot pattern of static displayed when there is no signal on an analoguei TV monitor, hence, the term ‘visual snow’. The symptoms were continuous with some fluctuation, frequently varying with changes in ambient illumination. The …
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