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130 Posts
Dear All
I thought I would try and provide a brief background on the phenomena of visual snow that some people here have reported experiencing and have expressed some concern about. My aim is to provide accurate information that the individual can use and I hope that knowing a little more about the condition may help alleviate some stressful feelings / thoughts. I've used a couple of papers to help compile this - plus some knowledge rattling around my brain. I intend to come back to this post, and provide some questions you can ask yourself about your visual snow experience.
Finally, although I've tried to keep things as non-technical as possible, I also don't believe in patronising anyone here. So some neurological terminology is unavoidable - however, a simple Google will help clarify. If I did this all here - it would make the discussion below far too long.
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Visual snow refers to a condition where the observer experiences excessive 'noise' in the visual system that can be akin to seeing a "television like static" superimposed on the real world. Some researchers have argued for different types of visual snow experience that may reflect different underlying mechanisms. For example, visual snow is typically transparent or achromatic, though it can also be coloured. Generally speaking it appears to reflect some form of spatial 'noise' in the visual system. Perhaps the most common type of visual snow is where the snow is relatively uniform in density over the entire visual field. It can be present in broad daylight, low-light, and even when the eyes are closed. Although the intensity of the snow can be seen to alter over time, it can also be described to be relatively constant and stable. Many patients may become more aware of it in low lighting.
Visual snow (also known as Aeropsia) is classed as a dynamic simple visual hallucination of random form, and as such cannot be classed as being similar to the other types of distortions that patients with DPD/DR experience (i.e., visual distortions or illusions). It arguably has the simplest form of all elementary hallucinations. Visual snow can be transient (particularly if it is associated with Migraine with aura) or permanent (more likely). It can be experienced across the whole field (more typical) or only part of it - like in peripheral vision (rarer).
Additional visual symptoms accompanying visual snow include; Palinopsia (persistence of a visual image after its removal from vision), Entoptic phenomena (specific stimulation), Photophobia (hypersensitivity to light), moving objects leaving trails, excessive floaters, spontaneous photopia, wriggly cell paths (visual worms), and Nyctalopia (impaired night vision). Medication is largely ineffective. Some authors have argued that visual snow can also co-occur with bi-lateral tinitus - though again, this awaits further clarification. It is now regarded that the diagnoses for visual snow is one where it is accompanied by at least 3 other symptoms. Also there is a high prevalence for patients with visual snow to have a history of migraine with aura, visual snow is a distinct clinical entity.
Visual snow is associated with drug intoxication with LSD and mescaline having been associated with its onset. It occurs with HPPD and can be a component of Migraine with aura (known as persistent aura without infarction) though it is distinct from migraine and migraine aura as well. As a consequence, the syndrome of visual snow has been argued to be real and unique. It has been noted to be associated with DPD/DR but few studies on this specific relationship have been carried out to date.
It is suspected that both central (brain) and peripheral (retina / pre-cortical) regions might play a role in the production of visual snow. There is no obvious pathology underlying the experience of visual snow. Visual snow is not a primary eye disease (i.e., the iris, vitreous fluid). However, some are now speculating that it can be linked to cell layers in the retina, or ganglion axons leaving the retina via the optic nerve. In addition, anomalies in the magnocellular portion of the laternal geniculate nuclei (LGN) & superior colliculus (SC) have also been highlighted (these structures are pre-cortical). Aberrant activity due to what is known as parasitic oscillations in certain early (ocular) cells in the visual system - which are then relayed to magnocellular portion of the LGN could be important. One possible candidate generating some excitement at the moment is the condition of, Optic neuritis - which refers to the inflammation of the optic nerve. Recent brain-imaging studies have revealed that the right lingual gyrus is more active in patients with visual snow which strongly suggests it has a neurological (cortical) basis.
Apart from all of the symptoms described above, for patients with DPD/DR there are additional second-order issues (known as secondary sequelae) that can complicate the patient experience further. The existence of visual snow can induce secondary symptoms such as anxiety about main symptoms, stress, panic attacks, depression, hyperreflexivity, and produce an aberrant salience on the symptoms and internal fears. On the downside, people who get visual snow often experience it for their lifetime. On the upside, for many it is not progressive, it gets no worse over the lifetime for most patients.
Useful ref:
Schankin, C.J., (2014). 'Visual snow' - a disorder distinct from persistent migraine aura. Brain, 137, 1419-1428.
Schankin, C.J., et al (2013). Clinical characterization of visual snow (positive persistent visual disturbance). The Journal of Headache and Pain, 14, p132.
I thought I would try and provide a brief background on the phenomena of visual snow that some people here have reported experiencing and have expressed some concern about. My aim is to provide accurate information that the individual can use and I hope that knowing a little more about the condition may help alleviate some stressful feelings / thoughts. I've used a couple of papers to help compile this - plus some knowledge rattling around my brain. I intend to come back to this post, and provide some questions you can ask yourself about your visual snow experience.
Finally, although I've tried to keep things as non-technical as possible, I also don't believe in patronising anyone here. So some neurological terminology is unavoidable - however, a simple Google will help clarify. If I did this all here - it would make the discussion below far too long.
----------------------------------------------------------
Visual snow refers to a condition where the observer experiences excessive 'noise' in the visual system that can be akin to seeing a "television like static" superimposed on the real world. Some researchers have argued for different types of visual snow experience that may reflect different underlying mechanisms. For example, visual snow is typically transparent or achromatic, though it can also be coloured. Generally speaking it appears to reflect some form of spatial 'noise' in the visual system. Perhaps the most common type of visual snow is where the snow is relatively uniform in density over the entire visual field. It can be present in broad daylight, low-light, and even when the eyes are closed. Although the intensity of the snow can be seen to alter over time, it can also be described to be relatively constant and stable. Many patients may become more aware of it in low lighting.
Visual snow (also known as Aeropsia) is classed as a dynamic simple visual hallucination of random form, and as such cannot be classed as being similar to the other types of distortions that patients with DPD/DR experience (i.e., visual distortions or illusions). It arguably has the simplest form of all elementary hallucinations. Visual snow can be transient (particularly if it is associated with Migraine with aura) or permanent (more likely). It can be experienced across the whole field (more typical) or only part of it - like in peripheral vision (rarer).
Additional visual symptoms accompanying visual snow include; Palinopsia (persistence of a visual image after its removal from vision), Entoptic phenomena (specific stimulation), Photophobia (hypersensitivity to light), moving objects leaving trails, excessive floaters, spontaneous photopia, wriggly cell paths (visual worms), and Nyctalopia (impaired night vision). Medication is largely ineffective. Some authors have argued that visual snow can also co-occur with bi-lateral tinitus - though again, this awaits further clarification. It is now regarded that the diagnoses for visual snow is one where it is accompanied by at least 3 other symptoms. Also there is a high prevalence for patients with visual snow to have a history of migraine with aura, visual snow is a distinct clinical entity.
Visual snow is associated with drug intoxication with LSD and mescaline having been associated with its onset. It occurs with HPPD and can be a component of Migraine with aura (known as persistent aura without infarction) though it is distinct from migraine and migraine aura as well. As a consequence, the syndrome of visual snow has been argued to be real and unique. It has been noted to be associated with DPD/DR but few studies on this specific relationship have been carried out to date.
It is suspected that both central (brain) and peripheral (retina / pre-cortical) regions might play a role in the production of visual snow. There is no obvious pathology underlying the experience of visual snow. Visual snow is not a primary eye disease (i.e., the iris, vitreous fluid). However, some are now speculating that it can be linked to cell layers in the retina, or ganglion axons leaving the retina via the optic nerve. In addition, anomalies in the magnocellular portion of the laternal geniculate nuclei (LGN) & superior colliculus (SC) have also been highlighted (these structures are pre-cortical). Aberrant activity due to what is known as parasitic oscillations in certain early (ocular) cells in the visual system - which are then relayed to magnocellular portion of the LGN could be important. One possible candidate generating some excitement at the moment is the condition of, Optic neuritis - which refers to the inflammation of the optic nerve. Recent brain-imaging studies have revealed that the right lingual gyrus is more active in patients with visual snow which strongly suggests it has a neurological (cortical) basis.
Apart from all of the symptoms described above, for patients with DPD/DR there are additional second-order issues (known as secondary sequelae) that can complicate the patient experience further. The existence of visual snow can induce secondary symptoms such as anxiety about main symptoms, stress, panic attacks, depression, hyperreflexivity, and produce an aberrant salience on the symptoms and internal fears. On the downside, people who get visual snow often experience it for their lifetime. On the upside, for many it is not progressive, it gets no worse over the lifetime for most patients.
Useful ref:
Schankin, C.J., (2014). 'Visual snow' - a disorder distinct from persistent migraine aura. Brain, 137, 1419-1428.
Schankin, C.J., et al (2013). Clinical characterization of visual snow (positive persistent visual disturbance). The Journal of Headache and Pain, 14, p132.
which is why you shouldn't listen to some people on these issues. :lol: 
