[Aron Stack]

Aron Stack  asked the Naked Scientists:
   
Hello Dr Chris,

I often see purple lights in my vision outdoors at night, I think some people may call them auras but to me they look like any other light at night only purple. They only last for a few seconds and then fade away. I often see the lights when walking at night, and I can see them on buildings, in trees, some times centralised and some times in the corner of vision.

I wondered what the scientific explanation for this phenomenon might be? They don't seem harmful, but I wondered why some people see them.

I have recently had a brain MRI and EEG for unrelated issues which came back clean and also have had an eye test which revealed 20 20 vision.

Thanks

Aron

What do you think?

[RD]

I often see purple lights in my vision outdoors at night ...
 I wondered what the scientific explanation for this phenomenon might be?

Could be phosphenes caused by the movement of your eye flexing your optic nerve...

Phosphenes are brief spots of light brought on by eye movement (movement phosphenes) or sudden noises (sound phosphenes) and which last for less than a couple of seconds. Such phosphenes are often associated with optic neuritis and are caused by mechanical aggravation of a damaged or inflamed optic nerve. They are usually more obvious in low light conditions.

http://www.mult-sclerosis.org/phosphenes.html

I have recently had a brain MRI and EEG for unrelated issues which came back clean and also have had an eye test which revealed 20 20 vision.

Phosphenes can be caused by nerve damage. MRI does not have sufficient resolution* to detect all demyelination, so a "clean" MRI does not necessarily mean "no neurological damage". Nor can MRI detect the presence of small-vessel vasculopathy, (e.g. caused by vasculitis, which can be a cause of optic neuritis). 

*

The recognition, diagnosis and management of cerebral vasculitis ...

imaging by computed tomography or magnetic resonance imaging (MRI) is likewise wholly lacking in sensitivity

http://docs.google.com

Table 1 Cerebral vasculitis: suggested clinical patterns of presentation
which might facilitate recognition (adapted from Scolding et al., 1997)

... Superficially resembling atypical multiple sclerosis (‘MS-plus’) in phenotype – with a relapsing–remitting course and features such as optic neuropathy and brain stem episodes but also accompanied by other features less common in multiple sclerosis – seizures, severe and persisting headaches, encephalopathic episodes or hemispheric stroke-like episodes

http://docs.google.com

[Schmidtzau]

Hi - Did you ever find out the issue with the purple lights you are seeing at night? I had these back in 2006 they lasted about a year, and they went away. They just came back last month 2022. I had MRI, eye check etc.. found nothing. I am just wondering if you ever find anything. Thank you