I know there are a lot of internet resources about visual snow syndrome already out there. I guess I just wanted to add my two cents.
First of all, the proper name of visual snow syndrome is persistent positive visual phenomena distinct from migraine aura. That is just not a handy name to throw around and PPVPDFMA is not easy on the tongue either. So, although the name is in many ways inadequate most people say "visual snow syndrome"
One of the main features of visual snow syndrome is an appearance of snow or TV static in the vision.
Patients who have this symptom know exactly what this means.
It looks like a texture over everything they see.
It usually does not interfere with the true image, but this sensation overlays that image.
There is much more, too...
Patients with visual snow syndrome often describe floaters, seeing lights when their eyes are closed, experiencing after images and visual trails of moving objects.
Some patients even have non-visual symptoms like ringing in the ears.
So, what causes visual snow syndrome?
(First a caution: the research is fairly limited. so we don't actually know all the answers.)
I often use an example of a camera system to explain the visual pathway to patients: The eye is a camera, the optic nerve is a cable and the brain is a computer.
However, that is really quite a poor analogy. In reality the eye is no camera. It is a living organ made up of cells and tissue. Because of this, there is some inherent messiness. There really is stuff floating inside the eye. Everyone has this. Most people are blissfully unaware, but some people are more in tune with their body and they perceive these sensations.
The brain is an organ too. We don't really understand how it works.
If the human brain were so simple
That we could understand it,
We would be so simple
That we couldn’t.
-Emerson M. Pugh
We know that the brain is many, many cells connected in an incredibly complex web.
All those cell do is excite or inhibit each other. Think about that. Every thought you ever had, every memory you can think of, every emotion you ever felt and every sight you ever saw was just a bunch of cells turning off and turning on. Interestingly, the majority of connections in the brain are inhibitory. This means the brain does more work damping things down than actually creating content. I believe that patients with visual snow have less of that inhibition in the visual part of their brain.
So, visual snow is normal visual phenomena, but an increased awareness of it.
Let's repeat that again: Visual snow is normal visual phenomena but an increased awareness of it.
Everything about humanity comes on a spectrum and there is a lot of normal variation within that spectrum. Let's shift to something less abstract for a moment. Let's think about height. Some people are short, some people are tall and everything in between. Despite the difference they are all normal.
So apply that thought to visual perception. Some people are blissfully unaware of the mechanics of their vision. Some people perceive everything their eyes and their occipital cortex is doing. And most people fall somewhere in between.
I teach this condition to medical students and during the lecture I will ask everyone to close their eyes. Then anyone who sees anything other than plain blackness to raise their hands. There are always a couple of hands in the air. Those medical students have a little bit of visual snow syndrome. It may not bother them at all, but it's there.
There are treatments for visual snow. We can use medication like anti-seizure treatments to increase the inhibition of the brain, and sometimes the symptoms will improve. However, there is no medication that works just on the visual part of the brain. If we use medication to inhibit the visual part of the brain, we will probably cause brain fog and other side effects and generally it is not worth it. Most of my patients opt not to treat. (It's not really a disease, but more of a variant of visual experience, so why treat that?) Of the patients who opt to try treatment, almost all end up discontinuing- it is just not worth it.
It is important to understand that this is not a disorder. Many patients are relieved to know this and don't need anything further. Most patients can still function with their visual snow.
I'm not sure if this is true, but I have a feeling that visual snow is a sign of an active mind. My visual snow patients tend to be high functioning and creative people. I wouldn't want to dampen any of that.
In summary, visual snow syndrome is a variant of vision that some people have which is due to increased awareness of normal visual phenomena. Generally, it does not require treatment.