What are the medical causes for seeing spots before the eyes?

One possibility is an “optical migraine.” It is a similar mechanism to the migraine in which your head hurts, but affects the blood flow to the eyes.

It can also be an “aura,” a symptom that tells you a migraine is coming.

There are a number of other things that could cause this, too. I suggest you talk to your doctor about it. Some of them can be serious indications that your vision is at risk.

High blood pressure is another possibility.

Are you inquiring about visual snow? There’s a Wikipedia article about it. It is a symptom of colored static in the entirety of one’s vision. I have it all the time and it sucks :(

When I start seeing spots it usually means a migraine is coming. I guess that would be the “aura” Darwin spoke of.

This is what the Rand Eye Institute says. Please read the whole article for the entire list of possible causes. Excerpt:

“It is most probably not your imagination; you are probably experiencing it. Vitreous floaters are usually perceived as spots. The vitreous is the clear liquid that fills the eye. It is jelly-like, almost like clear gelatin.

Without an exam done by your eye care specialist, you cannot know if your floaters or flashes are serious or if they represent any danger to your eye. A significant change in your floaters should alert you to the fact that there has been a change inside your eye. It is wise to have these changes evaluated quickly to safeguard your eyesight.”

I asked a similar question a while back. You might find some of those answers interesting.