Large dark circle in the center of my vision?!

Large dark circle in the center of my vision?

I've been noticing a large dark circle in the center of my vision for over a month now. The circle takes up a third or more of my vision. When I close my eyes I see its negative (white). At first I thought it was from staring at something too long, but this morning I had it upon awakening. I thought about it and realised that I've been seeing it a lot lately. Any ideas?

1 month ago
First, I had large black specs in my vision with light around them - went to opthamologist and he couldn't see anything inside my eye to be causing it. This was in the past year. Now I have these dark circles which are NOT really obvious, but I'm starting to notice them more.

1 month ago
Everyone says, "Get to the doctor, get to the doctor". I'm not dumb. I've been going to the doctor(s), but they are not finding anything - that is why I'm asking on Yahoo.

This phenomenon is called a scotoma, and there are many possible causes for it. Anything that causes this kind of vision loss has the potential to be serious, so I would not wait any longer before contacting a physician. Possible causes affect the eye, the optic nerve (which is responsible for vision), or the brain, and may include tumors, progressive neurological diseases, degenerations, infections, etc.