What Causes Constant Light Flashes And Swirls In Eye?

I see swirls constantly in my left eye. I have very diminished eyesight in that eye. It started with a bright light shining in my eye all of the time then changed to a snow storm and now it is a constant millions of swirls - mostly black and white stripes going in a million directions - swirling, undulating, shifting clockwise and counterclock-wise. I have been tested for macular degeneration, stroke and MS. I have exhibited no symptoms and my CT-scan/MRI was unremarkable. Any suggestion on what this might be?