I believe the cause is entopic phenomena (Google that term and also use the search feature, archives to see previous discussions here). Also look at the topics of discussions threads over the last 5 days. There is a very long post with multiple responses from people that observe the same thing you do.
JCH IIIMD
I went to see my ophthalmologist tonight and I was diagnosed with vitreous condensation in my left eye. My doctor said it should eventually go away and develop into a floater, but that I need to have a follow up visit in three weeks to make sure I doesn't manifest into retinal detachment.
If you haven't already or it hasn't gone away on its own, I recommend having your eye doctor look at it just to be safe.
I was told to watch for flashes in my eye and come in immediately if I did see flashes. I'm not sure if this is happening to you, but if it is then make an appointment right away. Anything that concerns you should be checked by an Opthamologist as soon as possible. It sounds like you are doing that so that is good.
Take care and I hope things work out okay for you.