Hi I'm Dr Trace -
What it sounds like you are describing is a posterior vitreous detachment. It is a benign condition that occurs as the gel (called the vitreous humor) in the eye softens and moves away from the back of the eye. The area where it contacted the optic nerve is in the shape of a circle - called a Weiss ring. You will see the reflection of light off this under certain lighting conditions and against a white background. Eventually - although it can take many months - the ring will settle down out of your visual axis or your brain will learn to ignore it.
Whenever a person experiences a posterior vitreous detachment, it is a good idea to have a full peripheral retinal examination. In a very small percentage of patients, as the gel begins to move, it can tear a small hole in the retina. This is often associated with flashes of light - like shooting stars - but it may be asymptomatic.
If the examining ophthalmologist were to find a small tear, it is easily treated with a laser in the office. If the tear is ignored however, fluid can seep under the retina and cause a retinal detachment.
So any time you are experiencing symptoms of a posterior vitreous detachment, an ophthalmologist should be consulted.
I hope this answers your question.