Most of the time it's just a floater, condensed vitreous fibrils or a strand
of detached vitreous face turned sideways. They can't always be seen by the
examiner, and you're describing one that is small and pretty close to the
retina.

Floaters don't always "move." But if it sits totally still, it disappears
because your retina quickly adapts and loses perception of it. When you move
your eye, the vitreous jiggles just enough to make the floater detectable.

-MT

Oops, the diagram is wrong. It should be something like:

I
 *  <--the asterisk denotes the center of my right vision field.

I have had a faint line near the center of my field of right vision since
2001. It's not long and I see it _only when_ I move my right eye to the
left. I don't think it's getting longer. And it cannot be a floater because
it doesn't move. When I see it, it looks like this:

\
   *  <--the asterisk denotes the center of my right vision field.

Anyway, a retina specialist examined my right retina yesterday and found no
retinal problem.  So, what could it be?