Stripe in vision (similar to after image)

I'm 25. For the past few days I have been seeing a strange dark stripe in my left eye (not in the center, more to the right). It looks like an afterimage after looking into a light or something, except I haven’t looked into anything bright.

I mainly see it on bright surfaces (walls for example) and it only appears when blinking or squinting. If I see it in a darker room, it flashes brightly for a very short moment. I went to the eye doctor three days ago and he dilated my pupils, made a slit lamp examination and an OCT-scan. Nothing wrong with my eyes according to him. Also: It’s definitely not a floater. I have those and they are totally different.

Does anyone have a similar problem?

Edit: I can also see it when moving my eye vertically fast.