Swimming Field of Vision While Meditating?

[Pallero]

I was doing a strong determination sit outiside and looking at a tree branch while I was sitting.

About twenty minutes in something happened. I was focused on one particular leaf on the branch when the edges of my field of vision became blurry, more blurry than usual. A bit like that one Instagram feature that blurs everything but a round area in the center. It was also as though they became less saturated as well.

Then the center area of my field of vision, which was full of leaves, started swimming very slowly.

It looked like a really slow kaleodiscope where when you turn it, areas shift. It wasn's symmetrical like a kaleidoscope though. And it moved very slowly.

Another way to describe it would be like looking on a surface of water where areas of leaves swim in different directions.

My field of vision was made of a few areas that all moved in different directions, sometimes in a spiral. The movement stopped as soon as I tried to look at it straight. It only happened around the leaf that I was focused on. The centre where the leaf was stood still.

I was looking at this for half an hour, before I got a headache.

So. Has anybody had similar experiences? Does this have anything to do with meditation and awareness? Or maybe I should just get my eyes checked and get me some glasses?