I went to the hospital to have a couple of "probably nothing"s checked today.
Before I saw the doctor a nurse tested my sight with the usual test card (with my usual glasses on). She gave me something to hold onto my nose like specs but 1 side covered. R eye fine. When I turned it round it took a while before I could focus on even the top few lines with the L eye, all the vertical lines were 2 lines. She then hinged up a shutter over the place I'd been looking through, so that instead of a lens hole there were pin-holes. This made it all a lot clearer and I could see down to the line below the red line (the line below that sort of, R eye was a bit better on that line).
So why could I see better through pin-holes than a big hole, and what causes the double lines. Don't remember learning that in physics lessons (a very long time ago)