This "bad eyesight" thing has been miaquoted out of context, on here and by the media, probably deliberately by the oppo leaders and media.

He said he wanted a short drive to check he was safe (this is a bit strange, I admit) - he then went on to say that he HAD BEEN dizzy with blurry eyesight at the height of his illness.
People have joined up the two statements and the myth that he "drove to test his eyesight" was born.