Some Safari pages aren't formatted to allow pinch and zoom. If you need it, turn on three-finger zoom in the Accessibility settings.My eyes are not too good either, and I zoom and swipe when I can. Many pages in Safari won't zoom using the finger pinch. But I have never had a problem as you describe, and don't see how you do it. I'm not disputing you, I just don't see how it happens to you and not me.