I've already encountered this question about wearing glasses as a photographer. A more specific question I have is as follows. If your eyesight is not perfect, or your glasses and/or contact lenses aren't entirely on point anymore, can you actually determine if focus is sharp, or will you be thrown off target? I was wondering if imperfect eyesight will cause the image in a viewfinder to appear sharp when the lens is actually out of focus, or if there will still be some point of "sharpest focus" when adjusting manually that will appear somewhat blurry to the photographer but is in fact sharp. In other words, is it simply some offset or will bad eyesight never see a sharply focused image?
One thing that I suppose would help greatly is a split prism focus screen, which should make focus clear through alignment, whether it appears perfectly sharp to your eyes or not. Are there other ways?
I often shoot in low light (low enough to make auto-focus unreliable), using film SLRs. None of them has a split prism focus screen and only one has a diopter adjustment. Most of the time I'll be wearing contacts, occasionally glasses. I've noticed my eyes seemed to have deteriorated very slightly the past couple of years, but on the other hand my optician didn't recommend getting my vision as sharp as possible because I work with a computer all day and this would apparently be fatiguing for the eyes. So either I get my prescription changed, learn to compensate focus slightly or find some good trick for this.