I find a lot of what people believe are opens or eye issues is really light .... and the lack of use. Fear that comes from having used glass. At least it was for me. So I just painted the pig too.
Vision problems are truely vision problems, but our fore fathers used opens all their lives as it was all they had. There is a psychological crutch that comes from any type of glass that makes you believe that you just HAVE TO have glass. Much as the fear of falling eventually grips older people into using walkers long before it's time. Exercise.
The answer for most of us is light and .... frequency of use. I like opens with more light around the back sight. Larger peeps, wider rear notches. Not as precision on a target, but it works to paint the pig for longer in the day. And surprisingly, I still shoot them fairly well when I try. Just takes a larger, brighter target today than it used to.