This thread has lots of good advice, which is nice, but does make me wonder if I am still on NES.
Like lots of people here, I have been dealing with vision issues for quite a while, and I want to talk a bit about "just focus on the blurry sights."
There are actually a number of different ways to see the sights which can work for different types of shooting. The rule to focus on the front sight is necessary for precise target shooting, and is good advice in most situations. But if you can't see the front sight very well, there are other methods.
For close, quick, and coarse work, I focus on the target. Then I bring the gun to position, get a quick blurry view of the sights, and pull the trigger. The overall position and style is similar to two handed point shooting, but with a little bit of sights. This is a method that is taught by some instructors for combat style shooting. So this is similar to just using the blurry sights, but it is more structured.
Note that this method is not for precision work. I can get hits on a 6" circle at 10 yards, or a paper plate a 15 yards, but not much better. But these days, that is about as good as I can do with iron sights anyways. If I think I need real precision, then I use a red dot, and I can get target shooting accuracy if I take my time.