I have a pair of Knobloch glasses, which I bought on ebay for about $100. They included a lens and iris on one eye and a flip up blinder on the other eye.
I bought from Champion's Choice the parts needed to put my reading prescription under the left eye blinder, and had the local optical shop grind the reading lens for the left eye and my distance lens for my right eye.
I find that closing the iris down increases my focus ability on the target A LOT.
Love these glasses, they're worth the money I paid.
Would I shell out the $500 they'd cost new? Probably not, but I am a cheap SOB and I was able to do it for 1/3 that.
If you are focusing on the target, you are not going to progress very far. Most pistol shooters pick their prescription & aperture so they CAN NOT focus on the target. Your mental AND visual focus need to be on the front sight.