I did something similar initially with this model but later decided to add in some pupils. The results were not pretty so I decided that for the first time in over 15 years that I'd try to paint the eyes completely.
It's been a while since I last tried and I had to admit that those intervening decades have taken their toll. Whereas things like first receding then greying hair and increasing weight with decreasing muscle mass are impossible signs of aging for me to ignore, it hadn't really affected my hobby directly (or at least I hadn't admitted it yet). Unfortunately, I've noticed that over the past year or two that my vision has been steadily worsening (I don't need glasses just yet but likely will eventually) and I was having trouble making out smaller details on the models. I'd think that my paint job was good and then cringe at mistakes evident in the mega-zoomed in pics that I'd post here. Since I was putting in the extra effort, I decided to get myself some granny magnifying reading glasses to better see the details as well as finally improve the lighting in the basement where I typically paint as well as buying the smallest technical pens in both white and black that I could find to help with the painting. While far from perfect (too much whites and the asymmetric left iris), I was happy with the results at least at arms length. The general response though was vastly different though.
The above was probalby the best result that I got after repainting the area a half dozen times. After getting feedback on the above, I've done another couple of attempts to fix it with only slightly better results but I'm worried about obliterating the detail on the face if I try again. I toyed with the idea of ripping the head off, stripping it, and restarting from scratch but the results really aren't noticeable at arms length (or even 12" away with my granny glasses) and I think I'll just take the advice given on how to improve it and use it on the next model (likely the upcoming Sister of Battle recently previewed by GW). Regardless, since I was working on it again, I decided to fix the eagle decal that slid up a bit on the shin as well as a few other paint splotches that I missed previously.
For better or worse, that's probably the best that I'll be able to accomplish going forward with the hobby. Looking at the pic, I swear that the dark recess wash goes all the way around the shoulder pad in person but I'll have to double check (and correct that if need be) when I get home tonight.