might sound an bit of an off question but have you seen a different optician?
DD1 is now 8, she used to have coloured lenses because apparently her eye sight was fine (2 opticians said it was fine from 2 different places) and we went to investigate coloured lenses because she was crying from bright lights and reflections. She had letters which were too bold or so pale she couldn't see them, she couldn't see full stops, she was light and contrast sensitive. She also has a lot of dyslexic type problems (and motor planning issues) but ignoring those she had lots of things that we felt something should be able to help. we had tracking tests etc too but all ok.
anyway we got the coloured lenses which helped with contrast and brightness and she "managed" but it still wasn't great.
early last year they gave her a bifocal lense as she was slightly long sighted but had adjustment issues with her focusing (or something - can't say I really remember - bad mum)
anyway late last year we went back for her 6 month check and they suddenly decided she had a slight astigmatism (only small and normally one that they wouldn't actually bother to address I believe). they put that in her glasses along with her slight long sighted prescription and bifocal lenses and suddenly it was like a miracle for her. She now wears her glasses all the time, she can go in shops without finding artificial lighting distorts her vision, she can read with almost no problems (still some dyslexia typc issues but that is separate), she can focus on things, she says she never realised things had straight edges as to her they had always been curved!!!
The opticians were surprised it had made such a huge difference to her.
So now I wonder if whilst the coloured lenses helped but didn't solve the problems was it that she didn't HAVE an astigmatism before, did she just cover it up (she doesn't like to fail tests and is extremely clever and we did suspect she was memorising the sight charts at one point) or should they have seen it was there anyway if it was, I don't even know if you can develop an astigmatism or if you always have it. I had no idea that it could cause all her symptoms but now I have seen the results of having that in her glasses I wish someone had just tried it in the opticians before.
It might be worth discussing with an optician whether astigmatism might be an issue. As I say I don't know anything about it and it might well be they say they have checked and there isn't but it could be that it isn't as clear cut as that and it might be there but not obvious to them yet and your child might be oversensitive to the change like mine.
I am not on here much now so feel free to PM me if you want to.