@acrosstheveil, by 'blurry vision' do you mean that the outline of objects that you are viewing is not as sharp as it should be and feels slightly out of focus?
I have dreadful eyesight and wear glasses. Some days my vision is sharp and other days, quite 'fuzzy around the edges'. I realised that this coincided with how I was doing physically. If I have overdone it and have muscle pain or am having all over PEM, my eyesight is much worse.
My ME affects
all of my muscles, not just skeletal but gut, heart etc. Don't forget that your eyes use tiny muscles when focussing. If you are having even minor issues with other muscles in your body at the same time that you are experiencing blurry vision, it may be worth considering that your eyes could also be having similar problems with fatigue and are simply not working as effectively as they usually do when you are in a better state of health.
I never have my eyes tested when I am feeling bad in case it skews the results and the optician prescribes lenses that would be too strong for me when I am having a good day.
Just my crackpot theory, of course, for what it's worth

!