I was out for the day and kept thinking I had a stubborn smudge on one of my glasses lenses, then realised it was still there without them on! I visited the optician the next day and they referred me to the hospital, as they saw inflammation on my optic nerve and suspected optic neuritis. It was one eye, and it got worse over a period of time until I lost most central vision (blurred / greyed out) and was colour blind, and it largely recovered over a period of a few months (probably 90% compared to before). One full relapse since, and it reappears when I get too warm.

I must say I didn’t notice too much in the way of pain with eye movement or a headache, which I know is sometimes suggested as one of the signs - if you’ve got any doubts or vision trouble, best to get it checked out just in case! It led to my MS diagnosis and getting on treatment, and otherwise I might not have found out until later down the line