Ryanair, at least last year, weren't accepting these from what I saw. As said, too many people using them as an excuse not to wear a mask, and practically no-one ever seems to have an exemption letter when asked for one.

Half of Home Bargains must have been exempt today, yet 100% wearing them in Sainsbury and Tesco before that.

I might claim that my left eye is a fraction better than my right eye, so that makes it a hidden disability as my vision might be 1% worse.