I think the point about opticians is a pedantic one about the ones doing the actual tests and prescribing and referring to GPs are the optometrists, not the opticians. But everyone says I'm going to the opticians, and the shop signs usually say opticians. You're probably only going to talk about optometrists if you're getting into a detailed discussion about what you did there and problems it showed.
My opticians is part of PEARS - GPs refer you there for eye checks, because the optometrists there have some kit (and presumably related skills) that other opticians in town don't have. If it's something serious, you then get a hospital referral. Not sure about PEARS, but usually highstreet opticians and audiologists can only write to your GP to ask them to refer you, which seems an unnecessary step.
I went to have my ears microsuctioned at Specsavers, during which we all had a good look at my ear canal on the screen, although I couldn't tell you much about what was going on. They said (and it was they, as they asked for the duty senior audiologist to come and look too, a trained audilogist,) that looks like infection, you need a referral to ENT. GP ignored the letter until I was there for something else a few months later, and asked what's happening. GP agreed it was impacting my hearing - but they only had a handheld otoscope to look, not the choice of kit at Specsavers. Still i got a referral to ENT, which came round quite quickly, and it was ultimately sorted with topical antibiotic drops. But it was an unnecessarily long path to get there, which for me was mildly inconvenient- couldn't hear as well, but for others could have more serious consequences.
If trained optometrists and audiologists could refer directly, it would make more sense, but at the very least, if either the audiologist o'r my GP had said, your GP will also need to see the ear before forwarding on the referral, that would have also helped. I mean, they send me enough messages about flu jab and upcoming appointments, so why not a message to say, we got a letter, please make an appointment.