Graham. wrote:
What's the best way of locking them in that won't invalidate
your guarantee from the optician?
Why don't they do this for us?
If I don't tighten the screws on my varifocals on a
weekly basis the RH lens drops out!

You should try the pair that one of my kids has just got.

Lens fell out, screw missing, so I took the specs back to the optician
to sort. They couldn't; transpired they were "unusual" and they had to
send away for parts! Took almost a week.

Less than a week later the same thing happened again, so I took them
back to the optician again in a strop. Turns out they'd got a complete
new duplicate "unusual" pair in previously to sort us out, which meant
that they had one more screw left to fix it the second time.

On closer examination, apparently the way these work is that they have
*two* screws in either side of the lens, one male and one female - like
mini versions of those plastic paired screws which you connect adjacent
kitchen units together with. You have to hold prevent one screw from
rotating using a one slotted jeweller's screwdriver while using a second
screwdriver to turn the head of the other screw 180 degrees opposite
IYSWIM. A *lot* easier said than done, and hardly surprising it's
impossible to nip the bloody screws up tight enough to stop them working
loose. Fab design, huh?

I've told them next time it happens I shall expect a new pair of specs...

David