Cheat Bob … take a 1.5 mm twist drill with you next time you got to a big Tesco , Asda with a chemist kiosk & racks of cheap specs and try a pair of cheapie specs to look at the drill tip . I had several pairs over a period of nearly 10 years ( handy for tying on sea fishing stuff too ) before I had to have proper reading glasses, computer glasses & day/ driving glasses . Even now I still have a couple of pairs of cheapies for when I use my metal lathe or angle grinder & goggles .
Do you think they would mind if I brought in my welding gear so that I can get a pair of specs that give the correct focus at welding distances? My prescription bifocals are ok for reading & everything else but not great when peering through a welding mask!