I would phone gp and ask about the screening test. Not opticians.
My opticians are very good, they contacted the hospital one time because of a problem i have. But they dont do the screening.
Ah ok the reason spec savers need the pin number is because it's used to identify you so that they can claim the fee for retinal screening from the NHS.
Some commissioning groups use opticians for retinal screening rather than hospitals or mobile screening.