Fear not, actually.
When you say that you have them DVLA will want you to have an eye test, which is utterly logical, so you wait. I assumed it would be at the optician, peripheral vision and all that jazz.
And then after some time they send you a letter to say you will be hearing from your local Driving Test Centre. Eventually you do hear and make an appt. You turn up and the Driving Examiner eventually appears. He checks your details and then you proceed outside, whereupon he tells you where to stand and asks you to read the number plate of that car over there ...... and says if you can't don't worry because where you are standing is a bit long but conveniently situated so if you can't he will measure it exactly (with another car) and you can have another go. And he had one of those big roll up tape measures, with the handle on the side, that they used at school to mark out games pitches etc, tucked under his arm.
It's like deja vu .......
I said don't ask me that silver C4 ! LOL - so he chose another, I said XYZ 123 ..... and they take you back in, fill your form in and fax it back, giving you a photocopy. Think you then have to send a form you have already been sent back to DVLA to say you had it done, but can't recall exactly.
As I see it if you can't read a no plate at 30 paces or whatever it is, well, you shouldn't be driving anyway.
