Wow getting glasses because you are borderline, gulp, I have worn glasses since school, did not need them though for driving, technically.
You are missing a lot if you are borderline and do not wear them. Frankly, I would not be seen dead without mine, I am now 68 and my glasses have saved my sight at least 3 times, let alone that I had regular check ups and that was how my glaucoma got picked up.
If, as you say, you are borderline you are being, how can I say this nicely, foolish for not having every advantage that you can get. For example, I can see a bike before you, or a pedestrian. and THAT could mean the difference between life and death. Whereas I can safely drive at say 40 MPH your limit should be 25 or 30.
I am sorry. you should have worn corrective things a lot lot earlier.
I had a UK HGV and now here after 12 years a French HGV and get my medical every year for a bus (although now they want you to do a paper work test every so often but that is the same in the UK although I can still rent one for my private use!) They do a rather mundane test but it does cover everything and I still pass that if I want without correction, (its not put on my licence) but I realise that without glasses I am a liability and I am not borderline by any means!