bakerin,
I'm probably not understanding your medical situation. Have you had any contact with an FAA AME to at least ask what effect your vision would have on getting an FAA medical ?
Rather than wonder, maybe having a chat (without actually taking the physical) with an FAA AME would clear this up for you ? Might be a few dollars well spent.
Enter the search criteria in this website to locate an FAA AME in the UK. I found 22 in the UK:
https://designee.faa.gov/designeeLocator