Welcome Jaz,
I am not a T1D and have no experience with retinopathy, but a friend's husband got it in his forties and I have been sending him links to others with late onset T1D using LowCarb. Maybe you can find answers to your specific questions with these doctors:
Dr. Runyan's own T1D story is here:
http://drkrunyan.com/About.html
and information about his philosophy and practice on the home page. He's in Florida.
Dr. Troy Stapleton has been on a number of LC/Paleo interviews, speaking at seminars, etc. He is on Twitter, etc, and located in Austrialia. Where are you?
http://paleodiabetic.com/tag/dr-troy-stapleton/
I believe that Dr. Bernstein still sees patients in his office (he just turned 80!) and may answer questions by phone if you cannot find it in his book. He also offers TeleSeminars, one coming up on Sept 24th. Certainly the doctor with the most experience using LC to manage T1D.
http://www.diabetes-book.com
And there is a Nephrologist in Toronto Canada recommending a LC diet with IF, more for T2D, but again he is reachable through FB, his blog, and may answer your questions, etc:
http://forum.lowcarber.org/showthread.php?t=461563
Hope you find your answer,