I was only recently diagnosed with diabetes but a couple of years ago I got a small blood clot in my right retina, which caused some permanent blurry patches in my vision. At the time I was tested and found not to be diabetic, so they blamed my BP. Now I wonder if that was right...
Anyway, I'm scared too... But that doesn't help. In fact, it makes things worse. Looking after yourself, eating the right things, keeping fit and trying to relax are all useful strategies for getting the best outcome. And there again, plenty of blind people manage to live fun and productive lives - so the worst that can happen isn't the end of everything.
Keep your test appointments and then try not to dwell on negative future possibilities. None of us know what tomorrow will bring, so all we can do is to be as nice as possible to others, and ourselves.