Oh, and to answer your actual question....
Hypos aren't great for your eyes (or to be accurate, quick changing blood sugars aren't great). Having said that, high blood sugars are probably worse.
They're (possibly, but this is very debatable) not great for your brain in the long term.
Some people lose their hypo awareness if they habitually run their sugars very low. This is the big one, as if you go too low a hypo can actually kill you (but only very rarely, it's more likely that you kill yourself by having an accident when hypo!).