jshannon, I am going to have to disagree with the GPS, and I am iffy with the PLB. The GPS, in his situation with limited vision, may not have given him any advantage at all. True, for those of us without a handicap like that, it would have been a great tool (provided one knows how to use it). But, specific to this, is wouldnt have been an asset to him.
The PLB I am on the fence about. Although one can get lost virtually anywhere, the parts of the AT I have trampled are fairly busy, it only being a matter of time before someone finds you (provided you are in close proximinty to the trail). In HIS case, a PLB may have made a difference; in most cases of able bodied hikers on the AT, a PLB is extra weight-and likely wouldnt be carried.
I think a simpler, FAR more effective tool wouldve been the buddy system-you dont necessarily have to walk with the person, but, at certain points, such as side trails, it would be wise to wait & make sure he didnt get lost. The AT is regularly blazed, and quite effectively so; side trails may or may not be. And, the side trail blazings can be literally anything-white triangles, blue squares...or nothing at all. Its up to whoever blazed it. So, its is quite possible he followed, what appeared to him, to be the AT, when in fact it couldve been a side trail.
He is savvy enough to sit & wait it out-he had the gear, and got the patience. My chief concern was him being injured-that couldve had dire consequences. But, it turned out for the best. His years in the woods were to his advantage. Besides, cranky people live longer-we refuse to give in

As a side note, there was a solo hiker a few years back who was completely blind, and he did the whole AT. He hiked alone, but had a dog. There were quite a few people who waited at huts for him nightly, and, by his own admission, he got lost a few times. He made it though. I THINK his name was Bill, but am not 100% sure.