My grandfather had the very same thing. That's why I protect my eyes from the sunlight, and take Occuvite vitamins. For a while I was eating all the raw spinach I could, and still eat a sprig or two of mint a day. However, if you are talking to your dad, he can still see in his mind's eye any of the glorious things that he HAS seen. If you ask him to remember what it looked like and describe it...it might help. The arrowhead collection can be accessed with his fingers and it might be fun to do that as well. I always considered that if I went blind, I would completely fall in love with "talking books".
Sorry for thread hijacking as well, but it has spurred some thinking about blindness.
My grandfather's blindness deeply depressed him, as he could no longer do woodworking. He could see to get around, but any fine work was beyond him. We tried to be around him as much as possible and get him to tell stories, and he enjoyed that. He's been gone now 10 years...and I miss him every day still. Every time I do a bit of carpentry, plumbing, electrical work, digging, or just tinkering with something trying to fix it or make something new....he's there...whispering in my ear...and I wish he was still here to see all the projects he inspired. My dad was the one that taught me hunting, fishing, baseball, football, and he took up archery when I did...I miss him too. He died in March, and Pap died in August of that same year.