I have exactly the same condtion as your dad - only happened to me 3 months ago. It's called a Hemanopia or Hemanopsia. Mine only affects one side, and top/bottom a little - I'm guessing your dad's affected both sides.
I use something like
$1. A large magnifying glass that stands on the table with a movable arm. Good for reading newspapers or magazines
Now this won't be any good to you so close to christmas, but
$1 is fantastic for book reading.
They aren't cheap - but to me at least, they are worth the money. I've always loved reading and couldn't bear to lose the ability to read books.
These might not be much use to you now, but they could be ideas for your dad anyways - I'm sure he'd be over the moon to be able to read again.
Any chance you could list a couple of things or tips your Dad discovered while adjusting? I'm still getting used to it.