Sounds like cataracts, which can happen to geese. I had a dewlap toulouse goose born with a rare super aggressive cataract condition that made her completely blind by 6 months old. She had a seeing-eye mate, and we kept her in a small yard with him and a few other disabled birds. She knew every inch of her yard, followed sounds well, and did quite well for six years, when she suddenly passed away for no apparent reason. I am sure your gander knows his home and should transition ok, if you can get him to follow the sound of your voice or shaking a grain bucket.
In my experience, dewlaps do not have long life spans and develop many more issues than other lighter-weight, less ''in bred' breeds. While I have one goose coming 11yo, I am shocked she's still alive. All the rest of my dewlaps seem to pass long before that.
Cherish the time you have. You may get lucky with a few more golden years, but I'm sorry to say you should also be prepared for sudden loss.
