
I had a dog that developed cataracts (though slightly later) and was almost totally blind by the time she was 13. She lived another happy year, almost completely unfazed by her lack of sight, relying on her hearing to not get lost offlead in the fields. I thought about having one cataract removed, but as she was in no discomfort I decided against it.
Dogs don't rely their sight the same way that we do. Their powers of scent and hearing more than compensate, as I learned watching a labrador which had had both eyes removed because of glaucoma sniff out and retrieve fallen game.