Just for general information, in case it happens to someone's pet. I got reminded because of the link I just posted and read someone had a dog that got blind.
Our dog did not feel well and I can't remember why but we took him to the eye vet since he was in town. We found out he was blind in one eye from glaucoma and he had high pressure in both eyes. To us it happened from one day to the next, he was just one evening sluggish.
His other eye we have been able to save with vet's medication (eye drops) now for several years.
Since he was hurting, from pressure, in his blind eye we had it drained, but did not agree to having his eye taken out, to me that was too major surgery.