The appointment schedule says, "Check Eyes". His owner says, "He was just fine on Friday, and on Saturday he started bumping into things. He falls off the curb, he can't find the steps. I put his treat on the floor and he couldn't find it until I put it up where he could smell it." Well, that sure sounds like he can't see.
When a dog goes gradually blind with age-related cataracts, he becomes accustomed to blurry, ever-worsening vision and learns to compensate. I have had clients whose dogs had been stone-blind for who-knows-how-long and they never knew it until they rearranged the furniture and Fido plowed into the coffee-table. They apparently have a pretty decent quality of life.
When dogs go blind suddenly, they are bumping into everything and they are pretty distressed, just as you would be if somebody suddenly turned out all the lights... permanently (or even just a couple of weeks, as in last year's ice storm aftermath).
So what could make a dog suddenly go blind? He might have a detached retina from trauma or high blood pressure, but that's pretty uncommon. He could have an infection or inflammation in his eye that flared up rapidly. We often see that with Blastomycosis, a systemic fungus that's not uncommon in our area.
OR, he could have cataracts, where the lens inside the eye becomes opaque. This is a close-up of Jackson's eye. I could see his cataracts from across the room -- the pupil of his eye is all white and sparkly. The thing is, cataracts don't usually develop overnight. That is, they don't unless you have Diabetes Mellitus ("sugar diabetes").
"So, Jackson weighs 12 pounds. Has he lost weight?" "He weighed 14 pounds four weeks ago."
"Does he drink a lot of water?" "He is constantly at the water bowl. I can't keep it full."
"How is he feeling? Any vomiting?" "He really doesn't feel good. He doesn't vomit, but he's not eating so well."
And, sure enough, his blood sugar is 434 (should be close to 100), and his urine is full of sugar. Worse, his urine is full of ketones. Without adequate insulin, he has been unable to utilize sugars and starches normally for a long time. So, he has had super-high blood sugar for a long time. This produces the rapid development of cataracts, maybe not totally overnight, but fast. [Check out Veterinary Partner for a more thorough explanation.]
Since he couldn't utilize sugar, he had to break down body fat (and probably some muscle and such, as well), hence the rapid weight loss. Imagine dropping from 140 to 120 in four weeks. This excessive breakdown of fat has produced a lot of the ketone as byproduct. It was making Jackson feel kind of sick. [Here's another link to a diabetes discussion on Veterinary Partner.]
Fortunately, he was still eating (though not well) and not vomiting. Another couple of days and he would have required hospitalization and intensive care. We started him on insulin, and he was already starting to feel a little better the next morning. It will probably take a few weeks to really get him regulated, but he should be enjoying life again pretty soon.