It should be a visit to an optometrist. Also check the BP. I can't say for sure, but I seem to remember that if you're having vision issues, and your BP is up, you could be having a stroke. So yeah, do this quickly.
He needs to see an opthamologist as soon as possible. There is an eye forum here that has a eye doctor that might be more helpful. Go to forums and to E and look for eye problems .
You should have his blood sugar levels checked - diabetes affects the sight, and if his blood sugar is high, it may lead to serious medical issues, sight only being one of them!