Vision does change of its own accord with time but just to second (well, 3rd or 4th) what everyone else is saying. High BGs distort the actual shape of the eye itself, which naturally changes your vision. Specifically, they cause the eye to swell - not so's you'd notice by looking but enough to change where the light focuses. Before diagnosis when your BGs are higher all the time the eyes and brain adjust to the distortion as "normal" and you don't have the impression of having any vision problems.
Then when you are diagnosed and begin to lower your blood sugars that swelling recedes, so now the shape of your eye is different to what it was before and during the time your eyes and brain adjust to this new normal your vision can actually feel worse - even though it's a sign that you're getting better! This is why - again as has already been said - it's not recommended to get new glasses during the first few months after diagnosis. Your vision is still changing and hasn't settled yet.
Another thing to keep in mind, although it's a little less happy, is that your distance vision may have been getting a bit worse over time, as it tends to do naturally (unrelated to diabetes). Except that the swelling from high BGs would have effectively "covered up" any changes in vision you were having behind the scenes in the meantime. So you may discover that your distance vision is worse than it used to be once your eyes do settle after a few months of stable lower BGs. If that should happen, again nothing to be overly distressed about, it's not caused by diabetes and it's not a sign that something terrible is going to happen to your sight in the future.