I don't know what your kidney function is but I can tell you, my vision seemed pretty bad before I started dialysis. after my very first treatment I felt that I could see better. everything seemed sharper and more in focus.
dirty blood affects your whole body.
diabetes can also play in role in your vision. glad to hear you are maintaining better blood sugar.

I think my eye doctor explained it that when my blood sugar was out of control, there was more fluid in my eye. So when I would get my blood sugar under control, there would be less.

I kept flipping between needing glasses and not needing glasses every other month.

Then after my gastric bypass, my vision stabilized for a year (need glasses).

Now over the last 18 months, it has been a steady decline.

My kidney function has gone up and down over the same period.

I haven't noticed any difference in my vision as my kidney function has declined, but age is definitely a factor (and age and kidney fucntion decline seem to go hand in hand). When your optometrist says 3 levels, that's a signficant change; I've never had a prescription change that much in a decade, let alone a few months.

Before getting new glasses made, you may want to wait a bit and get rechecked by a second optometrist and/or an opthamologist to ensure there's nothing going on inside you eyes beyond simple vision change. Kidney patients, especially those with diabetes (or who had diabetes) are much more prone to eye disease than the general population, so a visit to the opthamologist (MD specializing in eye care) would probably be in order, especially since you've had this continuous decline in a relatively short period of time.

If you're flipping between needing and not needing glasses, you may actually be near and far sighted at the same time (one eye is slightly near sighted, the other slightly far sighted and at each exam a different eye is a bit more dominant). I was a flipper for years on end (but always ended up with 20/20 vision on standard tests) and it wasn't until I was in my mid-30s that an optometrist finally figured out that I my left eye is slightly nearsighted (now more than slightly but still doesn't need glasses per the DMV) and my right eye slightly far sighted. It works great for me; I don't need glasses for anything, but do find them more comfortable for driving (everything is just a bit crisper especially for my left eye) and for reading (eases the strain on the right, far-sighted eye and both eyes in general since my arms aren't long enough to let me read small script, and the standard readers from the grocery store don't work with my unusual prescription).

I hope this helps!
Ruth