One of the benefits of working for a major eyewear manufacturer and retailer is that I get a free pair with all the works every year. I have only worn glasses for about 15 years (I know people that have worn them for much much longer) but in that time I have had a gambit of things go wrong and I have learned from each.
1. When you get your eyes checked for your prescription. If your gut tells you something is wrong, something is wrong. When you look through that machine at near and far when they are done, it should be crystal clear. That means out of each eye, and when looking with both eyes. Garbage in, garbage out. If your prescription is not right, then your glasses will not be right. Dont be afraid to say, can you check that again... my right eye seems off, or they looked good individually but now it seems a bit off..
2. Setting PD has changed considerably over the years. Most places now use a device that they lock to your glasses, and an app on a device that when they line up your picture with that all on your face, it reads the correct place for PD. Unfailingly. It will be accurate.
3. Lenses are not all the same. I get it that the really good lenses (Varilux is one) are expensive. But getting a cheap lens and expecting the best results is the same as buying a cheapo car and expecting it to ride the same as a higher end car. If you get a really inexpensive lens, (especially on progressives) you will probably find your field of view isn't what it could be, or you may find it scratches easier, etc etc.
4. If your glasses aren't right, they aren't right. If your prescription has not changed or has not changed much or you are not new to glasses, then the glasses should be crystal clear when you put them on. If they aren't then:
a. They are either not adjusted correctly on your face.
b. The prescription was not put in the glasses correctly.
c. You are new to glasses (like progressives) and need time to adjust.
d. Your vision has issues and is not stable or your prescription was not accurate.
But with 4 (above), do not be afraid to tell them your glasses are not right. I have had to bring glasses back and have had them re-made. I have also not been happy with a prescription but just lived with it until I get another check (and a different eye doctor) ,only to find the ophthalmologist screwed up. They do make mistakes although its rare. In each of those where I just lived with it, I wish I could go back and say... wait, these arent right!
The difference for me is I get a new pair each year. When I stop w**king, this coming year, I will have to be much more aware when I get new glasses because I will be coming out of pocket. So I have to be my own advocate from one end of the process to the end. If not, I walk around with poor vision until I can afford to get it corrected.
OF course since I know its coming this coming year, I have used my employee discounts to load up on a couple of pair of prescription sunglasses and regular glasses. My prescription has been nice and stable for a few years so that should carry my for a while.