1. I never buy my glasses from them. I felt I got ripped off years ago and learned my lesson.
2. You should ask them to put your "PD" (pupillary distance- distance between your pupils) on your eye prescription. They may charge you a little extra for that ($20-$30?), but it doesn't change and once you have it you have it for new glasses. (Though about anyone you buy glasses from will probably measure it for free, but its good to have a record of it).
3. I go once a year and forgot about the post dilation adventure back into the sunlight. I made a point of writing on my precription "Bring Sunglasses Next Time!!!!!". My doctor's office gives you these flimsy plastic "sunglasses" (below pic), but, handling them makes driving even more challenging.