I've been wearing bifocals for some time, maybe 10 years. I well remember the first day I went to work wearing them. Those who wear them are familiar with the odd perception thing you get when descending stairs; kind of like you're 10 feet tall.
Well, I had not been at work more than an hour when I get involved in a foot pursuit and the suspect ran down the long flight of stairs that lead down to street level on the North side of campus.
That was an interesting trip! Felt like I was sort of floating....
Caught the guy, though.
Now, I have a pair of "computer" glasses. These are the best thing since sliced bread for the computer user. No more tilting your head backwards to peer through the bifocal. And, a nice no-glare coating that makes the screen appear sharper.