coke-bottle, generally, refers to thickness. Technically speaking coke-bottle is the effect you get from stong near-sighted...
The coke-bottle tickness for glasses can now be much reduced by using high-densidy (and now even ultra-high-density) glass/plastics which have a (much) higher than normal refraction index, The higher refraction index means that you don't need as sharp a curve (and, thus thickness) to achieve the needed focus correction.
A you get older, your ability to change focus for various distances reduces, and so multi-focal lenses start to become valuable. When you first get them, they suck, but as your focus ability declines, they can become more useful. Bifocals (and, similarly progressives) are meant to give you easy access to reading at short (book) distances. Progressive lenses have two advantages over regular bi/tri focals:
- you can focus at ANY distance by choosing how low in the progressive field you place the prime focal point, and
- they look nicer (they make it less obvious that you are now old enough to need bifocals.
The problem with progressive is that (as pointed out), they have a smaller sharp-focus field, at any distance, and they take more getting used to. (once you get used to them, they are, actually, pretty useful for a lot of things)
One problem for computer users is that -- especially for desktop uses, we often are reading at mid distances -- neither far focus nor book distances. This is outside the historical "Best Practice" for the optometric profession. The first time my mom 'surprised' me with progressive lenses, we had a long talk about how my distances were not 'normal'.
What I would suggest doing is talking to your optometrist about the standard distances you encounter at work. (use a tape measure and actually MEASURE the distances), then come up with a bifocal pair for those> distances... having some hard numbers will also make it a bit easier for your optometrist to determine whether multi-focal lenses are even a good idea. This would probably also mean talking to a real optometrist, and not just an optician (essentially just an optical technician).
The probable best result (my guess) would be two pairs of glasses -- one set for work distances, and another set for 'normal' uses. If you go that path, you might want consider avoiding the 'pretty' stuff for the 'work' pair (i.e. don't bother with really high density glass, or anti-reflection coatings) It'll make the second pair that much cheaper.