Difference between single vision, bifocal and progressive
1. Bifocals help you get far and near vision only, and will generate image jumps when you look near after you see distance.
2. You will get continuous vision at distant, middle, and near focal ranges with progressive lens, and with no lines, no annoying image jumps.
3. progressive lens will be more expensive than bifocals. But the extra price is worthy of its value.