What is the difference between bifocals and varifocals?
Bifocals have two distinct sections:
The top part is for distance vision, such as seeing across a room or driving.
The bottom part is for close-up vision, like reading a book.
There is a visible line separating these two sections. When switching between looking at something far away and something close, you have to move your head to look through the correct part of the lens. The downside is that there is a "jump" in your vision at the line, and they do not provide correction for middle distances, such as a computer screen.
Varifocals, also known as progressives, function more like a smooth gradient:
The top is for distance.
The middle gradually transitions for intermediate distances.
The bottom is for close-up work.
There is no visible line, and your vision transitions smoothly as you look up and down through different parts of the lens. This allows you to see clearly at all distances, not just two fixed points.
The main advantage of varifocals is that they are more natural and versatile, eliminating the jarring jump in vision.
The main advantage of bifocals is that they are simpler to adapt to and usually less expensive.