[Argus25]

It should be understood that bifocal glasses BF or multi focal glasses MF's are a compromise and an attempt to fit a dual lens into a single glasses frame. As a result, compared to separate glasses for separate working distances, there are compromises, and they are different compromises for bifocals, trifocals and multifocal glasses.

Multifocals have no line in the glass above the reading or near segment. The curves in the glass (or plastic) are blended together. As a result there is on optical channel with fairly severe distortions on other side. So if you look downwards and left and right there is distortion and image swim. People like them though because there is no line in the glass and a gradual blend of the focus from far to near with BF's.

Bifocals are better because when you look below the line in the glass the focal power of the segment is the same anywhere, you can look left and right with minimal distortions, that is if it is a large size bifocal segment that is high set with a straight line across the lower 1/3 at least of the whole lens, these sorts of things suit engineers better. These were called "executive " bifocals. Yet some Optoms make glasses with very small semicircular bifocal windows which again, like the MF might improve the cosmetic look, but are less functional. On the other hand there is a sudden jump in the focus from far to near.

There is no beating separate distance and near glasses for quality and freedom from optical distortions. If there is any issue with potential falls etc I would avoid walking around in MF glasses and be careful with BF's too.