If you already are wearing corrective eyeglasses, multifocal lenses will most likely be your best option. So let’s start with bifocals.
People who like bifocals prefer having their distance and near vision clearly separated by a visible line. They don’t care, or are less concerned about, what this implies about their age. However, people who don’t like the way bifocals correct their vision complain about the phenomenon known as “image jump”, which refers to the abrupt switch from distance to near vision, which can be disorienting.
Presbyopes who want a smoother blend between distance and near vision tend to prefer multifocal lenses with no visible line separating the larger distance portion and the smaller near segment. These invisible line bifocals (or, more accurately, multifocals) are called progressives.
That’s because the vision “progresses” from distance to near vision with no image jump. In addition, in between the portion of the lens with distance vision and the portion with near vision, there is a portion of the lens that provides intermediate or computer vision.
Let’s look at these no-line multifocal lenses a little more closely. Progressives could also be called no-line trifocals, because there are three fields of vision in the lens with no visible line separating them. This is great for disguising your need to wear “old people’s glasses” but it comes at a cost. Literally, since progressive eyeglasses are, as a rule, more expensive than single-vision or bifocal glasses. But there’s also an aspect to pay attention to in terms of the amount of vision correction on the lens.
The reading-segment lens of bifocals is, as we noted, roughly 28 millimeters across. But with progressives, the reading segment lens is about half that, roughly 14 millimeters across. In addition, there is no vision correction on either side of the reading portion of the lens.
To get a sense of how a progressive lens is configured, think of a mushroom.
Imagine the cap is the distance-vision section of the lens. Think of the mushroom’s stem as the intermediate and reading portion of the lens, around 14 millimeters wide. People who prefer the wider reading segment provided by bifocal lenses often feel that the progressive lens doesn’t provide a wide-enough near-vision reading corridor.
Progressives won’t work for everyone, though. Some people respond adversely to the lack of a visible line separating the three focal fields, to the point of feeling dizzy or nauseous while wearing progressives. For most first-time progressive eyeglasses wearers, this goes away in a few minutes or a few days.
For some people, however, the discomfort they feel wearing progressives never goes away. Moreover, wearing a pair of multifocal glasses, bifocals or progressives, can be dangerous for some people, according to research published by Investigative Ophthalmology & Visual Science. This study found that people wearing either bifocal or progressive glasses are more than twice as likely to fall when wearing multifocal glasses than they are while wearing single-vision glasses. This increases if the wearer is walking downstairs.
People who feel they might have a hard time maintaining their balance while wearing multifocal glasses, or who have tried and dislike bifocals and progressives, would very likely do better with separate pairs of single-vision glasses for distance, computer and reading vision.