So I wear multifocal glasses with 4 lenses in them and I understand how they work. But I can’t understand contacts. How do you look through the different lenses if the contacts move with your eyes?
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So the way a lens works is by ‘bending’ light, so that objects through the lens appear larger or smaller. When the lens is close to your eye, this doesn’t really happen much, but the effect is that it moves the focus point of the lens forwards or backwards.
With bi/multifocal lenses, this happens on multiple areas of the lens, so that at close distances it may bend light in a certain way which helps focus close objects, and the same for far objects too, because the lens of the eye treats them differently. Usually with contact lenses, the multifocal area surrounds the centre of the lens in a ring, but can also be certain regions of the lens depending on the design. With a simple multifocal, the centre will start out with one power (level of focus), and progress to a different power as you move out towards the edge of what’s called the ‘optic zone’ – usually it becomes more negative, or widening, relative to the centre power IIRC.
Source: used to make contact lenses for a living.
Bifocal or multifocal contact lenses are designed to correct presbyopia, a condition that affects your ability to focus on near objects as you age. They have different zones or rings of power that allow you to see clearly at different distances.
There are two main types of bifocal or multifocal contact lenses: **segmented** and **concentric**.
Segmented bifocal lenses have a defined line between the top and bottom sections of the lens, like bifocal glasses. The top section is for distance vision and the bottom section is for near vision. These lenses are usually rigid gas-permeable (GP) lenses that do not move with your eyes. Instead, they stay in place when you blink or look up and down.
Concentric bifocal or multifocal lenses have either the near or distance power in the center of the lens and the opposite power in the outer area of the lens, like a bullseye target. These lenses can be soft or hard, and they move with your eyes when you blink or look around. Your eyes will automatically adjust to the different powers depending on what you are looking at.
The answers regarding multifocal CL’s are good. I’d just add that your glasses do not have “4 lenses in them”. If they’re lined bifocals, there are 2 different zones of power. If they’re lined trifocals, there are 3 zones of power. Trifocals aren’t very common these days. If they’re unlined/”no-line” bifocals aka progressives, there are technically infinite powers bc the power changes gradually between the distance and near portions of the lens. Regardless, it’s still just one lens per eye.
For bifocals, one solution is to have a different lens on each eye. It doesn’t work for everyone, but if your brain can accommodate the difference, you can have one eye for distance and the other for reading
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