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.
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