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| Bifocal Contacts, Multifocal Contacts – What's the Difference? |
| Bifocal contacts lenses have two prescriptions in the same lens. Multifocal contact lenses have a range of powers (similar to progressive spectacle lenses) in each lens. "Multifocal" is also used as a catch-all term for all contact lenses with more than one power, including bifocals. |
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| How Multifocal Contact Lenses Work |
| Bifocal and multifocal contact lenses work in several different ways, depending on the design of the lens. The designs fall into two basic groups: |
- "Alternating vision" (translating) lenses are so named because your pupil alternates between the two powers, as your gaze shifts upward or downward.
- Simultaneous vision lenses require your eye to be looking through both distance and near powers at the same time. Although this might sound unworkable, your visual system learns to select the correct power
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| choice depending on how close or far you're trying to see. Simultaneous vision lenses come in two types: |
- Concentric ring designs
- Aspheric designs
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| Alternating Bifocal Contact Lenses |
| Alternating or translating bifocals work much like bifocal eyeglasses. They have two power segments, with an obvious line of separation between the distance correction on top and the near correction below. Your pupil looks through either one or the other, depending on whether you're looking far or near. With bifocal eyeglasses, this mechanism works because the lenses stay in place even as your eye moves. That can happen with contact lenses, too. Since most alternating bifocals are GP lenses, they are smaller in diameter than soft lenses, and they ride on your eye above your lower eyelid. Therefore, when your gaze shifts downward, the lens stays in place, allowing you to see through the lower, near-correction part of the lens. |
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| Concentric Ring Designs |
| This type of bifocal contact lens features a prescription in the center and one or more rings of power surrounding it. If there are multiple rings, they alternate between the near and distance prescription. Typically at least two rings are within your pupil area, but this varies as your pupil expands and contracts due to varying light. |
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| Concentric ring bifocal contact lenses can be made of either soft or rigid (GP) material. The locations of the powers will vary: |
- GP bifocals usually have the distance power in the center (called center-distance).
- Soft bifocal contact lenses usually have the near power in the center (center-near).
- Some soft multifocal designs are center-near on your dominant eye but center-distance on your non-dominant eye.
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| Aspheric Multifocal Contact Lenses |
| These multifocal contact lens designs work more like progressive eyeglass lenses, where the different prescriptive powers are blended across the lens. Unlike eyeglasses, however, aspheric contact lenses are simultaneous vision lenses, so your visual system must learn to select the proper prescription for the moment. This is the only type of multifocal contact lens that can be described as "progressive." It's also concentric, like the concentric ring designs, and it has become the most popular type of multifocal contact lens. |
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