Bifocal and Multifocal Contact Lenses

By John L. Burns, OD

Eye Design Family Eyecare Center

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Bifocal and Multifocal Contact Lenses

Bifocal contact lenses are designed to provide good vision to people who have a condition calledpresbyopia. The main sign that you're developing presbyopia is that you need to hold menus, newspapers and other reading material farther from your eyes in order to see it clearly.

Bifocal contact lenses come in both soft materials andrigid gas permeable (GP) materials. Some can be worn on adisposablebasis. That means you have the convenience of throwing the lenses out at specified intervals and replacing them with fresh, new lenses.

Bifocal and multifocal contact lenses work in several different ways, depending on the design of the lens. The designs fall into two basic groups

1. “Alternating vision” (translating) lenses are so named because your pupil alternates between the two powers, as your gaze shifts upward or downward.

2. “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 choice depending on how close or far you're trying to see. Simultaneous vision lenses come in two types concentric ring designs and aspheric designs.

Alternating Bifocal Contact Lenses

Alternating bifocals work much like bifocal glasses. They have two power segments, with an obvious line of separation between the distance correction on top and the near correction below. Your eye 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 thansoft 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.

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. Some soft multifocal designs are center-near on your dominant eye but center-distance on your non-dominant eye.

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.