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Bifocals Contacts

Bifocal lenses are that which have two (bi-) focusing powers (-focal). They allow a wearer to be able to focus on distant and close objects depending on what part of the lens they look through. From their invention in the mid-1700’s by Ben Franklin to modern day, most bifocal lenses are found in eyeglasses. Recently, bifocal contact lenses have been developed, giving people another vision correction option.

Bifocals are designed to help those with presbyopia. This condition is associated with aging and makes it difficult to focus on near objects. With bifocals, one can correct their nearsightedness caused by presbyopia along with farsightedness one may have. There are different types of bifocal lenses that are created in order to best fit an individual’s eyes.

There are two main types of lenses. The first is alternating vision, meaning the type of correction depends on where your pupil is directed. This type of lenses is similar to the traditional bifocal lenses found in eyeglasses: looking through the top half will correct for distance vision and the bottom is used for near vision. This works because the lens is shaped in such a way that it stays in place as you move your pupil or blink. The distance correction is larger than the near one, meaning looking straight ahead has a distance correction on it. 

The second type of lens is simultaneous vision. This type of lenses has different levels of corrective power in the same field of view. Within this category there are two types of lenses. Concentric lenses have circles of alternating power starting in the center and then radiating outward. Both near and far corrections are located within the area of your pupil. Your brain can “select” which power to use when attempting to focus on something either near or far. The lens may be center-near or center-far (referring to the type of correction) depending on the material. In some cases, the lens may have opposite center corrections.

Aspheric lenses are the other type of simultaneous vision lens. These start with one type of optical power and gradually progress to the opposite. The brain once again is able to select the power needed for the object you are attempting to focus on. Their design makes them the best multifocal option in most cases.

Multifocal lenses can be made out of a variety of materials to best match the comfort level of the individual. Lenses come in the standard soft and hard options. Hybrid contacts are also a good option. They are part hard, in order to keep the contact in place, and part soft, in order to increase comfort. Silicone lenses are available which have higher oxygen permeability to help combat dry eyes. Lenses normally come in weeklies, bi-weeklies, or monthlies. They sometimes come as dailies. Annual and bi-annual contacts are rare. See our articles on lenses to learn about the tradeoffs of each. 

Bifocal lenses are used in a technique called monovision. One eye will have a single corrective power, while the other will have a multifocal lens. With both eyes open, an individual is able to see at all distances at once.