November 13, 2013

Bifocal Contact Lenses

If you wear contact lenses, sometime after age 40, you will begin to notice that your contacts don’t work as well for reading and other close-up tasks as they once did.

This is a sign that you are developing presbyopia — a normal aging change that reduces your eyes’ ability to focus on near objects.

Presbyopia happens to everyone; it doesn’t matter if you wear contacts, eyeglasses or you have perfect vision without corrective lenses. Eventually it catches up to you.

More and more people — especially those who already wear contacts for nearsightedness, farsightedness or astigmatism — are finding that the best solution for the frustration of presbyopia is bifocal contact lenses.

What Are Bifocal Contact Lenses?

Bifocal contact lenses are premium contacts that have two or more power zones to correct both distance vision and near vision for people with presbyopia.

Some “bifocal” contact lenses have more than two powers, and are more similar in design to progressive eyeglass lenses that have a gradual transition in lens power to provide clear vision at all distances. For this reason, many eye care professionals prefer the term “multifocal contact lenses” rather than bifocal contact lenses for these presbyopia-correcting contacts.

In fact, many eye doctors and opticians use the term “multifocal contact lenses” to describe any type of contacts with more than one power that are designed to correct presbyopia — whether they are bifocals (two powers), trifocal (three powers; for distance, intermediate and near vision) or progressive-style multifocal contacts.

Bifocal and other multifocal contact lenses are available in several lens materials, including hydrogels (conventional soft lens materials); silicone hydrogels (advanced soft materials that allow more oxygen to reach the eye); and rigid gas permeable (RGP or GP) plastics.

There also are “hybrid” bifocal contact lenses, which have a rigid gas permeable optical zone in the center of the lens for excellent optics, surrounded by a silicone hydrogel material for easier adaptation and (sometimes) greater wearing comfort than GP bifocal lenses.

Bifocal and Multifocal Contact Lens Designs

Unlike bifocal, trifocal and progressive eyeglass lenses, which are stationary in front of the eyes and held securely in place with eyeglass frames, bifocal and multifocal contact lenses (like all contacts) rest on a layer of tears on the surface of the eye and must move with each blink to keep the eye comfortable and healthy.

Therefore, a sophisticated lens design is required to keep the different viewing zones of bifocal and multifocal contacts in proper position for good vision.

There are two general types of bifocal and multifocal contact lens designs:

Simultaneous vision lenses. In these lenses, the distance and near zones of the lens are in front of your pupil at the same time. Though it may take some time for your eyes to adapt to simultaneous vision lenses, eventually your visual system learns to use the power you need and ignore the other lens power(s), depending on whether the object you are focusing on is far away or up close.

Most soft bifocal lenses have a simultaneous vision design. There are two variations:

Concentric ring multifocals — These are bifocal lenses with either the distance or near power in the center of the lens, with alternating rings of distance and near powers surrounding it.
Aspheric multifocals — These are progressive-style multifocal contacts, with a gradual transition in lens power from the center of the lens outward. Some aspheric lenses have the distance power in the center of the lens; others have the near power in the center.
Alternating vision (translating) lenses. These are rigid gas permeable multifocal contacts that are designed like bifocal eyeglass lenses. The top part of the lens has the distance power, and the bottom part of the lens contains the near power.

When you look straight ahead while wearing translating bifocal contacts, your eye is looking through the distance part of the lens. When you look down, your lower lid holds the lens in place while your pupil moves (translates) into the near zone of the lens for reading.

Alternating vision multifocal contacts usually include special weighting or a modification of the contour of the bottom edge of the lenses to maintain the proper positioning of the distance and near zones and avoid unwanted lens rotation.

Which Bifocals Contacts Work Best?

Most people who try bifocal or multifocal contact lenses and have realistic expectations are very pleased with their vision and the convenience of having little or no need for reading glasses throughout the day.

But, As with wearing bifocal or progressive eyeglass lenses, there are some visual compromises when wearing multifocal contact lenses.

Some wearers will notice their distance vision with multifocal contacts is not as crisp, compared with wearing regular (single vision) contact lenses. And reading glasses still may be necessary for reading small print or reading in dim lighting (viewing a dinner menu in a restaurant, for example.)

The only way to accurately determine which type of bifocal or multifocal contact lenses will work best for you is to have a comprehensive eye exam, consultation and contact lens fitting.

Because fitting multifocal contacts requires more time and expertise than fitting regular contact lenses, fitting fees are higher for multifocal lenses. Also, due to their greater design complexity, multifocal contacts cost significantly more than regular contact lenses.

For specific information about costs associated with bifocal and multifocal contacts, and to see if you are a good candidate for the lenses, schedule a visit with an eye care professional who routinely fits these premium contact lenses.

Bifocal Contact Lenses