Bifocal and Multifocal Contact Lenses

Bifocal Contact Lenses  - How do they work?

If you are over 40 years old and have problems seeing close up, you probably have a common age-related condition called presbyopia.  The eye loses its natural ability to focus on close objects.  Eventually the arms don't seem long enough because reading material is held farther away from the eyes in order to see clearly.

Fortunately for those who do not like the look or inconvenience of reading glasses, there is another option.  Bifocal contact lenses are available in both soft and rigid gas permeable (RGP) varieties.

Multifocal contact lenses are generally designed in one of two ways, as either simultaneous vision lenses or alternating vision lenses.

The most popular version of multifocal contact lenses, simultaneous vision lenses present the distance and near vision zones of the lens at the same time.  Typically after a short adjustment period your eyes learn to focus on objects and filter out the other zones.  Concentric ring design is a bulls-eye pattern with each circular area having a lens power that gradually changes allowing near and far vision.

The alternating or translating vision lenses have distinct areas for near and far vision.  The pupil will move to the desired zone depending on your vision needs.  Typically the top of the lens is for distance vision and the bottom area (what you look through when you look down) is for near vision.  Translating lenses are held in place by a ballast which is a thicker area than the rest of the lens, or by flattening the bottom of the lens to stay aligned with the lower lid.  These translating lenses are available in rigid gas permeable (RGP) lenses.

Newer scleral lenses are large RGP with good comfort available in multifocal lens  powers, also using simultaneous vision design.

If you have presbyopia, contact lenses may be a great option for you over traditional reading glasses.  Contact lens manufacturers have done much research for the baby boomer market to offer more multifocal contact lens choices.   Speak to Dr. Dianna Leong, Dr. Anh Bui and Dr. Thomas Jay Yung about the new contact lens options available.

The Difference Between Bifocal and Multifocal Lenses

Just as the name indicates, bifocal lenses are divided into two distinct segments for different vision powers, the first for distance vision and the second for near vision.  This enables you to clearly switch your focus from near to far as needed, but your vision will not necessarily be clear in between. The term multifocal lenses can refer to any lenses with multiple powers including bifocals, trifocals or progressive lenses. Non-bifocal multifocal lenses have a range of powers that enable you to constantly adjust your focus to see clearly from up close to far and in between.

Multifocal contact lenses are generally designed in one of two ways, as either simultaneous vision lenses or alternating vision lenses.

Simultaneous vision lenses

The most popular version of multifocal contact lenses, simultaneous vision lenses present the distance and near vision zones of the lens at the same time.  Typically after a short adjustment period your eyes learn to utilize the segment of the lens that they need to focus on the desired object and essentially ignore the other.

They come in two designs:

• Concentric ring design: In the most basic form these are bifocal lenses that are comprised of a central circular area of one power with a ring around of the alternate power, similar to a bulls-eye.  In this design the power of the rings (either near or distance vision is interchangeable).  For intermediate viewing (18-24 inches away) extra rings can be added to create a trifocal or multifocal lens.  The width of each ring is variable depending on the power that is needed most and the edges of the rings can be blended for a smooth transition of focus, similar to progressive eyeglass lenses.

• Aspheric design: These multifocal lenses attempt to provide a natural vision experience by blending many lens powers across the surface and center of the lens. In this design both distance and near vision power are located in the central visual area and your eyes will adapt to focus on the area needed to view what you are looking at.

Translating or Alternating Vision lenses

Similar to bifocal eyeglass lenses, these contacts are divided into distinct areas or zones and your pupil will move to the desired zone depending on your vision needs. Typically the top of the lens, which is what you look through when looking straight ahead is for distance vision and the bottom area (what you look through when you look down) is for near vision. However, this can be reversed according to unique vision needs.

Since contact lenses sometimes move within your eye, translating lenses are held in place by a ballast which is an area that is thicker than the rest of the lens or by truncating or flattening the bottom to stay in line by the lower lid. These lenses are only available in rigid gas permeable lens material.

An Alternative Option to Multifocal Contact Lenses: Monovision

Monovision is another contact lens alternative for presbyopia particularly if you are having difficulty adapting to multifocal lenses.  Monovision splits your distance and near vision between your eyes, using your dominant eye for distance vision and your non-dominant  eye for near vision.

Typically you will use single vision lenses in each eye however sometimes the dominant eye will use a single vision lens while a multifocal lens will be used in the other eye for intermediate and near vision. This is called modified monovision.  Your eye doctor will perform a test to determine which type of lens is best suited for each eye and optimal vision.

Are Contact Lenses Right for You?

If you have presbyopia, contact lenses may be a great option for you. Many people prefer the look and convenience of contact lenses over traditional reading glasses. Speak to your Calgary eye doctor about the options available to you.