RGP bifocal contact lenses are the answer if you aren’t satisfied with soft bifocal contacts. Bifocal gas permeable lenses promise you a greater vision. GP lenses are made from stiff plastic material that keeps their shape better than soft contacts when you blink. If you wear these lenses you won’t suffer strained-eyes because of the needs to continually refocus.
If you have presbyopia chances are you’re more susceptible to dry eye syndrome. Since soft contacts contain water they tend to absorbs protein and other deposits from your tears. These create scratchy, uncomfortable feeling. Fortunately, rigid gas permeable lenses don’t contain water.
If you also have astigmatism soft contacts don’t produce your desired visual acuity, GP lenses are the answer. For a small amount of astigmatism RGP bifocal contacts can compensate a need for an astigmatic correction. Your cornea, after an adaptation period, will conform to the shape of the lens.
Types of RGP Bifocal Contact Lenses
Based on how each lens correct vision, there are three RGP bifocal contact lens types: concentric or annular, aspheric or simultaneous, and translating or alternating. The following are a brief description of each lens design.
- Concentric or Annular Lens. This lens design utilizes concentric or annular rings in a bulls-eye pattern. Here the near vision correction is in a small circle at the center of the lens, while the distance vision correction is at the outer circle. Or, the distance correction is in the center, surrounded by the outer circle as the near correction. There is a concentric design that offers intermediate vision correction. This design adds an additional ring between near and distance correction rings. There is also a type with blended intermediate and distance rings that works like progressive eyeglasses.
- Aspheric or Simultaneous Lens In aspheric design, both near and distance vision prescriptions are near the pupil, in the central visual area. The lens produces a varying power continuously from the center radially toward the edge. With the gradual change in power you can have intermediate distance correction. Similar to concentric design, some designs position the distance optics in the center of the lens, and others place the near correction in the center. And like spectacle lenses, this design is also known as “progressive” or “no line” bifocal.
- Translating or Alternating Lens In this design the near prescription is on the bottom. So, when you read a book, your eyes move downward to see through the lower portion of the lens. And you’ll see distance by looking over the upper part.One translating design mimic “half-moon” segment of bifocal eyeglasses. The lower segment corrects near distance and the upper segment corrects distance vision. But the corrections can be reversed, if your work or hobby needs a near vision correction at the top.
Note: Unlike concentric and aspheric lenses, translating lens has to be stable from lens rotation since lens rotation may position near correction area to the wrong place. To maintain the near correction at the bottom, the multifocal lens is weighted or ballasted with extra thickness. In another translating design, the bottom part of the lens is flattened or truncated. With the truncation, your lower lid will “maintain” the lens in upward position.
An example of bifocal or multifocal contact lenses is boston multivision from Bausch + Lomb.
Are You a Good RGP Bifocal Candidate?
Who is a good candidate for concentric, aspheric or translating gas permeable? The following information may help you understand the right lens for your vision needs:
- Concentric design. Concentric lenses suit your vision needs if you’re at early stage of presbyopia, have small to medium pupil diameters and need a good near vision above eye level. But they have limitations. Since both near and distance objects passing through distance and near portions of concentric lenses you’ll experience out-of-focus until your brain select the desired image.
- Aspheric design. Aspheric lenses work well if you’re at early stage of presbyopia and you need intermediate distance correction. They usually also deliver better image resolution than concentric lenses.
- Translating design. Translating lens also offers enough near correction for presbyopes at later stages. If you have large pupil diameters translating lenses can accommodate them. But if you’re active in any contact sports spherical RGPs or daily disposable are better alternatives than alternating lenses.
Still confused and undecided? Visit your eye doctor to see if RGP bifocal contact lenses are right for you. A good eye doctor will help you to fit the contact lenses that is best suited to your vision requirements.