Bifocal Contact Lenses
Rigid Gas Permeable Multi-Focal Lenses
Rigid Gas Permeable Lenses (RGP's) have enjoyed increased popularity over the past 20 years. New developments in designs and materials have made these lenses more comfortable and healthier to wear than ever before. The advantages of RGP's over soft lenses include; higher levels of oxygen transmission to the cornea, greater durability and deposit resistance and therefore greater life expectancy, and unmatched optical performance. RGP's are the primary lens design of choice for bifocal/multifocal lenses due to their sharp optics. Patients who have irregular corneal surfaces will experience distorted vision with glasses and with soft contact lenses. A variety of RGP designs are fit at Vision Professionals to provide clear and undistorted vision for patients suffering from corneal disease, corneal trauma, or irregular corneas following certain eye surgeries. Our doctors will recommend RGP's for you if they are in your best interest.
Our doctors have two choices when deciding what type of RGP bifocal will be right for you. The first type of bifocal is a no line multi-focal and the second is a segmented (or lined) bifocal.
NO LINE MULTI-FOCAL
The most common no line multi-focal that we fit in our practice is the Essential bifocal.
This lens has a "bulls-eye" in the center of the lens which will correct the distance vision. From the "bulls-eye" to the peripheral part of the lens the back surface gradually flattens to build in the bifocal component. The degree of flattening increases as the series of bifocal increases (series 1 to 3).
Advantages: The Essential bifocal is a no-line multi-focal which means it gives the patient distance, intermediate and near vision. One advantage of this lens is it has 3 series of bifocals which increase in bifocal powers (most no-line bifocals only come in one bifocal power). The lens is not weighted since the bifocal goes completely around the perimeter of the lens so rotation of the lens is not important. By not having to weight the lens it is the same thickness as a distance only rigid gas permeable lens. Distance and intermediate vision is normally very good while the near vision is ideal for newspaper and magazine type print.
Disadvantages: This lens may not be adequate for very small print (as you may see on the back of a medicine bottle). Some patients may feel that a low power pair of reading glasses are needed to see the very small print. Also, since the bifocal of a no line multi-focal is always on the back surface of the lens there may be some blur when wearing glasses after removing the lenses after a days wear, this is known as “spectacle blur”: The flattening of the lens curvature can also temporarily flatten the cornea (front surface of the eye) resulting in making the eye less nearsighted. In effect, the glasses will be temporarily too strong. Within a few hours the corneas will go back to their original curvature and glasses will again be clear. This will only be an issue if the patient wants to insert the lenses in the morning and wants to remove them when getting home from work (5 or 6 o’clock). There may be a couple hours where vision thru glasses will be slightly fuzzy.
The most common segmented bifocal we fit in our practice is the Tangent Streak by Fused Contacts. This lens contains the bifocal on the front surface where there is a visible (although very difficult to see) line going across the lens separating the distance (top) and the near (bottom). Because this lens has a "top" and "bottom" the lens must be weighted (or prism ballast). This results in a slightly thicker lens on the bottom half. In order for the lens to fit properly, the lens must rest on the lower lid, not rotate and show minimal vertical movement. The weighting of the lens will control all of those fitting aspects.
Advantages: This lens gives very good distance vision (very similar to the no line multi-focal). Near vision is extremely good. With this lens small print (as on the medicine bottle) is excellent. With this lens distance and near vision can be ordered to exacting specifications. Whereas the no-line multi-focal is limited in maximum bifocal strength, the segmented bifocal has no limitations. Therefore, the patient will never "outgrow" this lens from a strength standpoint. There is no spectacle blur with this lens since the bifocal is on the front surface (as opposed to the back in the no-line). A patient can go back and forth between glasses and their bifocals and experience no spectacle blur.
Disadvantages: The lens is slightly thicker due to the weighting of the lens therefore wearing time in some cases is slightly less. The lens does not have intermediate vision. It only has distance and near.
The segmented lens does come in a trifocal design although it is generally used with patients who have already adapted to the segmented bifocal (one line). After adapting to one line, getting used to the second line does not seem to be a problem. However, starting out with a trifocal (2 lines) can sometimes be a difficult adaptation.
For more information on contact lenses, visit www.contactlenses.org
Please feel free to call our office to schedule an appointment to find out if bifocal contact lenses are right for you. Worthington: 614-846-7574 or New Albany: 614-855-7574