As we get older, our eyes lose the ability to change focus from distant objects to near ones. This loss of accommodation is called presbyopia, and it happens to just about everyone, usually starting around age 40. For most people, the biggest problem with presbyopia is reading. As the ability to focus on close objects gradually diminishes, reading becomes more difficult, particularly when the print is small, the contrast is poor, or the reader is tired.
Good News, Bad News
Presbyopia is an entirely natural and normal phenomenon. While presbyopia won’t go away–our eyes won’t learn to accommodate again–there are many simple and effective ways to deal with it. In the past, reading glasses or bifocal spectacles took care of the problem for just about everybody. Bifocal contact lenses have been available since 1947. There are a number of manufacturers of bifocal contact lenses and many contact lens fitters who specialize in bifocals. That’s the good news. The bad news is that contact lens correction of presbyopia is not for everybody. While many wearers are quite pleased with their bifocal contact lenses, others find themselves either unable to adjust to the lenses or dissatisfied with the vision they provide. In addition, bifocal contact lenses usually cost more than standard “single-vision lenses.” Your vision (without lenses) and your specific near visual needs are important in determining whether bifocal contact lenses make sense for you. With bifocal contact lenses, visual requirements and patient motivation often make the difference between success and failure.
Correcting Presbyopia-Segmented Lenses
Presbyopes (people with presbyopia) often need correction for both distance and near vision. Hence, bifocal glasses have a distance portion and a reading (near) portion. You look through the upper (distance) portion of the lens to see far objects and through the lower (near) portion of the lens when reading. Some bifocal contact lenses are designed in a similar way. Like bifocal spectacle lenses, contact lenses can be made with the distance portion on top and a near portion at the base. Bifocal contact lenses designed this way are called segmented lenses. While the basic design of segmented contact lenses reminds one of bifocal glasses, segmented contact lenses don’t work in exactly the same way. With a bifocal spectacle lens in front of your eye you can direct your gaze through the portion of the lens you need.
With segmented bifocal contact lenses the top portion is for distance vision and the bottom segment is where the near, or reading vision, is located. When looking straight ahead, you will be in the distance portion of the lens, and when you look down to read, the lens will move slightly to bring the near vision segment into the line of sight. A number of design features help to position the segmented lens on the eye. For example, the lens may have a flat bottom edge to allow the lower eyelid to assist in positioning; or it may be weighted on the bottom to prevent rotation. Because lens position is critical, the fitting of segmented lenses requires skill and patience. Several visits to your practitioner may be required in order to get a fit that’s just right. A problem that can occur with poorly made segmented lenses is “image jump”: a sudden displacement of the object being viewed that can take place as the line between the segments moves through the path of vision. Segmented contact lenses provide alternating vision. That is, when you look through the near vision segment, close objects are in focus; while distant objects are in focus when you look through the distance segment.
A different kind of bifocal contact lens allows both distant and near objects to be in focus at the same time. Called simultaneous vision, this design puts the near correction and the distance correction in concentric rings. Since both the distance and near portions of the lens are within the line of sight at all times, light from both distant and near objects can be in focus in the eye at the same time. But this has limitations. While the eye is seeing through the contact lens, some light from distant objects is passing through the near vision part of the lens and some light from near objects is passing through the distance portion. So the eye receives both in-focus and out-of-focus images at the same time. In simultaneous vision, it is up to the brain to select the desired image. While simultaneous vision lenses avoid image jump and allow for a simpler lens design–the lens position is not as critical as it is for segmented designs–not all wearers are able to adjust to simultaneous vision.
In addition to the standard simultaneous vision bifocal contact lenses that put the distance and near corrections in concentric rings, there are several related lens types. Aspheric contact lenses change lens power gradually, from the center to the edge of the lens. Because the change in lens power is gradual, correction for intermediate distances is possible. This design usually requires two weeks of continuous wearing to adapt to the lens. The diffractive contact lens uses a series of concentric grooves, cut in the back surface of the lens, to provide the near vision correction. In general, image resolution is better with diffractive lenses than with other simultaneous vision lenses, and there is less initial blur. Occasionally, in certain lighting situations, some wearers report seeing a ” ghost” image or halo effect.
An alternative to bifocal lenses is to correct one eye for distance vision and the other eye for near vision. This technique is called monovision. Since there is only one correction in each lens, this avoids the problems associated with either simultaneous or alternating vision. Fitting is simpler, and the lenses can be less expensive. However, monovision also requires a period of adaptation. And while some people adapt well to monovision, others don’ t like the loss of binocular vision it causes. (Binocular vision is the ability to use both eyes to see objects in three dimensions.) Because depth perception is altered with monovision, additional correction may be needed for driving and operating heavy equipment. Under these circumstances, driving glasses to correct the reading eye for distance and improve binocular vision are recommended. Similarly, some wearers may require an additional near vision correction in the distance eye to allow prolonged or concentrated reading. A variant of monovision, modified monovision, puts a bifocal contact lens in one eye and a single-vision contact lens in the other eye. This can give binocular vision for driving, while still permitting near vision for reading.
Reading Glasses-One More Option
Another alternative for the presbyope who would like to avoid glasses as much as possible involves wearing single-vision contact lenses for distance and reading glasses for near vision (without removing the contact lenses). While this does not solve the problem for people who want to be entirely free of glasses, it is a simple alternative that can save time and money. In addition, there is no difficult period of adaptation.
As we have seen, there are several ways to fit presbyopes who would like to wear contact lenses. If you can wear contact lenses, one of the alternatives presented should meet your needs. Because there are so many options, it is important to discuss the matter fully with your eye care professional. In helping you reach a decision, your eye care professional will consider your vision, the health of your eyes, and your specific visual needs.
Getting Used to Bifocal Lenses
Adapting to bifocal contact lenses or to monovision takes time-in addition to the normal time it takes to adapt to any contact lens. If you would like to wear bifocal contacts, you should be prepared for a period (likely to be several weeks) of adaptation. In addition, you should be prepared for the possibility of extra visits to your eye care professional to ensure that the lenses fit properly and meet your needs. Presbyopes should also be prepared for the possibility of failure. It may turn out, for example, that simultaneous-vision lenses are just not for you. In that case, your eye care professional may suggest some other option, such as monovision or segmented lenses. A strong desire to wear contact lenses is a big help here. It can take a while (and sometimes one or two changes) to find a solution that meets your needs. If you’re unsure whether you really want to wear contact lenses, the time and expense required to get a satisfactory fit with bifocal lenses may prove too much.
It Gets Better
While it may take some time for presbyopes to get used to bifocal contact lenses or to monovision, once fit with a pair of contact lenses that work, they are just like any other contact lenses. After the initial fitting period, you won’t have to return to your eye care professional more often than other contact lens wearers. And, because your lenses are made of the same high quality materials as other contact lenses, they require the same care. Though the initial fitting is more involved, once you’re happy with your lenses, you’re likely to stay that way.
The above information is taken from the CLAO Patient Information Pamphlet titled BIFOCAL CONTACT LENSES. Pamphlet Advisor was Ronald H. Akashi, MD. Copyright 1996-2004 Contact Lens Association of Ophthalmologists, Inc. Thanks to Contact Lens Docs for content used in the creation of this website. All rights reserved. Reproduction other than for one-time personal use is strictly prohibited.