Eye Facts

Presbyopia, Why Bifocals?

It happens to almost everyone at middle age. You begin to hold the newspaper farther away to read. Fine objects close to you look blurred. This is Presbyopia.

What is Presbyopia?

Presbyopia means “age of sight.” It is not the same thing as farsightedness. It is a gradual loss of accommodation – the ability of the eye to adjust in order to see clearly objects at different distances. To accommodate this ability, the naturally elastic lens of the eye changes in shape and thereby adjusts its focusing power. Loss of accommodation occurs gradually throughout life. As the lens of the eye ages, it becomes less elastic, which results in less accommodative power.

Each year four million Americans develop presbyopia. Presbyopia becomes a problem for different people at different times. Although presbyopia gradually worsens, it does not cause blindness and can easily be corrected with glasses.

When does Presbyopia start?

Presbyopia may begin as early as age 36 or as late as 50. Persons with no refractive error (no need for corrective lenses) will usually notice presbyopia in their mid-40s. Farsighted persons will note presbyopia earlier, especially when they are not wearing their glasses. Also, some conditions such as diabetes can result in an earlier onset of presbyopia.

How do I know if I have Presbyopia?

Symptoms – The most common indication is an inability to read fine print such as in the newspaper or phone book. This is worse with fatigue. To see small print, people with presbyopia must hold reading material farther from their eyes. Nearsighted people may need to take off their distance glasses to read. Other close work, such as threading a needle, may be difficult. Another symptom of early presbyopia is when distance vision stays blurred a few moments after an individual looks up from reading. Diagnosis – The simplest and most widely used test for presbyopia is the reading card. The patient reads a card with various sized letters and numbers, held 14 or 16 inches away. The eye doctor tests different lenses in front of the patient’s eyes to determine what correction is needed.

How is Presbyopia corrected?

Presbyopia may not need correction for a year or two after symptoms begin. Some people can simply change their reading distance, increase illumination, take frequent breaks from close work or, if nearsighted, remove their glasses to read.

Correction of presbyopia involves making up for the lost accommodative power of the lens of the eye. This is accomplished by use of a “plus” lens, which is similar to a magnifying lens. Because the lens of the eye continues to change with age, a stronger reading glass prescription is needed about every two years until the mid-50s or 60s. Little change is needed after that unless some other visual problem develops.

There are several options for correcting presbyopia:

Reading glasses – In reading glasses, the whole lens of the eyeglass contains the correction for reading. This provides good vision for close objects but makes distant objects look blurred. Therefore, reading glasses must be removed to see in the distance. These glasses are best for people who do not mind switching between distance and reading glasses, who do not need distance correction or who wear contact lenses for distance. They are also appropriate for people who can not wear bifocals for some reason. Half-glasses leave the top of the glasses open to facilitate distance vision without the need to remove the glasses.

Reading glasses are available with or without a prescription. Over-the-counter (dime store) “readers” generally cost much less than custom-made glasses. For some people, these nonprescription readers are effective. However, depending on your eyes, you may need prescription reading glasses. Therefore, your eye doctor can tell you if you can wear over-the-counter readers.

Bifocals are two lenses in one. One part, or segment (usually the bottom), is made to adjust the eye for close focus, and the other (top) has a different strength for distant focus. The key to wearing bifocals is to learn to automatically look through the proper part of the glass. Bifocals are somewhat difficult to get used to at first for several reasons:

Because the plus segment magnifies objects, things appear closer to the wearer than they really are. Walking down stairs may be difficult until the person learns to hold a different head position.

As the bifocal wearer’s eyes cross the junction of the distance and near segments, the image jumps up for a split second. Some styles of bifocal can lessen this image jump.

Images through the lower segment look like they are in a slightly different place than they really are.

Although almost every bifocal wearer has some initial problems getting used to the glasses, most people adjust to wearing them.

Bifocals have come a long way since Benjamin Franklin invented them in the 1700s. For people concerned about their appearance, “invisible” bifocals or bifocal contact lenses may be an option.

Invisible bifocals – Bifocals are available without a visible line dividing the segments. “Blended” or “seamless” bifocals have the segment line polished so that it is not visible as a distinct line. In the area of blending, some blurry vision results, which can make this type of bifocal more difficult to get used to than standard types.

Another type of lens with no visible line is called a progressive addition lens or variable-power lens. This lens acts somewhat like a trifocal (see below), in that it provides clear vision for far distance, intermediate distance (3-5 feet) and near. However, unlike bifocals or trifocals, it has a gradual change in power over the area of the lens. With this lens, vision down and to the side is somewhat blurred. Progressive addition lenses often take longer to adjust to and may cost more than bifocals.

Bifocal contact lenses-Current bifocal contact lenses are not as successful as conventional single- vision contact lenses and thus may not be useful for some people. The most frequent visual problems with bifocal lenses are fluctuating distance vision and poor near vision. Rigid gas- permeable lenses give better image quality than hydrogel (soft) bifocals.

Trifocals-Individuals who have difficulty seeing well at an intermediate distance (3-5 feet away) with bifocals may need trifocals, which have a middle section to correct for midrange distance. A person wearing trifocals looks through the top segment to see distant objects, through the middle to see just past arm’s length and through the bottom to see close objects.

Your eye doctor and optician can suggest the right kind of reading glasses for you, depending on your occupation, hobbies and visual needs.

“Eye Facts” is an informational series and should not be used as a substitute for medical advice. For eye appointments, call (312) 996-6591. All Eye Facts illustrations and images are copyright protected and are the property of the UIC Board of Trustees. Unauthorized use of the images is prohibited. For usage of any Eye Facts content or illustrations please contact the Office of Medical Illustration at eyeweb@uic.edu or 312-996-5309 for licensing.
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