Presbyopia: When Things Up Close Are Out of Focus
As predictably as the sun rises in the east and sets in the west, age alters people's ability to see clearly. Presbyopia—or the inability to focus sharply on nearby objects—is not a new phenomenon. Aristotle first noted it more than three centuries BC. "It's a fountain of youth thing," says Seattle ophthalmologist Richard Bensinger, MD, a spokesperson for the American Academy of Ophthalmology. "We'd love to be able to not run into presbyopia. But it's very predictable."
What Causes Presbyopia?
At birth, the crystalline lens of the eye has a high degree of flexibility and elasticity that enables it to change shape and focus on items at a wide range of distances. With the passing years, however, the proteins in the lens become solid, the lens becomes harder, and the muscles surrounding the lens weaken. These physical changes are accompanied by a decrease in "accommodation," the ability to change the focus of the eyes as the distance to an object becomes closer. Accommodation decreases until a point—typically in a person's 40s—when it becomes impossible to clearly see things within a closer range of distance.
Most people, often subconsciously, start making subtle adjustments to this developing inability to accommodate. People who have never worn glasses may find themselves holding items at arms length or turning up the lights to make images sharper. People who are nearsighted may find themselves taking off their glasses to see things that are close.
"Most people deal with presbyopia by getting bifocals, trifocals, or progressive lenses," says optician Arthur Chikofsky, ABOM, adjunct lecturer at New York City Technical College.
Some people who never needed glasses or those who had laser surgery to correct nearsightedness can get by with over-the-counter reading glasses, according to Dr. Bensinger. However, over-the-counter glasses are made only for the "average" person, so it is best to see an eye doctor for a prescription. Furthermore, optical shops offer a better selection of frames, and professional vision exams aid in determining the correct lens strength and fit. Most importantly, everyone should get regular eye examinations to check the health of the eyes, as many eye diseases are "silent" and do not have symptoms until very advanced.
Bifocals And Trifocals
Linda A., of Buffalo, New York, is nearsighted and resists the suggestion of bifocals, so she instead takes off her distance glasses to read. Other people have one set of glasses for near and one for far. Ben Franklin considered this too inconvenient, prompting him to invent the bifocal by putting two pieces of glass with differing corrections in one frame.
Some people still choose this type of traditional bifocal, but most consumers opt for progressive lenses. Besides looking a bit old-fashioned because of their telltale "line," bifocals only correct to two distances. Trifocals add a third, intermediate distance, but anything in between can appear blurry. To read or see things that are near, you must look down.
Progressive lenses, developed during the 1950s, eliminate the traditional bifocal line, while providing a smooth transition between corrections. As you look down the lens, images that are closer and closer are brought to focus. So, you might look halfway down the lens to look at your computer, but all the way down to read a magazine. Many consider the lenses worth the additional expense because the vision is better and no one can tell they're wearing bifocals.
"The [best] reason for wearing progressives has to do with the field of vision," says Chikofsky, who explains that current progressive lens products can match the eyes' ability to see a range of distances clearly. It takes about a week before people fully adjust to the lenses, and they must employ subtle head movements to bring items into focus. Some people are not able to get used to progressive lenses, so they usually choose bifocals or trifocals instead.
"The eyes naturally fall into the right spot in the lens," Chikofsky says. "When starting out, you point your nose at what you want to see and bring your chin up and down a little to get it crisp. Eventually, your eyes find the right spot and people completely forget they are wearing a bifocal."
Options are available for the many contact lens users who get presbyopia but don't want to use reading glasses in addition to their lenses.
- Monovision contacts: With the contact lens in the dominant eye correcting for distance and the lens in the other eye providing clear near vision, monovision contacts work for about 60%-70% of those who try them. It sometimes takes a few days to get used to them.
- Bifocal contacts: While bifocal contact lenses can help you see at distance and near, many patients have difficulty using them. Furthermore, night vision is typically not as good as the night vision you'd get from wearing regular contacts or glasses.
- Modified monovision lenses: These lenses give the dominant eye a distance correction and the other eye a bifocal lens. Another possibility involves wearing different strength bifocal lenses in each eye, with one lens more for far and the other more for reading.
Although laser surgery has become a popular way to correct refractive problems, there are currently no laser techniques to correct presbyopia because current laser surgery can only focus the eye at one point.
However, doctors can create permanent monovision. Dr. Bensinger lets patients try monovision contact lenses before operating to ensure that they can adjust to one eye seeing near and the other seeing far. This is important, he says, because laser surgery is not reversible.
Another option, conductive keratoplasty, is a surgery that uses a small probe to change the shape of the cornea in one eye to focus it for near. If the other eye is well focused for distance, you will have monovision correction.
Probably the hottest topic in presbyopia correction is "multifocal" and "accommodating" intraocular lenses. When a person has ]]>cataract]]> surgery, the ophthalmologist places a lens inside the eye to replace the cloudy lens that is removed. These lenses are usually just focused for distance, so most patients still have to wear reading glasses (and sometimes distance glasses) after the surgery. Some eye surgeons focus one lens for distance and one for near, giving permanent monovision, but that has some drawbacks as well.
Accommodating intraocular lenses can move inside the eye giving some range of vision, although the range is usually limited. The newly developed multifocal lenses have two focal points, one for distance and one for near, thus giving excellent distance and near visual acuity with both eyes.
There is a slightly increased risk of side effects with the multifocal lens, so it is important to discuss the risks, benefits, and alternatives in detail with your ophthalmologist. While these multifocal lenses are usually only placed at the time of cataract surgery, some surgeons will perform what is called a "refractive lens exchange," which removes your lenses before cataracts develop and place a new, usually multifocal, lens in its place. Another drawback to multifocal lenses is the cost. While most insurances pay for cataract surgery, the patient is responsible for the extra cost of these "luxury" lenses.
Making a Decision
While surgical options may be on the horizon, most people continue to opt for glasses. Before you notice that your arm has become a tad too short to hold things where you can focus on them, make an appointment for an eye exam with an ophthalmologist or an optometrist, who will refer you to a licensed optician to have your glasses or contacts made.
Tell the doctor who is writing the prescription and the optician filling it what your specific needs are, including hobbies and occupational sight requirements. Your eye care professionals will help you make wise decisions about the corrective options that will work best for you.
If you decide on a surgical option, do your research. Ask your ophthalmologist for detailed information on the surgery, including the risks, benefits, and alternatives.
American Academy of Ophthalmology
National Eye Institute
Canadian Health Network
American Academy of Ophthalmology website. Available at: http://www.aao.org .
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Last reviewed January 2009 by ]]>Eric L. Berman, MD ]]>
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