Presbyopia: What is it, and What are the Options?
No one wants to look older, but most people find that aging does cause many changes to deal with as our bodies adapt to the passage of time. When we hear our eyecare practitioner say the word “bifocal,” we are sure we’ve reached whatever is on the other side of youth and vigor.
You are not alone.
The inner crystalline lens, located behind the iris, is one of the only types of tissue in the body that continues to grow with each passing year. Eventually, it gets to a point where the muscles we use to change its shape are no longer effective; it isn’t that the muscles are getting weaker, it’s just that the lens has reached the point where it is too stiff to respond. This usually happens at age 40 or so; we call this condition presbyopia. This condition is nearly universal, making it difficult to see small print without the help of lenses to help us bring reading material into focus.
It has been estimated that about one-half of the population of Canada and the US under the age of 40 have refractive errors, which include nearsightedness farsightedness and astigmatism. Presbyopia is a separate type of refractive error which develops over time in addition to these three. Most people in Canada and the US choose to wear spectacle eyewear or contact lenses to provide themselves with clear vision.
Presbyopia is not corrected with LASIK or other refractive surgery. A person who has refractive surgery in his or her 20s will still become presbyopic and will need to use some type of reading correction at the age of 40 or so. There is currently no surgical procedure that will correct presbyopia.
People who are entering presbyopia have several options to restore their ability to read clearly with spectacle lenses:
- Single-vision reading glasses
- Bifocal or trifocal lenses with lines
- Progressive addition lenses without lines
Benjamin Franklin is widely credited with inventing the first bifocal lenses when he began to need a pair of glasses for reading, in addition to those he needed to see clearly in the distance. He found switching from one pair of glasses to the other so irritating and annoying that he cut the bottoms from his reading lenses and placed them into the same eyeglass frame as the tops of his distance lenses, thus enabling himself to see clearly down the street, while still allowing him to see his reading materials clearly without having to switch back and forth between the two.
Whatever they are called, multifocal lenses are simply a convenience item. They are not meant to make your life difficult at all; on the contrary, they are meant to make things easier.
The purpose of a multifocal lens is to put more than one lens prescriptions in the same eyeglass frame. In presbyopia, they are used to put the distance power in the top and the near power in the bottom, for uninterrupted clear vision.
Contact lens wearers have other options; for more information, see our article titled “Contact Lenses in Presbyopia: Monovision”.
Most eyecare practitioners recommend Progressive Addition Lenses (PALs), a modern multifocal design that gives clear, comfortable vision for distance, intermediate and near. A progressive lens (PAL) is designed to add power gradually, from the optical center of the lens to the full power for reading, without any lines or visual “jump” from distance vision to near and back.
Most people find PALs to be a natural, easy way to see clearly at any distance. As the eye moves naturally from straight-ahead gaze, dropping to look through the reading area of the lens, the transition is automatic, and without effort. Most people find they have no difficulty in adapting to progressive lenses at all, because of the gradual change in power
Single Vision Reading Lenses
Some people, especially those who have never used any type of eyewear to see clearly think that perhaps single-vision reading glasses are the best option. Single vision readers have just the reading prescription, without any type of multifocal. While single vision reading lenses are probably the least expensive option for those entering presbyopia, it is important to understand that, while these will give clear vision for reading or using a computer, they will also cause distance objects to be blurred.
For example, someone wearing reading lenses can usually see a computer monitor and their desk top quite well, but when they look up across the room to check on the time, for example, the clock will be blurry. To see clearly in the distance, they must either remove their glasses or look over the top of them.
Many of us have seen reading glasses for sale on racks in discount stores or department stores that can be purchased without a prescription. Most people will benefit more from lenses made just for their unique vision, not a just pair of glasses made from “one-size-fits-all” prescriptions in inexpensive frames that will not stay in proper adjustment on the face.
Multifocals: Bifocals and Trifocals
In the past, a multifocal lens came with a small “window” molded into it that allowed the prescription power to be different there than in the rest of the lens. This type of lens is called a flat-top or a line- bifocal; the window in the lower part of the lens is usually available in several widths, 25 mm, 28 mm and, less common 35 mm. The power in the window of the lens is known as the add power.
As an example, someone aged about 45 might need an add power of around +1.50, while someone older, at age 65 will probably need an add of +2.50. It is normal for the amount of the add power necessary to increase from age 40, but it will usually stop at about +2.50, because that is the power needed to focus at a distance of about 16 inches.
Sometimes, line bifocals, cannot make the intermediate distance clear. For example, someone playing cards might see across the room and at the cards in his or her hand, but not across the table at a partner or at cards played on the tabletop. A trifocal usually has a power in the middle part of the lens that is half that of the bottom part.
Presbyopia is Natural
The onset of presbyopia is not cause for alarm. The inability of the inner lens to respond to changes of focus does not mean you are losing your vision, nor does the use of any multifocal lens or single vision readers cause the eyes to get worse. Also, the use of a multifocal lens has nothing to do with how “bad” or “good” your vision may be; the multifocal is just an easier way of dealing with these normal changes than to constantly have to change glasses back and forth between distance and near. Convenience is the only reason multifocal lenses exist.