Which Eyeglasses Are Right For You? Bifocal, Progressive or Single-Vision Reading Glasses?
It’s great being over 40.
No, 40 is not really the new 20. That’s because at 40 you really begin to come into your own, personally and professionally, unlike when you’re 20. It’s in your 40s when you start to figure out who you really are. Sure, you’ve made some mistakes. Who hasn’t? But now that you’re over 40 you find you’re actually learning from your mistakes, rather than making the same ones over and over again.
But just at the point you start to hit your stride, you also start noticing that physically, certain things don’t work as well as they used to.
Like your eyes, for example.
It used to be that when you were younger, whether you were nearsighted, farsighted or had perfect vision, your eyes could adjust to see things both far away and up close, whether you were looking through prescription eyeglasses or not. But now that you’ve entered your fifth decade, a curious thing happens. You notice you’re not able to see things up close as well as you used to.
Reading an instructional manual? No way.
The directions on a pill bottle? Fuggedaboutit.
Now you find yourself constantly moving what you’re trying to read back and forth, back and forth, as you attempt to find the exact position where you can see it clearly. You do this so much you start to feel like a trombone player.
You don’t want to admit it, but you know it’s true. It’s time to start thinking about multifocal glasses. Or at least reading glasses.
But what should you get? If you already wear glasses to correct nearsighted or farsighted vision, the first thing that probably pops into your mind is bifocals. But what enters your mind right after that is grandma, rocking and knitting and watching “Matlock.”
That’s not me, you say to yourself. I don’t want people looking at me, seeing that line on my glasses and thinking, “Out to pasture.” You’ve heard there are such things as no-line bifocals, or multifocal glasses, called progressives, but you’re not sure about them. You’ve heard that some people have a hard time finding their visual sweet spot.
So you consider separate pairs of glasses, for distance, computer, and reading vision. But if you wear corrective lenses already, you might not want to have to worry about using multiple pairs of glasses. “Glasses strewn all over the house?” Uh-uh. “Reading glasses on a chain?” Even more emphatically: Uh-uh. Once again the dreaded image comes to mind: Grandma.
Don’t worry. You’re not your grandma. You’re years away from the early bird special at Denny’s. All you need is a little help with your presbyopia.
My what? OK, we’ll explain. When you’re young and your eye muscles are elastic, they easily expand and contract to allow the lens of your eye to change shape to enable you to see objects clearly at various distances.
This process is called accommodation.
But after your eye muscles do this for about 40 years, they get a little tired and stiff, just like your other muscles. Consequently, no longer can your eye muscles so easily expand and contract to enable the accommodation process.
This condition is called presbyopia.
If you have it, and once you hit your 40s there’s no way around it, you’re going to need some kind of reading magnification power. So let’s look at the various options to see which is right for you.
Again, if you already are wearing corrective eyeglasses, multifocal lenses will most likely be your best option. So let’s start with bifocals.
The invention of bifocals is credited to Benjamin Franklin, who ingeniously took one pair of glasses with a distance-vision prescription and another pair of glasses with a near-vision prescription. He cut each lens in half horizontally. Then he put the two pairs of glasses together, with the distance-vision lens half on the top and the near-vision lens half on the bottom. Voila: bifocals.
Bifocals come in various styles. At Zenni Optical we offer the most popular bifocal lens style, the flat-top 28 bifocal (FT 28). This means that, unlike some bifocals with a round, near-vision (reading-vision) segment lens, the flat-top bifocal is in the shape of a D turned on its side, with the flat part of the D facing up and the curved portion at the bottom. Because of this, it’s also known as a D segment lens. The 28 comes from the width of the bifocal lens, roughly 28 millimeters across.
It’s important to know that, at Zenni Optical, the bifocal segment lens starts two millimeters below the center horizontal line of the lens. So if you select a lens with a height of 30 millimeters (the minimum lens height necessary to accommodate a multifocal prescription at Zenni), the bifocal segment lens will go from the bottom to 13 millimeters up from the bottom. That’s half of the lens height, 15 millimeters, minus two. If you select a lens with a height of 36 millimeters, your bifocal lens will start at 16 millimeters up from the bottom. That’s 18 (half of 36) millimeters minus two.
People who like bifocals prefer having their distance and near vision clearly separated by a visible line. They don’t care, or are less concerned about, what this implies about their age. However, people who don’t like the way bifocals correct their vision complain about the phenomenon known as “image jump”, which refers to the abrupt switch from distance to near vision, which can be disorienting.
Presbyopes who want a smoother blend between distance and near vision tend to prefer multifocal lenses with no visible line separating the larger distance portion and the smaller near segment. These invisible line bifocals (or, more accurately, multifocals) are called progressives.
That’s because the vision “progresses” from distance to near vision with no image jump. In addition, in between the portion of the lens with distance vision and the portion with near vision, there is a portion of the lens that provides intermediate or computer vision.
Let’s look at these no-line multifocal lenses a little more closely. Progressives could also be called no-line trifocals, because there are three fields of vision in the lens with no visible line separating them. This is great for disguising your need to wear “old people’s glasses” but it comes at a cost. Literally, since progressive eyeglasses are, as a rule, more expensive than single-vision or bifocal glasses. But there’s also an aspect to pay attention to in terms of the amount of vision correction on the lens.
The reading-segment lens of bifocals is, as we noted, roughly 28 millimeters across. But with progressives, the reading segment lens is about half that, roughly 14 millimeters across. In addition, there is no vision correction on either side of the reading portion of the lens.
To get a sense of how a progressive lens is configured, think of a mushroom.
Here’s a good mushroom image:
Imagine the cap is the distance-vision section of the lens. Think of the mushroom’s stem as the intermediate and reading portion of the lens, around 14 millimeters wide. People who prefer the wider reading segment provided by bifocal lenses often feel that the progressive lens doesn’t provide a wide-enough near-vision reading corridor.
At ZenniOptical.com we offer a few ways to customize a pair of progressive glasses for your preference when you order glasses online. For example, we ask questions to help us create the right progressive correction for your needs.
The first question we ask is, “What is your primary use for these glasses?” The choices are “General / Office” (the most common) and “Sports, Outdoors or Driving”. If you select General / Office, your lenses will have expanded distance and reading portions and a narrow intermediate (computer) section. If you select Sports, Outdoors or Driving, the lens is optimized for outdoor use. It has an increased distance and intermediate section but a smaller reading section.
The next question we ask is, “Where will you wear the glasses on your nose?” You have three choices: high on my nose, middle of my nose or low on my nose.
If you choose “high on my nose” the progressive section of the lens will begin at the exact horizontal midpoint on the lens. Again, with a lens height of 30 millimeters, the intermediate (computer) vision section will be at 15 millimeters up from the bottom. However, if you select either middle or low, the intermediate (computer) vision section will be at 17 millimeters up from the bottom, meaning two millimeters about the center horizontal line.
This is the opposite of bifocals, where the correction starts two millimeters below the center horizontal line.
Progressives won’t work for everyone, though. Some people respond adversely to the lack of a visible line separating the three focal fields, to the point of feeling dizzy or nauseous while wearing progressives. For most first-time progressive eyeglasses wearers, this goes away in a few minutes or a few days.
For some people, however, the discomfort they feel wearing progressives never goes away. Moreover, wearing a pair of multifocal glasses, bifocals or progressives, can be dangerous for some people, according to research published by Investigative Ophthalmology & Visual Science. This study found that people wearing either bifocal or progressive glasses are more than twice as likely to fall when wearing multifocal glasses than they are while wearing single-vision glasses. This increases if the wearer is walking downstairs.
People who feel they might have a hard time maintaining their balance while wearing multifocal glasses, or who have tried and dislike bifocals and progressives, would very likely do better with separate pairs of single-vision glasses for distance, computer and reading vision.
Single-vision distance glasses are used for seeing distances roughly two feet away or more. Single-vision intermediate (computer) glasses are used for seeing distances between one-and-a-half and two feet away, basically how far away a person usually is from a computer screen. Single-vision near (reading) glasses are used for seeing objects six inches to one-and-a-half feet away, roughly where you would hold a book you are reading.
For single-vision distance glasses, all that is needed are the plus or minus numbers in the Sphere (abbreviated SPH), Cylinder (CYL) and AXIS sections of a prescription. Ignore the plus number (it will be the same for both eyes) in the NV-ADD (Near-Vision reading ADDition) section of your prescription till you are ordering intermediate and reading glasses.
For single-vision reading glasses, it’s a little more complicated, although it just requires a bit of grade-school arithmetic. Take the plus number in the NV-ADD section of your prescription and add it to the numbers in the SPH section. For example, if you have -1.00 in your SPHs, and +2.00 in the NV-ADD, when you add these two numbers together, you end up with +1.00 in the SPH section. That gives you near single-vision.
Remember, if you are ordering single-vision reading glasses, you will need to lower your distance vision pupillary distance (PD). Your PD is the measurement, in millimeters, between the middle of one pupil to the center of the other.
If you have a single PD number, which would be one number between 50 and 75, subtract three. For example, let’s say your distance vision PD is 63. Lower this by three, to 60, for single-vision reading glasses.
However, you may have a dual PD, which is the measurement from the center of each pupil to the center of the bridge of your nose. In this case, you would have two numbers, each somewhere between the mid-20s to the mid-30s. These two numbers should add up to the single PD number. For example, if you had a dual PD of 31.5 in the right eye and 31.5 in the left, your PD would add up to 63. Therefore, to get your near-vision dual PD for single-vision reading glasses, you would lower each eye’s PD by one-and-a-half, since combining two of that number adds up to three. That would be 60, just as it is if you have a single PD.
For single-vision intermediate (computer) glasses, if you take your NV-ADD number and divide it in half (+2.00 divided by 2=+1.00), then add that to your -1.00 SPHs (+1.00 + -1.00=0.00), you get your intermediate (computer) single-vision. You don’t have to change the PD at all, but you could lower it by one or two millimeters, if you have a high PD (over 66).
If you want to use a pair of bifocals to reconfigure your prescription to get computer vision in the top part of your lens and reading vision in the bottom, do the same thing you would do for single vision computer glasses.
Divide the NV-ADD in half and add this half number to the SPHs. But this time, leave the remainder in the NV-ADD section. That’s how you would get computer vision in the top part of the lens and reading vision on the bottom.
It’s as simple as that.