How to Read a Bifocal Prescription
Dr. Jordan Marr
If you wear reading eyeglasses, you will know all too well how inconvenient it can be to always carry them around in case you need to read something. This will especially be the case if you also wear glasses to correct your distance vision. Bifocal lenses are a great solution for anyone with a reading prescription who is looking for a more convenient option.
However, bifocal prescriptions are a little bit different to a regular eyeglass prescription. All those numbers and letters may seem daunting at first, but it’s much easier to read a bifocal prescription than you may think!
What is a bifocal prescription?
A bifocal prescription is a specialized eye prescription that has two sections; one to correct your distance vision, and one to correct your near vision.
The up-close portion of a bifocal lens is called the segment, which can come in different shapes (such as round top or flat top). The segment sits in the lower part of the lens and is surrounded by the distance portion of the lens. This means that when you are looking straight ahead or through the top of your lens, you will be able to see far away. When you look down (through the segment) you will be able to see nearby objects and read clearly.
You might wonder why a bifocal is designed this way. When we do up-close tasks (such as reading) we usually look down and when looking at something far away we are usually looking straight ahead or upwards. For this reason, bifocal glasses are designed to have the reading prescription lower in the lens and the distance prescription higher up. This allows for you to swap between the two prescriptions more comfortably and adds to the convenience of a bifocal lens.
If your eye doctor gives you a bifocal prescription, it will include details for your distance prescription (i.e. sphere, cylinder, and axis) as well as your reading prescription (i.e. add).
Here’s an example of what a bifocal prescription may look like:
In the right eye, the sphere power is +1.00 and the cylinder power is -0.75 situated at 90 degrees (axis). This is the distance prescription. This person has a +2.00 add, which is the extra magnification needed in the reading segment of the bifocal. The pupillary distance (PD) is 64mm for distance and 61mm for near vision. This is how far apart your pupils are from one another.
We’ve written more elsewhere about the process of getting an eye prescription and reading a prescription!
How is a bifocal prescription different?
Bifocal prescriptions are different to a single vision prescription, which can only correct your vision at one distance (i.e. up close, far away, or intermediate). When getting bifocals, you will also need to take a height measurement.
The fitting height for a bifocal lens measures from the bottom of the lens to the top of your lower eyelid and marks where your reading segment will begin. For example, a fitting height of 15mm will mean that your reading zone begins 15mm above the bottom of the eyeglass lens.
In a progressive lens the prescription is the same as that of a bifocal, however the fitting height will be at the pupil instead of the lower eyelid. This is because progressive lenses transition from distance (at the top of the lens) to intermediate and finally to reading (at the bottom of the lens).
What are bifocals for?
Bifocals are for people who need eyeglasses to see both nearby objects and far away objects, or people who wear reading glasses but would rather not constantly put them on and take them off. Bifocal lenses are a convenient option that allow you to wear one pair of glasses all the time.
Some of the benefits of bifocal eyeglasses include:
- ConvenienceHaving one pair of glasses for everything prevents you from switching between multiple sets of eyeglasses to perform different tasks.
- Cost-effectiveBifocal lenses are considerably cheaper than progressive lenses, while still offering the ability to see up-close and far-away simultaneously. Additionally, it is more cost-effective to purchase one set of bifocal glasses than two pairs of single vision glasses.
- Easy to adapt toMany people consider bifocal lenses easier to adjust to than progressive lenses. This is because there is no soft-focus area in a bifocal and there are only two zones to look through. This decreases feelings of dizziness, headaches, and nausea that may be associated with adjusting to progressive lenses.
However, nothing’s perfect! Here are some of the drawbacks of a bifocal lens:
- Distracting lineSince there are only two prescriptions in a bifocal, there is no smooth transition between the distance and reading zones. Instead, there is a harsh line separating the near segment from the rest of the lens. This can be distracting at first as you might notice a “jump” in prescription if your eyes move too drastically in the lens.
- Adjusting to bifocalsAs with anything, it takes time to adjust to a new lens design. Although bifocal glasses are much easier to adapt to than progressive or multifocal eyeglasses, there is still an adjustment perio. When you first get your bifocals, it will take some time to train yourself to look through the correct part of your lens. This can sometimes cause headaches and nausea, but typically does not last long.
Can prescription sunglasses be bifocal?
Yes! Bifocal sunglasses are a great option for people who want protection against glare and UV rays whilst also being able to read while they’re outside. Bifocal sunglasses are also helpful while driving as they allow you to see the road and the dash clearly at the same time.
You can also get transition bifocal lenses, which go dark outside and return to clear indoors. This is particularly useful for people who want one pair of glasses that will do everything! We’ve written more about transition lenses here.
How much do bifocal glasses cost?
Bifocal eyeglasses are more expensive than regular single vision lenses as the manufacturing process is much more complicated. However, buying a pair of bifocal lenses is typically more cost-effective than purchasing two separate pairs of single vision glasses (i.e. one distance and one reading pair).
Despite being more expensive than single vision eyeglasses, bifocal glasses are considerably more cost-effective than progressive lenses, which can cost hundreds of dollars on top of the frame cost.
The price of bifocal lenses varies depending on factors such as lens quality or the brand name. Your prescription may also impact the price of your bifocals, if you need your lenses thinned down or if you would like additional coatings (such as anti-reflective or blue-block coatings).
You can usually find bifocal glasses for much cheaper online than they would be in an eyewear store.
Are there bifocal contacts?
Bifocal contact lenses contain two prescriptions within the one lens, which allows you to see nearby and far away objects simultaneously.
Many different bifocal contact lens designs exist which have different regions dedicated to distance and near vision. This means that you can get bifocal contact lenses that are more tailored to your lifestyle and visual tasks.
You can also get multifocal contact lenses which have a range of powers for different viewing distances and provide a smoother viewing experience.
So… Should you get bifocals?
Before getting bifocals, you should consider what you want to get out of your eyeglasses. If you are looking for a convenient solution to correct your distance and reading vision simultaneously, then bifocal glasses are a great option!
- “Bifocal Add: Image Jump and Image Displacement”, American Academy of Ophthalmology
- “Multifocals”, The Canadian Association of Optometrists
- “Adaptation to Progressive Additive Lenses: Potential Factors to Consider”, Scientific Reports
- “Bifocal Contact Lenses”, University of Michigan Health