Your doctor doesn’t always specifically mark what type of prescription lens you should order, but you have options and you should know about them.
Types of Prescription Lenses
There are several different prescription lens types and, within them, several subtypes of lenses. If you are shopping for prescription glasses online and you’re not sure what the different lens types are, you’re not alone. We get calls every day with customers asking us what type of lenses are appropriate for their prescription.
The different lens types are simple to understand even if the optics behind them sometimes gets very complicated. If you’re wondering what the different lens types on our web site mean, here’s what you should know:
- Single vision lenses do not contain any sort of bifocal. They are the same prescription throughout the lens, and they are most often used for distance prescriptions (although you can get them in near or reading prescriptions as well).
- Lined bifocal lenses are often referred to as FT-28 or FT-35. They have your distance prescription on top and a separate semicircular area for reading on the bottom. This is the lens most people think of when they hear the word “bifocal.” When you enter your prescription into our form, your bifocal power is often marked as “ADD” or “Addition,” and it is almost always the same for both eyes.
- FT-28 and FT-35 are describing the bifocal section itself. “FT” stands for Flat Top, which is describing the semicircle shape of the lens, which is flat on the top. The “28″ and “35″ are describing the width of the semicircle. FT-28′s are 28mm wide, and FT-35′s are 35mm wide.
- Progressive bifocal lenses have a reading area on the bottom, but your lens progressively goes from distance to reading as you go from the center of the lens to the reading area. Most bifocal wearers nowadays use these. Just as with lined bifocals, your reading strength is marked as “ADD” or “Addition” and usually is the same for both eyes.
- Your prescription will have several sections. The distance portion is marked as OD and OS (for right and left eyes, respectively) and there are three types of correction for each eye: Sphere, Cylinder, and Axis.
- Sphere is the correction for nearsightedness or farsightedness.
- Cylinder and Axis work together and correct for astigmatism.
- If you are getting a bifocal, there is a measurement called Segment Height that you may be unfamiliar with. This is the millimeter distance from the bottom of the lens to the start of the bifocal. For a lined bifocal, it is typically set at a standard height or measured from the bottom of the lens to the top of your bottom eyelid. For a progressive lens, it it typically measured from the bottom of the lens to the center of your pupil as you gaze straight ahead. Segment height is different for every frame you wear.
- Pupil Distance, or PD, is the millimeter distance from one pupil to the other. Sometimes is it marked from the center to each eye; in this case, the OD right eye is always marked first. Some doctors also mark your “distance PD” and “near PD.” This is because your PD is slightly different when you’re reading because your eyes converge, or cross, toward each other when you look at something close up, bringing your pupils a few millimeters closer together.
If you are in the market for prescription glasses, your choice of lens type should be based on what you’re going to use the glasses for. For instance, if you normally wear a progressive bifocal but need motorcycle or sports glasses, you may want to skip the bifocal and go with single vision if you don’t think you’ll be reading at all with the glasses.
Most people with bifocals have certain situations where they may get single vision because they’re ordering glasses for a specific use that will not require reading. Single vision wearers, on the other hand, do not ever go with a bifocal because there is no instance where they’d need it.
If you have any more questions about lens types, or if you’re wondering which is best for you, you can leave a comment in the comments section below, or you can call or email our customer service department. Thanks for reading, and happy shopping!