If you're a glasses wearer, you need to think about more than just the numbers on your prescription. There's also something equally important, but perhaps less well-known, that you might not have heard of. That's the measurement called Pupillary Distance, or 'PD' for short. Let's take a look at what it is, why it's so important, and how to measure it at home.
Simply put, what is Pupillary Distance (PD)?
Pupillary Distance (PD) is the distance between the center points of the two black rings (pupils) in your eyes. It is measured in millimeters (mm). It is sometimes called ``Interpupillary Distance - ID''.
Imagine, when you are getting glasses made, you need to adjust the lens so that the highest power point is exactly in front of your iris. Otherwise, you will not see clearly. This is where the PD measurement is essential to make the correct adjustment. If you are buying glasses online, you will definitely need this PD measurement along with your prescription.
How to measure your PD at home?
The best way to actually get this measurement is to have it done by a trained professional, such as your eye doctor or an optician, because that's the most accurate method.
However, if you want to measure yourself, there are ways to do that too. All you need is a measuring tape marked in millimeters (mm) and a mirror. Sometimes you can find special measuring tapes or even smartphone apps designed for this purpose. But keep in mind that the accuracy can be a bit off when you measure yourself or with an app.
If you want to measure yourself...
If you're doing this alone, you need to be a little careful. Follow these steps.
| Steps | What to do |
|---|---|
| 1. Preparation | In a well-lit area, stand in front of a mirror about 18 inches away. |
| 2. Placing the footrest | Turn the millimeter markings on the tape measure so that they are visible in the mirror, and hold them under your eyes and above your nose. As if you were peering over a wall. |
| 3. Right eye measurement | Close your left eye. Using only your right eye, place the zero (0) mark on the ruler exactly in the middle of your right eye's black circle. Do not move the ruler from this point on. If it does, start over. |
| 4. Measuring the left eye | Now open your left eye and close your right eye. Looking only through your left eye, see which millimeter mark is directly in the middle of your left eye's black circle. |
| 5. Taking the measurement | The millimeter value you find will be your PD measurement. |
If you measure with someone's help...
This is easier than doing it alone. The person helping you should do it this way.
| Steps | What the helper should do |
|---|---|
| 1. Preparation | Sit in front of the person you want to measure, about 18 inches away. Keep both of your faces at the same level. |
| 2. Placing the footrest | Place the foot under the other person's eyes and above their nose. |
| 3. Right eye measurement | Ask the person taking the measurement to look straight into your (the person helping you) left eye . Place the zero (0) on the measuring tape at the outer edge of the black ring of the other person's right eye. Do not move the measuring tape from this point on. |
| 4. Measuring the left eye | Now ask the other person to look straight into your right eye . Now see which millimeter mark corresponds to the inner edge of the black ring on their left eye. |
| 5. Taking the measurement | That millimeter value you see is his PD measurement. |
Why is this PD measurement so important?
You know, we see things when light enters the eye. This light enters the eye through the pupil. Then that light passes through the lens and is focused on the retina.
But if you have poor eyesight, this light doesn't focus properly. That's why we see blurry. For example:
- Farsightedness/Hyperopia
- Nearsightedness/Myopia
- Difficulty seeing near as you get older (Presbyopia)
- Astigmatism
Eyeglasses are not one-size-fits-all. They vary depending on many factors, such as your vision problem and the strength of your prescription.
This PD measurement must be accurate in order for the power of the lens of the glasses to be focused exactly on the center of your iris. Only then can you get the most out of the glasses and see the world clearly.
Imagine what would happen if the PD measurement was wrong...
If the glasses you use are made for the wrong PD measurement, you will definitely start to feel it.
- Eyestrain
- Headache
- Visual distortions (seeing things as if they are stretched)
Although these symptoms are not dangerous, they are very uncomfortable. Furthermore, the continued strain on your eyes can actually worsen your vision.
The average adult PD is about 63 mm. However, it can range from 50 to 70 mm. It varies from person to person. Your PD may change as you grow as a child, but it usually doesn't change as you grow into an adult. However, very rarely, it may change slightly after facial or eye surgery.
When is it not appropriate to measure your PD yourself?
If you usually use your glasses for a single purpose (e.g., reading), getting your own measurements may not be a big deal. However, there are some special cases where you absolutely need a professional-level measurement . Trying to get your own measurements is not a good idea at that time.
| Opportunity | Reason |
|---|---|
| If you need multifocal lenses | These are also known as ``Progressive lenses, bifocals, trifocals''. These lenses have different powers in several parts. Therefore, if the PD measurement is off by even a millimeter, vision can be completely distorted. |
| If you need to wear glasses all the time to see both near and far | When we look at something close, our PD decreases by about 3 millimeters. This difference must be considered when designing glasses like this. Accurate measurement is essential for this. |
| If you have any misalignment in your eyes | Medically, this is called ``Strabismus.'' In this case, separate measurements must be taken for each eye and the glasses must be made very accurately. |
Some countries have laws that require PD measurements to be included in your eyeglass prescription. Although there is no such law in our country, you can always ask your eye doctor or optician for your PD measurements. It is your right.
Take-Home Message
- Pupillary Distance (PD) is the distance between the black rings of your eyes. This measurement is essential for getting the right fit for your eyeglasses.
- Wearing glasses made for the wrong PD measurement can cause eye strain, headaches, and blurred vision.
- While you can take this measurement at home, the most accurate and safest method is always to have it measured by a professional.
- Be sure to get a professional measurement, especially if you use multifocal lenses or have a condition like strabismus.
- If your prescription doesn't include the PD measurement, don't be afraid to ask your doctor or optician about it.
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