Useful Tips

How to measure center distance (PD)?


The correct wearing of glasses depends on the selection of lenses and frames. Interpupillary distance allows you to determine the centering of the lens relative to the pupils of the patient. For this, the doctor determines the distance, enters the data in the prescription. Measurements can be carried out at home on their own, but the ophthalmologist’s accuracy will be higher.

What is interpupillary distance

While wearing glasses, some people have complaints of headache, poor health, eye pain, dizziness. Points may not be suitable for the following reasons:

  • violation of the length between the centers of the lenses,
  • asymmetric face
  • Vertex distance selection
  • wrong glasses.

Determining interpupillary distance avoids some problems. The doctor writes the indicators in the prescription, when selecting glasses, the pharmacist will pay attention so that the center of the lens coincides with the center of the pupil.

Interpupillary distance - the gap between the pupils. Pupils can be located asymmetrically, therefore, ophthalmologists have the concept of a binocular and monocular gap:

  • Monocular distance is measured from the center of the nose bridge to the center of the pupil.
  • Binocular - a segment between the pupils. The binocular segment is equal to the sum of the monocular measurements.

In adults, indicators rarely change over time; in children, new glasses should be selected as they grow.

How to measure PD yourself?

For your convenience, below is a graphic instruction on how to measure your PD. Armed with PD and recipe data, you'll find the perfect pair of glasses at iOptika!

Stand 20 cm from the mirror.

Take a ruler with millimeter divisions.

Position it above the eyeballs by placing a ruler parallel to the eyebrow line. Keep your head straight and straight so that the measurements are accurate.

Close the right eye to find the center of the left pupil

Place the ruler zero at the center of the left pupil. It is necessary to determine the position of the zero mark as accurately as possible: the accuracy of the measurement directly affects the final value of PD.

Measure the center of the right pupil

Open your right eye and find the millimeter mark that exactly matches the center of the right pupil, while not moving the ruler or moving your head. You need to look directly in the mirror to measure the distance correctly.

The numerical value in millimeters that corresponds to the center of your pupil is your PD.

It's important to know:

Measure your PD 3-4 times to ensure its accuracy.

Adult PD Range: 54-74mm

PD range for children: 43-54 mm

How to measure PD with a friend?

Face each other at a distance of about 20 centimeters

Point your gaze over your friend’s head.

Your friend will need to crouch or sit in front of you so that he is out of your sight.

Take the necessary measurements.

It is important not to move your eyes while a friend measures the distance between the pupils. To do this, he needs to arrange the ruler as you would yourself if you measured the PD in the mirror. Your friend should compare the zero mark of the ruler with the center of one pupil and determine the opposite of what the center of the pupil of the other eye will be.

Norm indicators

The determination of interpupillary distance has changed. Norms have changed a bit. The methodology for measuring the center-to-center gap has become different, taking into account past errors.

Previously, the gap difference was determined 2 mm for distance and near. Now this indicator varies from 4 to 6 mm. The distance can be recorded with any number, and by old standards the indicator should be even. New recipes are different from the past. So, the distance was indicated separately for distant and separately for close objects with a difference of 2 mm. Now it is generally accepted that indicators can vary up to 7 mm. Modern lenses of complex design determine for a close distance 2.5 mm less for each eye than for the far.

The interpupillary distance norm is considered to be 62 mm, data can be in the range of 54-74 mm. If the segment is fractional, then the result is rounded. With strabismus in the recipe indicate the distance that would be normal in a person.

Is it possible to measure yourself

You can measure the interpupillary distance yourself. This will require a millimeter ruler and a mirror. If there is no ruler, then you can print a special scale for measuring, but first you need to make sure that the printer does not distort the scale.

The room should be well lit. You should stand in front of the mirror at a distance of 20 cm. The ruler should be located above the eyeballs, parallel to the eyebrow line. Keep your head level to get more accurate measurements.

First, close one eye and place zero on the ruler opposite the center of the left pupil. The more accurately the center is determined, the better the result.

Next, open the second eye and find the division on the ruler, which will be exactly in the middle of the pupil. At this time, you can not move your head or move the ruler. Eyes should be directed in a mirror that measurement passed correctly. The data obtained in millimeters are the interpupillary distance. Measurements should be taken 3 or 4 times.

Help of another person

You can take measurements using another person. Following simple rules, you can understand how to measure interpupillary distance with an assistant. To do this, you need to stand opposite each other. The distance between faces should be 20 cm. A larger or shorter interval will lead to a distortion of the result.

The person who is being measured should look above the assistant’s head. It is desirable that the head is lower than the eyes of the subject. You should look at the subject, which is 3-6 meters from the person.

For accuracy, you can not move, move your head and rotate your eyes. The gaze should be fixed. The ruler should be placed above the eyes parallel to the eyebrow line. Zero should be installed in the center of the pupil of one eye and determine how far the other pupil will be.

Ophthalmologist Check

Measuring the interpupillary distance at the optometrist will show a more accurate result. When selecting glasses, the doctor holds a special ruler at different intervals, depending on the degree of myopia or farsightedness.

If the patient suffers from hyperopia, then the distance from the ruler will be 33 cm. The patient should look just above the ruler at the forehead of the doctor. The ophthalmologist closes one eye, and the second looks at the opposite eye of the patient. Thus, the doctor fixes the edge of the limb. Similar actions are carried out with the other eye. Zero division corresponding to the rim of the patient’s eye will become the distance between the pupils.

With myopia, the patient looks at an object that is located at a distance of 5 meters from him. A special ruler will fix zero division opposite the cornea of ​​the left eye and the right. The result will show the space between the pupils. A similar device can be used at home, the instructions are attached to it.


A pupillometer is used to determine the diameter of the pupils, and the distance between them. It is used by oculists. The modern device is rich in settings and guarantees high accuracy of the result. Compared to other methods, pupillometer has the advantages of:

  • fast accurate result
  • definition of each eye
  • uncontrolled movements of the pupils and the degree of illumination of the cabinet do not affect accuracy
  • the result is displayed on the device display.

The device is capable of taking measurements from the bridge of the nose to each pupil. Shows data with asymmetry, farsightedness and myopia. The pupillometer has contraindications:

  1. Curvature of the nasal septum.
  2. Severe visual impairment.
  3. Torticollis.

The ability to measure the distance between the pupils helps to adjust the interpupillary distance when using optical instruments. For some, adjustment is required to see the image.

Interpupillary distance adjustment

Optical instruments, such as binoculars or a microscope with 2 eyepieces, require additional image adjustment. Initially, you should adjust the sharpness and align the instrument horizontally. Observing through the lenses, it is necessary to bring binoculars to adjust the interpupillary distance. The image should become one.

For complex digital devices, you can initially set this distance and complete the image. With the right indicators, it will be comfortable to use the device. The gap between the centers of the lens should coincide with the interpupillary distance.

What is it and why measure it?

Interpupillary or intercenter distance is the length between the pupils. Usually it is indicated in millimeters. Such calculations can be done independently or at a medical institution for consultation with an optometrist. You can determine using a scale or a special device - pupillometer. Ophthalmologists measure interpupillary distance results when prescribing prescription glasses.

How to measure yourself?

To find out the interpupillary distance, it is enough to take a millimeter ruler. If this is not the case, then it is advised to find the scale on ophthalmic sites and print. But before use, it is advisable to check whether the printer has distorted the measurement scale. In some clinics that work online, there is a special program or table that allows you to find out the length at home.

For the measurement procedure, you should stand in front of the mirror, at a distance of 20 centimeters from it. The head should be kept straight, and the meter should be above the eyeballs, parallel to the eyebrows. It’s easier to measure gradually: first you need to cover your right eye and find the zero mark on the ruler with your left. Then open the second eyelid and find the same mark near the center of the right pupil. In this case, it is advisable not to move your head or hands: any movement affects the performance. The resulting length will indicate the interpupillary distance.

Ruler measurement

If you need to select glasses for farsightedness, the doctor keeps the scale at a distance of 33 cm. The patient at the same time looks directly at the ophthalmologist's forehead. He closes the right eyelid with his left eye and looks at the edge of the patient's right limb. So he fixes a zero mark opposite the outer edge of the limb. After that, the ophthalmologist repeats the same actions with the left eye. Zero division of the scale, which will correspond to the rim of the right eye of the patient, and will indicate the distance between the pupils.

The device for selecting glasses for myopia is used in ophthalmology, but it can also be used independently.

If you select glasses for myopia, the optometrist suggests that the patient see the landmark, which is located 5 meters from him. Thus, the pupils fall into the center of the iris. Centering is set by zero division opposite the edge of the left cornea, and then near the rim of the cornea of ​​the right visual apparatus. The distance between them indicates the normal distance between the eyes. Such a device is suitable for use at home: for all explanations, it gives instructions with a full description of the procedure.

In the book “Vision correction. Textbook "N.S. Orlova, G.I. Osipova indicated that this method is inaccurate, because taking into account the asymmetry of the organs of the visual apparatus is impossible and the results may be erroneous.

Help of a loved one

Intercenter distance can be found with the help of a friend or relative. To do this, stand 20 cm apart. The person who conducts the check must sit down so that the second looks above his head at a distant object. Then you need to take a ruler and repeat the same steps as opposite the mirror. But such data may be incorrect, therefore it is recommended to consult an ophthalmologist to correctly measure the interpupillary distance.


Judging by the fact that you are reading these lines now, a victory in the fight against blurred vision is not yet on your side.

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