With the increasing popularity of buying eyeglasses online from trusted retailers like Five Season Optical, entering the correct measurements has become essential for a successful fit. The most important measurement of all is the pupillary distance (PD), a seemingly simple number that can mean the difference between comfortable vision and successful glasses, or headaches and persistent eye strain.

In this comprehensive guide, we explain what this measurement means, why it is the most dangerous when buying glasses online, how you can measure it accurately, and when it is preferable to rely on a professional eye exam.

What is the distance between the pupils?

The interpupillary distance is the distance between the center of the pupil of the right eye and the center of the pupil of the left eye, and it is measured in millimeters. This measurement determines the position of the lens in front of the eye, which directly affects visual acuity and visual balance between the two eyes.

Important note: Even if the lens power is 100% correct, an incorrect PD measurement may make the glasses completely uncomfortable.

Why is the distance between the pupils the most important number when buying glasses online?

When buying glasses from a physical store, the specialist will accurately measure this number. However, when buying online, you are responsible for entering it yourself when selecting your eyeglasses .

Any mistake, even just 1 or 2, could lead to:

Frequent headaches
Dizziness and imbalance
blurred vision
Difficulty adapting to the new glasses

Many cases of glasses being returned online are not due to the lenses, but rather to an inaccurate measurement of the distance between the pupils.

When does the PD measurement problem become more apparent?

The problem is most apparent in the following cases:

Using a computer and phone for extended periods
Long-distance driving
Choosing high-resolution lenses
Working in front of screens daily

If your screen usage is intensive, you may need stress-reducing solutions such as Blue Light Screen Glasses.

Does the measurement of the distance between the pupils differ depending on the type of glasses?

In some cases, yes: reading glasses require higher precision for near vision, and some people have a slight difference in vision between their right and left eyes. However, in most online purchases, the general PD measurement is used when choosing frames and lenses.

To understand the effect of lens type on visual clarity and your daily experience: Learn about the types of medical lenses .

How do you measure the distance between your pupils at home?

Method 1: Mirror + Ruler

Stand in front of a mirror at eye level.
Place the zero at the center of the pupil of the right eye.
Read the number at the center of the left pupil.
Repeat the measurement more than once to be sure.

The second method: with the help of another person (more accurately)

Sit up straight.
Look straight ahead.
The other person measures directly between the pupils.

The third method: a clear image + a measuring tool

Take a straight, front-facing photo of your face.
Use a reliable measurement app/tool.

Warning: It is never advisable to guess or rely on the measurements of old glasses without being sure.

Does measuring the distance between the pupils affect the choice of frame?

Yes, directly. A correct PD measurement helps in choosing a frame that suits the face shape, prevents glasses from slipping, and improves weight distribution on the nose.

To choose the most suitable frame: Eyeglass frame shapes that suit the face and check out our guide: How to choose the right eyeglass frame .

You may also need to browse customized options such as men's eyeglasses to choose the best size and design for your face and daily use.

When is it preferable not to take risks and to rely on an eye exam?

A professional eye exam is recommended in the following cases:

When buying your first pair of eyeglasses
When changing the type of lenses
In case of headaches or persistent fatigue
If vision is blurry despite wearing new glasses

You can visit your nearest Five Seasons branch for a more accurate measurement and direct assistance in choosing frames and lenses.

Summary

Interpupillary distance (PD) is not a minor measurement ; it's a key factor in the success of your online eyeglasses purchase. Accurate PD measurement ensures clear vision, long-lasting comfort, and reduces headaches and eye strain. Whether you choose to buy online or visit a Five Seasons store, paying attention to this simple measurement makes a real difference to your daily experience.

Frequently Asked Questions (FAQs)

How do I determine pupillary distance?

You can determine pupillary distance (PD/IPD) in three ways: measuring with a ruler in front of a mirror, with the help of another person (which is the most accurate), or using a clear frontal photograph with a reliable measuring instrument. It's always best to repeat the measurement more than once to be sure.

What is the interpupillary distance (IPD) in an eye exam?

It is the distance in millimeters between the center of the right pupil and the center of the left pupil. In eye exams, it is used to adjust the position of the lenses in front of the eyes so that vision passes through the correct visual center, thus reducing headaches and eye strain.

What is the distance for measuring vision?

The distance for an eye exam varies depending on the type of test, but usually the distance is checked at a distance of about 6 meters (20 feet) or the equivalent using mirrors in some clinics, while the reading exam is at a close distance (usually 35–40 cm).

How do you read the results of an eye exam?

An eye exam result (glasses prescription) typically includes: SPH for nearsightedness/farsightedness, CYL and AXIS for astigmatism, ADD for reading lenses (especially after age 40), and sometimes PD/IPD for lens alignment. Even a slight change in these values can affect visual clarity and comfort.

What does 1.25 mean in terms of perspective?

The number 1.25 may appear in two ways depending on the context of the prescription: if it is written with a plus (+) or minus (-) sign next to SPH , it indicates the degree of correction for myopia/hyperopia. If it is within ADD , it is an additional reading supplement (common after age 40). The precise interpretation depends on the number's position within the prescription and its function.

What is the shape of the pupil?

The pupil is the black opening in the center of the eye (within the iris), and its shape is usually round. Its size changes (dilates/constricts) depending on the intensity of light and the state of the nervous system, which is normal.

What is the difference between sph and cyl?

SPH determines the degree of myopia or hyperopia (the basic power of the lens), while CYL determines the degree of astigmatism/astigmatism (irregularity of the curvature of the cornea), and is often accompanied by AXIS which determines the direction of this correction.

How do I measure IPD?

To measure IPD, place a straight ruler in front of your eyes. Place the zero at the center of your right pupil and read the number at the center of your left pupil. For greater accuracy, have someone else measure it for you and repeat the process 2–3 times, then take the average.

What are the highest degrees of myopia?

There is no fixed "maximum" limit for everyone, but medically, high myopia is usually considered when the SPH value is approximately -6.00 or higher (e.g., -7.00, -10.00). The higher the degree, the more close monitoring the eye will require by an ophthalmologist.

What is normal visual acuity?

Normal visual acuity is often measured as 6/6 (or 20/20) on the Snellen scale, meaning that a person can see at a distance of 6 meters what a person with normal vision can see at the same distance. Figures may vary depending on the measurement method and the country.

What does CYL mean in vision measurement?

CYL is the amount of astigmatism correction. If this value is present in the prescription, it means the eye needs additional correction due to an irregular curvature of the cornea or lens. It is often accompanied by AXIS to indicate the direction.

What is the normal range of vision?

Normal vision is often defined as close to 6/6 (20/20). However, what constitutes "normal" varies depending on age and eye condition, and slightly lower vision may be possible without any underlying medical issue. A comprehensive eye exam is the best way to determine this.

What is the interpupillary distance (IPD)?

It is the distance between the centers of the pupils in millimeters. It is used to adjust the position of the lenses within the frame so that the optical point in the lens is aligned with the eye, which improves comfort and reduces headaches and blurred vision, especially when buying glasses online.

What is the best measurement for vision?

The best "measurement" is the most accurate assessment of your actual condition, achieved through a comprehensive eye exam that includes refraction measurement (SPH/CYL/AXIS), evaluation of the eye's surface, and assessment of your daily needs (screens, driving, reading). There is no single "best" number for everyone; the best is what works best for you.

What is the scale for measuring degrees of visual impairment?

It often refers to classifying the severity of visual impairment into degrees. Generally speaking:

Mild myopia: up to approximately -3.00
Moderate myopia: approximately -3.00 to -6.00
High myopia: -6.00 or more

A similar classification applies to farsightedness with positive values. The precise determination depends on the doctor's measurements and the condition of the retina and cornea.

Interpupillary distance (PD) is the most important measurement for buying your glasses online – Five Seasons