Pupillary distance is the distance between the centers of the pupils of the eyes, which is important for properly fitting eyeglasses. It can be measured by eye care professionals or at home with a ruler. Optometrists may exclude pupil distance measurements from prescriptions to encourage patients to order glasses through their office. Incorrectly fitted glasses can cause discomfort and vision problems.
Pupillary distance is the distance between the centers of the pupils of the eyes. This value is typically expressed in millimeters because they are a precise system of measurement useful for very small measurements. Pupillary distance becomes particularly relevant to prescribing eyeglasses, when it is used to ensure that eyeglasses are properly fitted to the wearer’s face. Sometimes it is written directly on the prescriptions and in other cases it may be omitted, for reasons which will be explained shortly.
Optometrists and other eye care professionals can measure pupillary distance using a device customized for the activity. Commonly, two measurements are taken, one while the patient is focusing on medium- and long-range targets and the other while the patient is looking at a close-up target. The pupillary distance will be given in two values, one for distance vision and one for reading vision. This is done for bifocals or prescription reading glasses.
It is also possible to measure the pupillary distance at home with the help of a ruler. It’s usually helpful to have a friend or partner take the actual measurement, although people can be reasonably accurate when looking in a mirror and using a ruler. Pupillary distance can vary widely from person to person, and it’s wise to take at least two measurements to confirm that the measurement is indeed correct, rather than assuming it probably is on the first try.
Some optometrists exclude pupil distance measurements from prescriptions unless specifically asked to add them. This can be a result of forgetfulness, but is more commonly done to encourage patients to order eyeglasses through the optician. Selling lenses and frames can be a big part of the business, and asking patients to order through the office also gives the doctor the ability to check on patients, do a fitting to confirm the glasses fit, and to remind patients when it is time to have another eye exam.
Patients can ask for the PPD measurement to be recorded so they can take the prescription elsewhere. It is sometimes written as a single number and sometimes it is written as two. When two numbers such as 33/27 are shown, it reflects a measurement from the center of each pupil to the bridge of the nose. Some people are surprised to learn that asymmetry isn’t that uncommon when it comes to pupillary distance.
The wrong size glasses are not comfortable to wear and can cause vision problems. At the very least the patient may find that the vision is not corrected properly and the patients may also develop headaches and eye strain because their eyes have difficulty focusing through the lenses. Therefore, it is important to ensure that pupillary distance is considered when wearing glasses.
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