Why PD is Important and How to Measure It


What is PD?

If you have purchased a frame of eyeglasses before, chances are that you must have heard about a pupillary distance (PD), also known as the the measurement of the eyes. If you have an experience of purchasing eyeglasses online, then you must have heard about the term, "Pupillary measurement". You must have also measured it yourself before.  Did you know how important it is to know this number before you purchase online? The reality is unless you have an accurate number with you, your glasses won't fit you well. If your glasses won't fit you well, you might have headaches or blurry visions, often causing stress or anxiety.  The pupils are positioned right in the center of your eyes.  They are the black circles positioned in the center of the colored area of your eyes, known as the iris. This is a muscle which dilates (open) or constricts (closes) to allow more or fewer eyes into the eyes. Our pupils tend to dilate at night to allow more light, to help us see well.  Our structure of the eye is such that pupils are in the center, directing the light at the center of the retina. This is just like focusing on the target with a bull's eye in the center. The pictures that a human eye sees focus through the pupil center onto the bull's eye.

There are two types of PDs. One is the binocular PD that is measured between two pupils. The other is known as the Monocular PD, which is measured from the center of a pupil to the center of the nose’s bridge. Nevertheless, The Monocular PD is much accurate as compared to the other one as eyes may not be centered equally. The Monocular PD can thus make up for this imbalance. Binocular PD on the other hand can be used for patients with low prescriptions as this does not lead to eye strains or any other symptom.    

Why PD is Important?

Pupillary distance, which is sometimes called Pupil Distance or PD is the difference between the bridge of the nose and center of each pupil in millimeters.  PD is vital, especially when crafting a prescription glasses. A PD helps to determine where the center of the vision must be placed on a lens.  The prescription of a lens can be taken off-center without a correct measurement. Correct measurement is also important to see out of the glasses, even if the prescription is 100 percent correct.

PD is important. When fitting the glasses on to patients' eyes, the pupils must be well aligned with lenses' optical centers. An accurate PD will make sure that the person does not experience an unwanted prism due to decentration. A person's vision is highly affected if the PD measurement is wrong. This is similar to wearing someone else's glasses.

A poor PD measurement can result in stress, fatigue, blurry visions, and headaches. With the wrong PD and high prescription, symptoms can be worse.  Some patients often complain that they don't feel right. A few times, it may be a vague sense that something is not right with the glasses.

The average measurement of a PD is between 60 mm and 66 mm. It is possible to select the average PD while adding the prescription online. If you think you are falling outside the typical range, you must get an accurate reading for yourself. The ideal way is to measure. If your prescription Is strong, it is essential to measure your PD. The stronger the lens prescription, the more essential it becomes to a lens centration

How to M

easure the PD

A PD is typically measured by an eye doctor as part of an eye exam.  This is done using a corneal reflex pupillometer or a pupillary distance ruler, calibrated particularly to each eye.

Measuring your PD is very simple. If you have your eyeglass prescription and you are looking for a stylish pair of wireframe glasses on the internet, PD measurement can be done in minutes. All you need is a mirror and a millimeter ruler.

The distance between you and the mirror should not be more than 8 inches.  Hold the ruler above the eyes and flat against your eyebrow.

Close your right eye while aligning the zero on the ruler to the center of your left eye. Record your measurement from the rulers' zero to your right pupil. Make sure to keep the eye closed without moving the ruler.

Your PD is the distance. If you are measuring the reading glasses, or if you are farsighted, you must subtract 3mm.

Make sure to repeat these steps a few times to make sure that you have collected the most accurate PD measurement for your new pair of eyeglasses.

However, If you want to buy a second pair of eyeglasses but doubt the PD measurement, you can easily get the measurement from your current eyeglasses with the help of a millimeter ruler and felt-tip marker 

Begin with your glasses on and focus on any object that is 20 feet from where you stand or sit.

As you stare at the object, reach up with a pen or a marker, make a little mark where the object appears in the right eyeglass lens

Do the same on the other side.

After you have marked both points, these should then line up with a single dot in the field of your vision as you focus on the object. If you do, this means you have measured correctly.

Take your glasses off and measure the distance between the two dots with your millimeter ruler. You will finally have your PD measurement, and ease to upgrade to a new pair of frames.

Important tip: Calculating the PD on your own with a millimeter ruler will not be as accurate as the measurement done by an eye doctor. To get an ideal pair that best fits your eye, schedule an eye exam. 




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