All about pupillary distance and its uses

Have you got your eyes examined ever or do you wear eyeglasses? Have you accompanied your parents or spouse to the optical store and noticed how eyes examination is conducted? Then surely, you must have seen the prescription that is handed over by the optometrist/ophthalmologist. Well apart from the negative and positive powers in the prescription, there are certain other terms and terminologies which are written on the prescription. Along with the words such as OD, OS, Axis, Cylinder and Prism, you might have noticed the word PD or Pupillary Distance written on the prescription. It may sound something new to you, but it is actually a very important criteria when it comes to measurements of the eyeglasses frame and crafting the correct prescription glasses.

What is the pupillary distance?

We all know that pupils are the center of the eyes i.e. the black coloured circle in the eyes, called the iris. Pupillary Distance (PD) or interpupillary distance (IPD) is the distance between the centers of the pupils of the eyes that is measured in millimetres and varies from one person to the other.  Pupillary distance is required by the optician at the time of crafting the eyeglasses so that the lenses are positioned accurately. This horizontal distance is measured from the middle of one pupil to another considering the bridge of the nose a the center point.

What is the pupillary distance in glasses?

When the eyeglasses are crafted at the laboratory of the eyewear provider, it becomes absolutely important to have the perfect details of the PD. Thus, with the help of exact digits of the PD measurement, the laboratory experts can create the eyeglasses lens which can help the user to focus on the objects from the right focal point.

What if the pupillary distance is wrong?

The use of the wrong eyeglasses that consists of the wrong PD can cause severe eye health issues. Therefore, wrongly crafted eyeglasses can lead to blurry vision, fatigue, stain, headache and inability to focus clearly on the object.  The user may find it difficult in adjusting with the glasses, especially people who have higher prescription power lenses. Therefore, the accuracy of the PD plays a vital role in making the perfect eyeglasses in conformity with the prescription

What are the types of Pupillary distance?

There are basically two types of PD, they are as mentioned below: 

1- Binocular Pupillary Distance:  In this PD, the distance is measured from the center of one pupil to the other.

2- Monocular Pupillary Distance:  Here, the distance of PD is measured from the center of one pupil to the center of the bridge of the nose. It is a better and accurate technique for measuring PD.

Monocular PD is usually required while creating the progressive lenses and bifocal glasses so that he centers of the glass lenses are accurate and do not deviate from the focal point. Whereas the binocular PD is used for single vision lens having single power in the entire lens and for eyeglasses with lower prescription powers.

How is the pupillary distance measured?

There are certain simple ways for measuring pupillary distance and the best method is to get it measured by visiting an Optometrist. With the help of a device known as ‘’Pupillomter’’, the Optometrist gets the exact pupillary distance for creating eyeglasses.

The other way is to measure using a ruler. Sit in front of the mirror, take any regular ruler having millimetre measurements. Now keep the ruler starting from 1-millimetre measurement point on the center of the pupil of one eye. Track and mark the point where you notice the center of the pupil of the other eye. Note down the distance/ measurement which is your PD. You can also do this with the help of your friends, who can measure PD for you, in case you find it difficult.

What is the right pupillary distance?

Generally, the average adults have PD that measures between 54mm to 74 mm. Regarding kids, it can be anywhere between 43mm to 58 mm.

Is pupillary distance important for reading glasses?

Correct PD is absolutely necessary for prescription glasses including reading glasses. Since the purpose of measuring PD is to find out the focal point on the eyeglasses lens. Thus, the accurately measured PD helps in depicting the exact focal point from where the light rays can pass and help eyes in focusing objects so that they appear clear and not blurry. In fact, not only reading glasses, PD is essential for distance, varifocals as well as bifocal glasses too.