What is the pupillary distance (PD)?
Pupillary Distance known as PD, the pupillary distance refers to the distance between the pupil centres in two eyes and it is expressed in millimetre (mm). The measurement is used for locating spectacle lens focal point to ensure accurate vision. And it is necessary data for creating user-defined prescription glasses as well. In general, the PD for most adults ranges from 55 to 75mm and that for children ranges from 42 to 54mm.
What is the Single PD vs Dual PD?
The Single PD or binocular PD refers to the distance from the Centre of the right pupil to that of the left pupil.
The Dual PD or monocular PD refers to the distance from the pupil Centre of the right or left eye to the nasal centreline. It is expressed in 32/30. The left one stands for the measurement for the left eye, the right for the right eye. The monocular PD should be measured if anyone needs to get a pair of progressive multifocal lenses.
How to measure your PD?
Your PD may be specified in your prescription. Please ensure that it is the latest (within 12 months). If the PD is not applicable or available, it is suggested that your friend or family member should help you measure your PD. In addition, a ruler with accuracy of millimetre should be prepared.
Please open your eyes and let your friend place the null point at the Centre of one pupil and measure the distance to the Centre of the other pupil. You should keep your eyes still to the greatest extent without looking at the measurer.
Repeat Step 1 for two times to get an average value
- The PD for male adults is 60 – 75mm and that for female adults is 55 – 68mm.
- If the PD is not an integer (e.g. 58.5), please select 59 if you are short-sighted or select 58 if you are farsighted/presbyopic, for optometrists handle such issues as per the principle of selecting higher values for short-sighted persons and selecting lower values for farsighted people.
The above is about regular measurement of PD by using a simple tool. If you are a patient with cyclopia, strabismus, progressive multifocal lenses, or serious spectacle lens power, it is suggested that you should go to a professional eye hospital and let a doctor examine your eyes with some special instruments.