Interpupillary distance (PD) is a measurement of the distance between the centres of your two eyes. It is dependent on whether you are buying eyewear for distance or close up. This measurement is used to properly align the centre of your eyeglass lenses with the centre of your eyes.

 If the centers of your eyeglass lenses are not aligned properly, then you may experience:

•         eyestrain
•         headaches
•         distorted vision
•         double vision
•         blurred vision
•         an inability to wear your eyeglasses

A PD measurement is part of the dispensing service, not part of the eye examination. Other dispensing services include:

•         selection of an appropriate frame
•         recommendation of an appropriate lens type
•         thickness and coatings
•         adjustment of the frame
•         proper placement of the bifocal or progressive

 It is the responsibility of the person or company providing the dispensing service to accurately measure your PD.

Multifocal lenses

A multifocal lens is a lens that contains two or more prescriptions for correcting vision at different distances.

There are a number of measurements that your doctor of optometry will take when fitting you for multifocal lenses. As with all multifocal lenses, the two key measurements are the interpupillary distance and the segment height. Both of these determine where the multifocal lens will be orientated in the frame to give you proper vision. Each lens manufacturer has its own version of customized progressives.