"PD Measurement" solution provides both measurements: binocular measurement, and, for those who wear glasses during the protocol, also monocular measurement.
Single or Binocular PD
The “Binocular PD” value represents the distance between the pupils. This term is also call “Single PD” or just “PD”.
The units is commonly millimeters.
This value is used for the mounting of your lenses on the frame in order to place the center of the lens in front of the center of your pupil.
Single PD measure is commonly used for non-high corrections of unifocal eyeglasses.
Dual or Monocular PD
"Monocular PD", or "Dual PD" represents the same distance than single PD but split by the nose in two values.
This is a two-number value showing the distance from the bridge of your nose to your pupil on each side.
In this example, PD Right is 32 mm and left PD is 30 mm.
It means also single PD value is 62 mm.
The dual Pd is commonly used for high correction of unifocals eyeglasses and is a mandatory parameter in progressive or multifocals eyeglasses.
So, is it better to have a single or dual PD number when purchasing your new glasses ?
Our eyes are not equally proportioned or symmetrical. One pupil could be a little further away from the bridge of your nose than the other pupil. Because of this, a dual PD allow you to have a perfect fit.
However, professional are agree to say in some low-middle correction range, using single PD have no impact in for the glasses wearer confort.
Is one more accurate than the other?
Fittingbox solution provide same accuracy in both value for an user respecting the guidelines.
Dual PD : Bias can be introduced with fold frame or asymmetrical frame. Fittingbox can not be resonsible for those cases of non regular use.