Pupil Position - PD

Correct eye point position is of utmost importance in progressive lenses fitting.

PD measurement - what can go wrong.

Due to various reasons wearers head position can be in wrong positions, these incorrect lateral head position can lead to substantial PD measurement errors. The diagrams below are clear illustrations of these.

• Diagram on your left indicate the normal and correct position.
• Diagram in the middle indicate the user's head panned to his left, this will result in induced monocular PD values, which may be not required.
• Diagram on your right indicate the user moving towards his left, this position also suggested unwanted monocular PD values. *Possibly to the right too.

I will conclude with basic guidelines to follow when performing PD measurement:

• Assure that the patient's nose and yours are in line and aligned perpendicularly to your face plane.
• Assure that your's and the patient's face plane are the same.
• Record monocular PD values.
• Last but not least, correct use of a PD measurement tool, popularly known as "Pupillometer" can help eliminate unnecessary errors, and possibly quicken the PD measuring process.