03/08/2026
Bifocal and progressive Lens Measurement.
For bifocals, the key is placing the reading segment at the right height.
What is measured:
Monocular PD (Pupillary Distance): Distance from each pupil to the nose center
Segment Height (Seg Height): From the bottom of the frame up to a reference point (usually the lower eyelid or pupil, depending on lens type)
How it’s done:
The patient wears the chosen frame
The optician marks where the near portion should start
Measurements are taken while the patient looks straight ahead
Why it matters:
If the segment is too high → annoying for distance vision
If too low → you’ll struggle to read comfortably
Progressive Lens Measurement
Progressives are more advanced, so the measurements are more detailed.
What is measured:
Monocular PD (very precise)
Fitting Height: From frame bottom to the center of the pupil
Vertex Distance: Space between eye and lens
Pantoscopic Tilt: Angle of the frame on the face
Frame Wrap Angle: How the frame curves around the face
How it’s done:
The patient wears the frame in a natural position
The optician aligns the fitting cross directly with the pupil
Sometimes digital tools are used for higher accuracy
Why it matters:
Progressives have multiple zones (distance → intermediate → near).
Even a small error can cause:
Blurry vision
Difficulty adapting
Eye strain
Quick Comparison
Bifocal: Simpler, fewer measurements
Progressive: More precise, customized fitting.