How do you measure progressive fitting height?

With the properly adjusted frame on the patient, face them at the same eye level. Have the patient look straight ahead at a distant target in natural head position. Mark the center of the pupil on the demo lens with a marking pen. Remove the frame and measure from the lowest point of the lens opening to the mark. This distance in millimeters is the fitting height.

What is the minimum fitting height for progressive lenses?

It depends on the specific progressive design. Standard corridor progressives (14-18 mm corridor) need approximately 22-24 mm minimum fitting height. Short corridor designs (11-14 mm) can work with 18-20 mm. Ultra-short corridor designs may work as low as 16-17 mm. Always check the lens manufacturer's specifications for the chosen design.

What is the difference between seg height and fitting height?

Seg height (for bifocals) measures from the bottom of the lens to the top of the visible segment line, typically positioned at the lower lid margin. Fitting height (for progressives) measures from the bottom of the lens to the center of the pupil, where the invisible fitting cross is placed. Fitting height is almost always a higher number than seg height in the same frame.

What happens if progressive fitting height is wrong?

If too high, the patient looks through the intermediate or near zone for distance vision, causing blurry distance and the urge to tilt the head back. If too low, the patient cannot access the full near zone and struggles to read. Either error typically requires remaking the lenses with the correct fitting height. Even a 2 mm error can cause noticeable visual problems.

Progressive Fitting Height: Precise Vertical Positioning for PAL Fitting

What Is Progressive Fitting Height?

Progressive fitting height is the vertical distance from the lowest point of the lens opening in the frame to the center of the patient's pupil (the fitting cross position). Unlike bifocal seg height, which positions a visible line, progressive fitting height positions an invisible reference point that determines how the entire progressive corridor aligns with the patient's visual axis.

Why Fitting Height Is Critical for Progressives

Progressive lenses have a fixed corridor design with specific zones for distance, intermediate, and near vision. The fitting cross must align with the patient's pupil center so that:

The distance zone is above the pupil when looking straight ahead
The intermediate corridor is accessible with a slight downward gaze
The near zone is reached with a comfortable reading gaze (typically 25-35 degrees below straight ahead)

If the fitting height is wrong, the entire progressive corridor is displaced vertically, forcing the patient to adopt unnatural head positions to access the correct zone.

How to Measure Fitting Height

Adjust the frame: Ensure the frame is properly adjusted and sitting correctly on the patient's face
Natural head position: Have the patient assume their natural head position, looking straight ahead at a distant target
Mark the pupil center: While facing the patient at the same height, use a marking pen to place a dot or horizontal line on the demo lens at the center of the patient's pupil
Remove and measure: Take the frame off and measure the vertical distance from the lowest point of the lens opening to the pupil mark
Record in millimeters: This is the fitting height for the progressive lens order

For the most accurate fitting height, use a digital centration system if available. These systems photograph the patient wearing the frame and use software to precisely locate the pupil center relative to the frame edges, eliminating the parallax and marking errors of manual measurement.

Fitting Height vs. Seg Height

Measurement	Progressive Lenses	Bifocal Lenses
What is positioned	Fitting cross (invisible)	Segment line (visible)
Reference point	Center of pupil	Lower lid margin
Typical height	Higher (varies, typically 16-22 mm)	Lower (varies, typically 14-18 mm)
Precision needed	Very high (1-2 mm matters)	Moderate (2-3 mm range acceptable)

Progressive fitting height is measured to the pupil center, while bifocal seg height is measured to the lower lid margin. Progressive fitting height is almost always higher than bifocal seg height in the same frame because the pupil center is higher than the lower lid margin.

Minimum Fitting Height by Design

Different progressive lens designs have different minimum fitting height requirements. The frame's B dimension must be deep enough to accommodate the full progressive corridor:

Standard corridor (14-18 mm): Requires approximately 22-24 mm minimum fitting height
Short corridor (11-14 mm): Can work in frames with 18-20 mm minimum fitting height
Ultra-short corridor (less than 11 mm): Designed for frames with 16-17 mm minimum fitting height

If the fitting height is too low for the chosen progressive design, the patient may not be able to access the full near zone. Always check the specific lens design's requirements before confirming the frame and fitting height.

Common Errors

Fitting Height Too High

Patient looks through the intermediate or near zone for distance vision
Distance vision is blurry
Patient tilts head back to clear the distance zone

Fitting Height Too Low

Patient cannot reach the full near zone even when looking down
Reading is difficult or impossible
The near zone is cut off by the bottom of the frame

Using bifocal seg height guidelines for progressive fitting. Progressive fitting height is higher than bifocal seg height because it references the pupil center rather than the lower lid margin. Applying bifocal rules to progressives results in a fitting cross that is too low, causing the patient to look through the intermediate zone for distance vision.

Monocular Fitting Heights

Just as monocular PD is more accurate than binocular PD, monocular fitting heights (separate measurements for each eye) account for vertical facial asymmetry. If one eye sits higher in the frame than the other, separate fitting heights ensure each eye's progressive corridor is properly aligned.

Clinical Relevance

Progressive fitting height is one of the most critical measurements in progressive lens dispensing. A 2 mm error is immediately noticeable to the patient and typically requires a remake. Investing the time to measure accurately during dispensing prevents costly remakes and ensures the patient adapts to their progressive lenses quickly and comfortably.

Key Takeaways

Progressive fitting height is measured from the bottom of the lens opening to the pupil center
It determines the vertical position of the entire progressive corridor
Fitting height for progressives is higher than seg height for bifocals
Check the specific progressive design's minimum fitting height before confirming the frame
A 2 mm fitting height error is noticeable and usually requires a remake
Digital centration systems provide the most accurate fitting height measurements