Frame Selection for Progressives
Frame selection is the first critical decision in progressive lens dispensing. The frame must provide enough vertical depth to accommodate all three viewing zones: distance at the top, intermediate in the middle, and near at the bottom.
The minimum recommended B measurement (vertical depth of the lens opening) varies by progressive design, but generally:
- Standard corridor progressives: 28-30mm minimum B measurement
- Short corridor progressives: 22-26mm minimum B measurement
- Occupational/office progressives: Design-specific, consult the manufacturer
A frame that is too shallow cuts off the near zone, forcing the patient to tilt their head excessively to read. Conversely, an extremely tall frame can make the distance-to-near transition uncomfortably long.
Marking the Fitting Cross
The fitting cross (or fitting point) determines where the progressive design is centered on the lens. It must align precisely with the patient's pupil center during primary gaze (looking straight ahead at a distant target).
To mark the fitting cross accurately:
- Adjust the frame so it sits properly on the patient's face with correct pantoscopic tilt, vertex distance, and face form
- Sit directly in front of the patient at the same height
- Have the patient look at your eyes (or a distant target behind you)
- Mark the pupil center on both lenses using a marking pen or digital measurement device
- Measure the height from the bottom of the lens groove to the mark
The fitting cross position determines the fitting height, which you report to the lab. Even 1mm of error can shift the reading zone or misalign the distance zone.
Understanding Corridor Width and Length
The progressive corridor is the channel of clear vision that transitions from the distance zone at the top to the near zone at the bottom. Its width and length directly affect the patient's visual experience:
Corridor Length
- Standard corridors (14-18mm): Gradual power change, wider intermediate zone, requires taller frames
- Short corridors (10-13mm): Faster power change, fits smaller frames, but narrower intermediate zone with more peripheral distortion
Corridor Width
- Wider corridors: Larger area of clear vision at each distance, less head turning needed, but more peripheral distortion at the edges
- Narrower corridors: Smaller clear zone, more head turning required, but potentially less overall distortion in some designs
Modern digitally surfaced (free-form) progressives allow designers to optimize the corridor for each patient's specific prescription, frame, and wearing position.
Patient Education and Adaptation
Successful progressive lens wear depends heavily on patient education. Before dispensing, explain:
How to Use Progressive Lenses
- Distance viewing: Look straight ahead through the upper portion of the lens
- Intermediate viewing (computer, dashboard): Lower your chin slightly to use the middle zone
- Near viewing (reading, phone): Drop your chin and look through the lower portion
- Point your nose: Turn your head to face what you want to see rather than just moving your eyes to the sides, which moves into the distorted peripheral areas
What to Expect
- Peripheral blur on both sides of the lens is normal and inherent to progressive design
- Slight swim or sway sensation during head movements for the first few days
- Stairs may feel different initially since looking down engages the near zone
- Full adaptation typically takes 1-2 weeks of consistent full-time wear
Verification of Progressive Lenses
Progressive lenses have manufacturer-specific verification engravings laser-etched onto the front surface. These typically include:
- Two small circles or logos indicating the distance reference points
- A near reference point marking
- Add power identifier
- Design name or code
Use these engravings to verify that the fitting cross aligns with the pupil, the corridor is centered, and the add power is correct. The engravings are invisible during normal wear but visible under specific lighting angles or with a verification stamp.
Common Progressive Dispensing Issues
| Issue | Possible Cause | Solution |
|---|---|---|
| Cannot find reading zone | Fitting height too low, frame sitting too low | Raise fitting height, adjust nose pads |
| Distance vision unclear | Fitting height too high, excessive tilt | Lower fitting height, adjust tilt |
| Narrow usable zone | Short corridor in small frame, high add power | Consider longer corridor design, taller frame |
| Excessive swim | High cylinder, large Rx change, frame fit | Optimize frame fit, allow adaptation time |
| Computer vision poor | Intermediate zone too narrow or at wrong height | Consider occupational progressive or adjust fitting |
Key Takeaways
- Select frames with sufficient vertical depth for the progressive design being used
- Mark the fitting cross at the pupil center during primary gaze with the frame properly adjusted
- Standard corridors suit taller frames; short corridors are needed for smaller frames
- Patient education before dispensing is essential for successful adaptation
- Use manufacturer verification engravings to confirm fitting cross position and add power
- Most progressive complaints can be resolved by addressing frame fit or providing adaptation guidance