A Progressive That Slides: Fit Problem or Design Problem?
A 71-year-old first-time progressive wearer collects a metal frame with adjustable nose pads and skull temples. His Rx is +1.50 −0.50 × 180 with a +2.25 add; fitting height was set at 22 mm with the frame properly fitted in the office. Two weeks later he returns: the frame now sits about 6 mm lower on his nose, distance vision is 'acceptable' but reading is 'below the lens,' and he feels unsteady on stairs. Measured on the face: vertex distance 21 mm (13 mm at dispense), pantoscopic tilt 2°, and the nose pads are splayed so they rest on the lower half of the nose. There is no diplopia, no scratching, and the optical centres sit correctly over the pupils when the frame is pushed back up.
1. Before blaming the progressive design, what do the on-face measurements tell you? Could the vertex change alone explain the symptom?
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The frame is no longer in the position it was fitted in. It has dropped 6 mm, the pads are splayed, and the tilt has collapsed to 2° (typical target 8–12°). When the frame slides down, the fitting cross ends up 6 mm below the pupil, so the entire corridor sits lower relative to the eye than designed. The distance zone is large and still covers the pupil, which is why distance is 'acceptable'; the near zone is now further down, requiring excessive gaze depression or a chin-up posture, and the altered zone geometry at the periphery explains the stairs.
Vertex is not the culprit - check the arithmetic:
- +1.50 / (1 − 0.013 × 1.50) = +1.530 D at 13 mm
- +1.50 / (1 − 0.021 × 1.50) = +1.549 D at 21 mm
That is about +0.02 D - optically irrelevant. The panto change alters the effective sphere/cylinder by a similarly trivial amount. The problem is positional, not refractive.
2. Give your adjustment plan, in the order you would perform it, and state the criterion for deciding to remake.
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- Stabilise the bridge first. Bring the pads in to reduce the splay and set them so they rest on the upper nasal slope; a frame that grips cannot be judged for height.
- Set the temples. Correct the bend point and the skull curve so the frame hooks behind the ears without pressing; if the temples are too long for him, that alone will let the frame creep down.
- Set pantoscopic tilt to 8–10°, then re-check that the back surface still clears the lashes and the cheek.
- Re-measure the fitting height on the face with the frame now stable. If the pupil is back at the 22 mm fitting cross, no lens change is needed.
- Re-check vision with the frame held in the corrected position before adjusting. If acuity and reading are restored, the lenses are exonerated. If the reading zone is still short even with the frame in the correct position, the corridor is truncated by the frame depth → remake with a correctly measured height or a shorter corridor.
- Book a short review in a week - a first-time wearer who has spent two weeks adapting to a wrong position will not feel right immediately.
3. The patient wants to abandon progressives and go back to single vision. How do you respond, and what would change your mind?
Read the worked answer
Do not change the lens design to compensate for a fitting error - that fixes the wrong variable and costs a pair of lenses.
What to say: 'The lenses were made for a frame sitting in a specific place on your face. The frame has slipped, so you have been looking through the wrong part of the lens for two weeks. Let me put the frame back where it belongs and re-check before we talk about changing the lenses.' Then demonstrate: have him hold his head in the corrected posture and read.
What would change my mind:
- The frame cannot be stabilised (bridge too wide for his nose, heavy front, very slippery finish) - then the frame is wrong, not the design, and a frame change is the answer.
- After a correct fit and a fair adaptation period (2–3 weeks), he still cannot tolerate the peripheral swim or the corridor. Then a shorter corridor, a different design, or a single-vision pair with a separate reading pair is a reasonable, patient-centred decision.
Document the fit measurements at each visit; if it ends in a remake, the record should show that the design was not the cause.