A First Progressive in a 26 mm Frame on an Asymmetric Face
A 63-year-old retired teacher is ordering her first pair of progressive lenses. She chooses a metal frame with a 50-18 eye size and a 26 mm B measurement because it suits her face. With the frame adjusted on her face, her pupils sit 15 mm above the lower lens edge, her monocular PDs are 30.0/30.5, and the as-worn vertex distance is 13 mm. Her prescription is +1.25 −0.50 × 090 in both eyes with a +2.50 add. She reads paperbacks in bed, works at a desktop monitor about two hours a day, and plays bridge twice a week. The frame arrived with 14° of pantoscopic tilt; because the bridge sits 3 mm low on her nose, the optician has flattened the tilt to 4° to keep her pupils centred, and the temples now rest high on her ears. Her right pupil is 2 mm lower than her left.
1. Evaluate whether a 15 mm fitting height in a 26 mm B frame is workable for this wearer and state what you would order.
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A 15 mm fitting cross in a 26 mm deep lens is at or below the minimum for a conventional progressive corridor and leaves almost no distance zone above the fitting cross and a compressed reading zone below it. With a +2.50 add the near zone is already the most demanding part of the lens, and her reading and card-playing mean she will spend real time in it.
Options:
- Short-corridor design: minimum fitting heights are commonly around 14–15 mm, so a 15 mm fit is technically achievable, but the intermediate is sacrificed to buy that - poor for the desktop work she describes.
- Better: change the frame to a deeper B (30 mm or more), which typically yields 18–20 mm of fitting height and lets a standard corridor deliver usable distance, intermediate, and near zones.
- If she refuses to change frames, consider an occupational/office design for the desk and bridge, and be honest that a 26 mm B with a +2.50 add will produce a small near zone.
Judgement: the frame is the variable to change. Pushing a general-purpose PAL into a shallow frame is the classic first-pair non-adaptation, and it is easier to fix now than to explain a return later.
2. Assess the pantoscopic tilt compromise and describe how you would refit the frame instead.
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Flattening 14° of tilt down to 4° to 'centre the pupils' is treating a symptom of a frame that sits too low. What it costs:
- With reduced tilt, the bottom of the lens swings away from the face, so the reading point is further from the eye and effectively less plus arrives at the eye; the near zone also shifts relative to where the eye actually looks when it converges and depresses.
- A PAL corridor is designed around a nominal as-worn tilt. Removing 10° misplaces the corridor vertically and changes the effective sphere and cylinder at the reading level, which the wearer experiences as a narrow, 'swimmy' near zone.
- The temples resting high on the ears means the frame is being held by the wrong part of the bend and will slide, so the fitting cross will not stay at 15 mm anyway.
Correct sequence: raise the frame at the bridge by adjusting the nose pads and pad arms so the pupils sit at the intended height, then restore 8–12° of pantoscopic tilt by bending at the hinge/endpiece and re-bending the temples so the bend sits on the ear and the frame is level. Measure PD, fitting height, vertex, and tilt as worn, after adjustment, and put those as-worn values on the order.
3. Her right pupil is 2 mm lower than the left. How do you mark and order, and what happens if a single fitting height is used?
Read the worked answer
Mark both eyes independently. With the frame adjusted and level, dot each pupil (or the desired fitting cross position) and record two separate fitting heights - for example 15 mm OD and 17 mm OS - along with separate monocular PDs measured at those points. Modern free-form processing accepts per-eye fitting height; if the chosen design or lab cannot, say so before ordering rather than discovering it at dispense.
If one height is used for both eyes:
- One eye sits off the corridor. The right eye, being lower, would have its fitting cross above the prescribed height, pushing its distance zone up and its near zone lower, so the two eyes are working different parts of the lens at the same gaze - a common cause of 'I can't find the reading area with my right eye.'
- There is a vertical prismatic imbalance at near. At near, the power is about +3.75 D, so 2 mm of vertical misplacement is roughly 0.2 × 3.75 ≈ 0.75Δ per eye of vertical effect, which is enough to cause asthenopia in a first-time wearer even without anisometropia.
- Adaptation is slower and the patient is more likely to blame the design rather than the measurement.
Document the as-worn measurements with a photograph or a marked demo lens and keep them with the order so the remake matches.