8.4 Multifocal and PAL Troubleshooting

Start with verification, not assumptions

Multifocal complaints can sound similar even when the causes are different. I cannot read may mean the segment is too low, the add is wrong, the frame is sliding, the working distance is unusual, the patient is using the wrong zone, or the lenses were made incorrectly. I feel swim may mean progressive adaptation, excessive wrap, wrong base curve, wrong fitting height, or prescription change.

The first step is to verify. Use a lensmeter and layout markings when available. Confirm sphere, cylinder, axis, add, prism, lens design, monocular PDs, segment heights or fitting-cross heights, and frame adjustment. Compare the finished eyewear with the order and with the patient's actual wearing position.

Basic troubleshooting workflow

A patient script is: I want to separate three possibilities: whether the lenses were made as ordered, whether they are sitting in the measured position, and whether this design matches the task you are trying to do. We will check those before deciding on a remake.

Lined bifocal and trifocal complaints

Lined multifocals provide clear zones but also visible borders and abrupt power changes. A flat-top bifocal that is too low makes the patient lift the chin to read. A segment that is too high may interfere with walking, stairs, or distance viewing. A trifocal may help intermediate vision, but only if the intermediate distance matches the task.

For a bifocal patient who works at a computer, do not assume the near add is wrong. A standard bifocal near segment is usually optimized for closer reading than a desktop monitor. The correct discussion may involve a trifocal, occupational lens, computer single vision, or a separate pair.

PAL complaints

Progressive addition lenses provide distance, intermediate, and near power without a visible line, but the usable zones are design-dependent. They also contain peripheral blur and require correct fitting. New wearers need instruction on pointing the nose toward tasks and using head movement for side viewing.

Common PAL complaints include distance blur, narrow reading, swim, difficulty with stairs, poor computer vision, and needing to tilt the head. Each symptom has multiple possible causes.

Markings and reference points

PALs have temporary ink markings and permanent engravings. The fitting cross, prism reference point, distance reference point, and near reference point allow verification. If markings are missing, the optician may need to locate permanent engravings and re-mark the lenses using the manufacturer's layout chart. On the NOCE, the key idea is that troubleshooting a PAL requires reference marks; guessing from the visible lens shape is not enough.

For lined multifocals, measure segment height from the deepest point of the eyewire or lens shape to the top of the segment. Confirm the frame is level and in wearing position. Unequal patient anatomy may justify unequal heights, but accidental unequal heights can cause symptoms.

Adaptation versus nonadapt

Adaptation is a real process, especially for first-time PAL wearers, large prescription changes, cylinder axis changes, anisometropia, and major design changes. However, adaptation should not be used as a substitute for verification. A patient should not be told to just get used to lenses that are made incorrectly, measured wrong, or sitting badly.

Good counseling is specific. Say: The side areas of a progressive are not meant to be as clear as the center channel, so turn your head toward what you want to see. Avoid vague dismissal such as: Everyone hates progressives at first.

Case example

A patient says a new PAL has great distance but the computer is blurry. Verification shows the prescription and fitting height are correct. The patient uses a large monitor at eye level and works eight hours daily. This may be a product-design mismatch, not a remake. An everyday PAL may have limited intermediate width. A computer or office lens could be recommended for that task.

Another patient says the reading area is too low. On inspection, the frame has spread and now sits 4 mm lower than when measured. Adjusting the bridge and temples may restore the fitting cross. If the frame cannot stay in position, a remake alone may fail again because the frame is unstable.

Exam approach

For multifocal troubleshooting questions, follow the sequence: listen, verify, inspect fit, recheck measurements, recreate task, then decide. If a question says the patient cannot see the computer through a bifocal, think working distance and occupational design. If it says a PAL wearer must lift the chin to read, think low fitting height or slipping frame. If it says one eye is worse, think monocular PD, unequal height, frame twist, or lens verification.