Open Dome, Feedback, and a Patient Who Refuses a Custom Mold
A 72-year-old woman with a mild sloping to severe high-frequency loss is fitted bilaterally with open domes. She has worn the devices for two weeks and reports whistling when she hugs her grandchildren and when she puts on a hat. She also reports that the devices 'slide out' when she chews and that she hears her own voice as hollow. Her audiogram shows thresholds of 30 dB HL at 500 Hz and 75 dB HL at 4000 Hz. She tried a custom mold years ago with a previous device and found it 'unbearable' and 'plugged up.' She is adamant she will not return to a mold.
1. Separate the feedback, migration, and occlusion complaints and explain what is driving each.
Read the worked answer
These are three distinct problems with different causes and different fixes.
Feedback: with an open dome and 75 dB HL at 4 kHz, the prescribed high-frequency gain is high, and the open vent path allows amplified sound to leak back to the microphone. Hugging and hats bring reflective surfaces near the microphone, which is why it appears in those situations rather than constantly.
Migration: a dome that does not match her canal anatomy will back out during jaw movement. Chewing changes canal shape, and an under-sized or incorrectly angled dome will not maintain seal or position.
Occlusion: her hollow voice is the low-frequency energy trapped in the occluded portion of the canal. Paradoxically, she is reporting occlusion with an open dome, which suggests the dome is seating deeply enough in a narrow canal to trap some low-frequency energy, or that the receiver is positioned where it partially blocks the canal.
Each complaint must be addressed on its own terms; a single gain reduction would not solve all three.
2. She refuses a custom mold. What options do you have, and how would you evaluate success?
Read the worked answer
Options short of a full custom mold: (1) a different dome style, including a vented or tulip dome or a dome sized to her canal, which can improve retention and reduce feedback while preserving venting; (2) a custom slim tube or a receiver with a custom tip, which offers more seal than a dome with less occlusion than a full shell; (3) repositioning the receiver depth, since a deeper placement can reduce the occluded volume and the hollow-voice sensation; (4) modest high-frequency gain reduction paired with feedback management, accepting a small target deviation to preserve comfort.
Evaluate success with real-ear measurement in the aided condition, a feedback test or probe with the hat and hug maneuvers reproduced, and a direct report of her own-voice quality. Ask her to rate the hollow voice on a simple scale before and after. If feedback persists at target gain with the best non-custom option, revisit the mold conversation using a small vent and soft material, framed as a different experience from the one she remembers, rather than as a repeat of it.