1 Department of Computer Science, Faculty of Science, Københavns Universitet2 The Image Section, Department of Computer Science, Faculty of Science, Københavns Universitet3 Oticon4 Department of Computer Science, Faculty of Science, Københavns Universitet
The popularity of hearing instruments deeply placed in the ear canal has been driven by their superior cosmetic characteristics. However, people fitted with these hear- ing instruments often complain about the sound qual- ity of their voice, which is typically described as being hollow, echoing, or like talking in a barrel. This problem is caused by the occlusion effect. The effect is primarily due to vibrations of the walls in the soft part of the ear canal, which generate a sound pressure that is trapped in the cavity between the tip of the occluding hearing aid and the tympanic membrane. If the hearing aid is fitted with a seal in the bony portion of the ear canal, preventing vibration in the soft part of the ear canal from reaching the tympanic membrane, then occlusion problems can be solved or at least reduced in most cases. 1–4 Work carried out by Garcia has shown that if the seal of the hearing aid in the bony portion of the ear canal is broken, the occlusion effect increases and often results in perceived occlusion problems. 2 In line with this finding, it becomes very important to make sure that a deeply fitted hearing instrument in fact has a bony seal. This means that the hearing-aid fitter must be able to identify the bony portion of the ear canal to ensure that the hearing aid has the ability to seal in this portion of the ear canal. As part of our clinical activities, we have frequently performed analyses of ear impressions on a case-by-case basis and wondered if more information on identifica- tion and geometry of the bony portion was available. A detailed review of the literature on ear canal anatomy lacked thorough information, which inspired us to undertake a project to provide more insight on this issue. Data from this project provide important new insights about working with deeply-fitted hearing instruments.