Besides an obvious cosmetic advantage, deeply seated “invisible in the canal” (IIC) hearing devices have many acoustic advantages as well, such as greater gain, less occlusion, and ability to take advantage of directional cues naturally. But by default, IIC fittings require a deep impression not just past the second bend of the ear canal (where ideally every impression should reach for sound path information), but for some manufacturers, well beyond it up to an ear dam placed against the tympanic membrane itself. Despite the cosmetic and acoustic advantages of IIC devices, not all audiologists are comfortable taking very deep impression due to the potential risks involved; as audiology graduate students, we’re told many a cautionary tale about the danger of ear impression taking in general, including horror stories of impressions that became attached to the eardrum or caused perforation.
In the July-August 2013 issue of Audiology Today, Leavitt and colleagues review the methodology and literature of deep impression techniques, discuss their group’s experience taking deep impressions on six individuals using various types of ear dams, as well as present a case study of a “worst case scenario” of an impression that got stuck in one author’s ear. In summary, of the 30 deep impressions the group had taken, three (10%) got stuck in the canal. In the case described in depth, even slight motion of the impression caused the patient considerable pain. She was turned away from the first emergency room she visited. The impression was finally removed by an otolaryngologist (also an author on the resulting article) with the aid of mineral oil injected down the hollow, vented ear dam. While the adherence of the impression created a visible lesion on the tympanic membrane, the patient-author recovered fully and was able to wear her IIC device. (This individual has a profound hearing loss in the opposite ear, so any decrease in hearing in the better ear could have been devastating.)
The authors offer both cautions and guidelines to deep impression taking. In their experience, trimmed down, small foam rubber ear dams are less likely to cause adherence than cotton dams or vented dams (in the case described, they hypothesize that the dam tipped upon injection of silicone.) They also emphasize the importance of warning patients about possible risks and asking them to sign a release of medical liability. The authors even consider whether deep canal devices should be reclassified under more stringent FDA classification as Class II devices. They also state, “We look with interest to those companies that are developing 3D scanning technology for ear canals (see Azim, 2012, as an example) as we are anxious to discontinue all current recommended methods for taking deep-canal impressions.”
At Lantos Technologies, we aim to provide audiologists and hearing instrument specialists a deep canal ear imaging solution that they can feel confident about with regards to patient safety. Since the scanner system is self-contained, users do not need to worry about impression material migrating past ear dams to the tympanic membrane. Similarly, for patients with large mastoid bowls that need to be packed with multiple ear dams for a traditional impression, there is no worry of unintentionally creating an impossible-to-remove impression.
by Lydia Gregoret, PhD, AuD, F-AAA, CCC-A
Research Audiologist, Lantos Technologies
Leavitt, R, Welch, C, and Thompson, CR, “Invisible in-the-Canal hearing
Aids and Deep Canal Hearing Aid Fittings: Medical and Audiological Concerns,” pages 36-42, Audiology Today, July-August, 2013
(American Academy of Audiology login required to access article on-line.)
Azim, S. “Making a digital impression using 3D ear canal scanning,” Hearing Review, 19(5 Suppl.):8. 2012