HEARING AID MORPHOLOGY APPLICATIONS
OF VIDEO OTOSCOPY
© 1995; Roy F. Sullivan, Ph.D.(rev. 10/11/1995)
As applied to hearing aids, the term MORPHOLOGY is used to indicate the physical structure, in contrast to the electro-acoustic sub-structure, of the hearing instrument. At the gross level, MORPHOLOGY refers to the basic configuration of the hearing aid; i.e. custom full shell / concha; half shell; canal; mini-canal, completely-in-canal (CIC); behind-the-ear (BTE); conventional / body-worn; eyeglass.
At the intermediate or acoustic coupling level, hearing aid MORPHOLOGY includes the custom hearing aid shell, faceplate and venting the BTE earmold, earhook, tubing and venting. [Sullivan, R, "An acoustic coupling-based classification system for hearing aid fittings"; HEARING INSTRUMENTS, Part 1: Vol 36, #9, September 1985; Parts 2 and 3: Vol 36 #12, December, 1985; and "Acoustic coupling classification system and custom hearing aids. Introduction and overview"; STARKEY REPORTS IN HEARING INSTRUMENTS AND TECHNOLOGY, Vol 2, #1, Fall, 1990. ]
At the fine level, MORPHOLOGY for both custom and BTE instruments includes transducer ports and extension tubing, battery compartments (BC), gain control (GC) knobs, external switches and ancillary structures for custom canal instrument retention such as the canal lock, tragal notch tongue (TNT) and anti-tragal lip (ATL).
Stedman's medical dictionary defines COSMESIS as "A regard in therapeutics...for the appearance of the patient...". Gross morphology considerations determine the cosmetic impact of a fitting. While audiologically derived and needs-based goals are primary in any hearing aid fitting, technology has advanced to the point of providing morphological alternatives to achieve the same psycho- and socio-acoustic end result. Video otoscopy is most helpful in evaluating the anatomical terrain of the ear as a repository for corrective amplification and selecting a hearing aid morphology which is both electro-acoustically and cosmetically appropriate. VO is an effective mirror to provide patients with a dynamic reflection of their hearing instrument fitting cosmetic impact.
In the fitting of hearing aids, there is a logical hierarchy of morphologically-based desiderata, transcending the cosmetic, which must be respected in order for long-term successful use to prevail - despite the audiological appropriateness and excellence of the hearing instrument electro-acoustic response characteristics.
1. PHYSICAL DISCOMFORT SHOULD NOT LIMIT WEARING TIME.
The world's most audiologically appropriate and cosmetically acceptable hearing aid fitting will be rejected if the number of in-use hours is restricted by physical pain or discomfort. Consequently, the absence of hearing aid-induced otalgia is an overarching consideration. VIDEO OTOSCOPY (VO) has been extremely helpful in viewing and diagnosing sites of contact irritation caused by the acoustic coupling morphology; i.e. custom hearing instrument shells, from full concha through CIC, and BTE cases, earhooks and earmolds. The observed site of lesion dictates the location, nature and extent of required hearing aid morphological remediation.
2. THERE SHOULD BE NO OSCILLATORY OR SUB-OSCILLATORY FEEDBACK AT PRESCRIBED IN-USE GAIN LEVELS.
If the patient is comfortable with the properly inserted hearing instrument morphology but is constrained to reduce the gain control below preferred listening level (PLL) in order to avoid feedback, an otherwise audiologically appropriate fitting will also be unsuccessful. Incorrectly inserted or extruding hearing aids can be demonstrated with VO.
3.THE PATIENT SHOULD BE ABLE TO INSERT, REMOVE, OPERATE AND MAINTAIN THE HEARING INSTRUMENT IN AN EFFECTIVE MANNER.
If the hearing aid is inserted improperly, mismatched surface contact can create pressure points which can result in acute epidermal lesions as well as acoustic feedback through the expanded slit leak. Forced insertion and removal can also cause skin irritation. Lack of hygiene can cause contact dermatitis as well as leave an organic residue which may occlude receiver tube, receiver, vent, microphone and earmold. Using both video oto-endoscopic (VOE) and video oto-macroscopic (VOM) modes of viewing, VO is also highly effective as a teaching medium for patients to acquire aid operation skills and to apply and understand the need for instrument maintenence
4. THE PATIENT SHOULD UNDERSTAND THAT, DURING ITS USABLE LIFE, A HEARING AID WILL REQUIRE OCCASIONAL IN-OFFICE AND/ OR LABORATORY MAINTENANCE.
The patient should be counseled to this fact at time of fitting. However,
this is often forgotten when the hearing aid malfunctions. VO can be used to identify and highlight for the patient the morphologically-based reasons for local or factory service.