1. Introduction
“Two hearing aids work better than one” has been the conventional principle in hearing rehabilitation. Clinicians often recommend bilateral hearing aids to reduce the risk of auditory deprivation in the unaided ear.1-4 Patients who wear two hearing aids can easily judge where sound is coming from.5 However, in cases of asymmetrical hearing loss (AHL), the fitting strategies are unclear and it is tricky to accomplish satisfactory binaural hearing with either monaural or binaural amplification.
Although Briskey’s 60 dB HL rule to fit the ear with average threshold closer to 60 dB are simple for clinicians,6 they tend to underestimate possible advantages of wearing two hearing aids. In addition, Mueller and Hall 7 argued that the aided threshold values, not unaided thresholds, should determine whether the patient or the ear is a reasonable candidate for a hearing aid. Current understanding is that every hearing-impaired person could be a candidate for hearing aids and that good understanding of individual’s social communication needs should be the determining factor for successful hearing aid use. Of course, good understanding implies a need for parameters that can predict which patients will successfully use of hearing aids, but there has been no available parameters.6, 8
We often encounter AHL cases in which binaural symmetry cannot be accomplished with bilateral hearing aids. In some situations, in which only one hearing aid is available for patients with AHL, the 60 dB HL rule has been a simple guideline, but it provides limited information to decide which ear is needed. This is commonly seen in South Korea because of the coverage system of National Health Insurance Service (NHIS) and the hearing aid market. Because little research has reported the choice of ear (better or worse) for monaural amplification in patients with AHL, we have struggled to determine which ear should be fitted for a hearing aid. In many cases of AHL, we have prescribed a hearing aid for the worse ear, empirically based on audiometric data, surveys, and patient interviews. However, we have encountered cases where the aided side changed from the worse to the better during the process of counseling and fitting. This discrepancy between the clinician’s recommendation and patient acceptance has been a big problem. In addition, AHL patients have reported a wide range of satisfaction.
Therefore, our aims in this study were to evaluate the outcomes of hearing-aid use for AHL patients aided in their worse ear only and to identify any predictable factors that might influence those outcomes. In this study, we defined AHL as hearing loss with an interaural difference of 15 dB HL or greater in the four-frequency (0.5, 1, 2, and 4 kHz) pure-tone average thresholds (PTA4),9and we further classified it into three subtypes for a more detailed analysis.