Noise-induced otoacoustic emission loss with or without hearing loss

The association between audiometric hearing thresholds and click-evoked otoacoustic emission (CEOAE) spectral properties was examined in 129 adult subjects with and without a noise-induced hearing loss (NIHL). Subjects were grouped according to their "beginning of hearing loss frequency" and their exposure to hazardous noise. Emissions were recorded with an ILO88 Otodynamic Analyzer (Version 2.9) used in the default mode. CEOAE levels decreased as the hearing threshold increased at each of the test frequencies (1,2,3, and 4 kHz). At frequencies where hearing thresholds were worse than 20 dB HL, CEOAEs could not be recorded. Thus as the "beginning of hearing loss frequency" decreased, the frequency range of the emissions became narrower. The hearing threshold for which emissions were not recorded varied significantly between subjects, such that even at frequencies where the hearing threshold was 0 dB HL emissions were not always observed. Noise-exposed, normal-hearing subjects had reduced overall CEOAE power with a narrow frequency range as compared with normal-hearing, nonexposed to noise subjects. For our test conditions, the presence of CEOAEs necessarily suggests hearing thresholds of 20 dB HL or less at the corresponding frequency. A lack of emissions does not necessarily indicate hearing thresholds beyond 20 dB HL.