Measurements of click-evoked otoacoustic emission in industrial workers with noise-induced hearing loss.

Click-evoked otoacoustic emission (c-EOAE) was analysed in a group of 122 males (= 244 ears) occupationally exposed to industrial noise levels of 89-94 dB (A). The highest intensity of cochlear responses was observed at 1 and 2 kHz, while at the higher frequencies (3-4 kHz), c-EOAE spectrum was contracted proportionally to the level of the hearing loss and duration of occupational exposure to noise. If hearing loss in pure-tone audiometry exceeded 30 dB HL at 1 kHz and 40 dB at 2 and 4 kHz, c-EOAE was absent. The analysis of the relationship between c-EOAE spectrum and hearing threshold in pure-tone audiogram showed correlation (R = 0.43 to 0.48, at p < 0.01) between distribution of emission energy and hearing threshold at the same range of frequencies. It was found that the c-EOAE amplitudes as well as the values of c-EOAE energy in the noise-exposed people were lower by about 3 dB SPL than in the controls, especially at 4 kHz even in cases of pure-tone hearing thresholds < or = 20 dB HL. This study indicates that, owing to c-EOAE, it is possible to detect a slight noise-induced cochlear lesion which may be overlooked in pure-tone audiometry.