[Role of evoked oto-acoustic emission as an objective test of cochlear function]

Evaluation of clinical application of evoked oto-acoustic emission (OAE) as an objective cochlear function test was studied in normal hearing subjects, retrocochlear and cochlear deafness cases. In normal hearing subjects, OAE responses showed good reproducibility while the minimum detectable level of OAE varied between subjects. We found that the interaural difference of minimum detectable level of OAE is the best indicator of cochlear damage. As both OAE and ECochG originate from the hair cells, we compared the behavior of OAE and ECochG in cases with retrocochlear deafness. We found that OAE exhibited the same behaviour as CM in ECochG in these cases. In cases of cochlear deafness, in spite of the recovery of the hearing thresholds to within normal levels, the minimum detectable level of OAE remained at an average of about 4. 4dB higher as compared to normal hearing subjects. This demonstrates that a minimal cochlear damage likely to go undetected by pure tone audiometry is detected by OAE measurement. We conclude that OAE must be added to the growing list of tests in the objective assessment of cochlear function.