Can otoacoustic emissions indicate susceptibility to noise-induced hearing loss in individual ears?

Otoacoustic emissions (OAEs) can potentially be used to identify normal-hearing individuals who are susceptible to imminent noise-induced hearing loss. Until now, there has been no way to monitor an individual’s susceptibility dynamically as it varies due to physiological and environmental factors. Although it is known that groups of normal-hearing noise-exposed people have lower than average levels of OAEs, such data have never been used to predict future hearing loss in the same individuals. Here, we discuss two studies where the OAEs and hearing thresholds of individuals were measured before and after hazardous noise exposure. Individuals with normal hearing and low-level or absent OAEs at baseline were at increased risk for acquiring noise-induced hearing loss after the noise exposure. This supports the theory that OAEs can reflect incipient inner-ear damage undetected by standard behavioral hearing tests. Furthermore, OAE efferent strength measures may be predictors of NIHL in humans. The animal data are promising, but developing an efficient OAE test that reliably distinguishes a strong efferent reflex from a weaker one in humans is challenging. [Work supported by ONR & USAMRMC].