Abstract
Introduction The question as to whether occupational noise exposure causes symmetrical or asymmetrical
hearing loss is still controversial and incompletely understood.
Objective Two electrophysiological methods (cortical evoked response audiometry: CERA and auditory
steady state responses: ASSR) were used to address this issue.
Method 156 subjects with a well-documented history of noise exposure, a wide range of noise
induced hearing loss (NIHL) and without middle ear pathology underwent both a CERA
and an ASSR examination in the context of an exhaustive medicolegal expert assessment
intended for possible compensation.
Results Whatever the method (CERA or ASSR), the average electrophysiological hearing thresholds
(1-2-3 kHz) are significantly worse in the left ear. The right - left differences
in CERA and ASSR thresholds are strongly correlated with each other. No significant
effect of frequency is found. No correlation is observed between right - left differences
in hearing thresholds and either age or degree of hearing loss.
Conclusion In NIHL, there is an actual average right - left difference of about 2.23 dB, i.e.,
3.2%, the left ear being more impaired.
Keywords
hearing loss - asymmetry - evoked potentials - noise
