Lateral differences in susceptibility to noise damage.

Usually equal noise exposure is considered to cause symmetrical hearing loss. In studying 1 461 audiometric records of claims for noise-induced hearing loss, it was found that 69 (4.7%) had a well-defined pattern of hearing loss in which only 2 kHz is asymmetrical by 20 dB or more. Audiograms of this type suggest that the cochlea of the worse ear has been damaged more extensively towards the apex. Of the 69 cases with a 2-kHz asymmetry, 82.6% had worse hearing thresholds in the left ear at 2 kHz. In 50% of the 69 cases, the asymmetry could not be accounted for even after the examination of their medical, occupational and nonoccupational histories. It is believed that the asymmetry at 2 kHz is a manifestation of a lateral difference in susceptibility to noise damage and that the left ear is the more susceptible one in the majority of cases.