Hearing loss associated with weapons noise exposure: when to investigate an asymmetrical loss

The air conduction thresholds in the right and left ears, and the interaural asymmetry of thresholds at 0.5, 1, 2, 3, 4 and 6 kHz were measured in a group of 225 soldiers exposed to a variety of weapon noise who were referred for assessment because of a deterioration in hearing on routine testing. At 0.5 and 1 kHz the threshold levels rarely exceeded 25 dB and the interaural asymmetry was 10 dB or less in 90 per cent of cases. The degree of hearing loss and interaural asymmetry increased as the frequency increased, with the average loss being significantly greater in the left ear at 2, 3, 4 and 6 kHz. Recommendations are made for the selection of cases of asymmetrical hearing loss exposed to weapon noise which require further investigation to exclude a retrocochlear cause or to define spurious hearing threshold levels.