Hearing Loss Asymmetry due to Chronic Occupational Noise Exposure.

Objective:To determine whether occupational noise exposure causes symmetrical or asymmetrical hearing loss.Study Design:Retrospective Case Series.Setting:Otorhinolaryngology Specialist Centre.Patients:Seven hundred forty-four reports for occupational noise-induced hearing loss (NIHL) compensation were analyzed. Subjects with at least 40% of their total hearing loss due to occupational NIHL were included. Claimants with any confounding factor that could cause asymmetric hearing loss such as history of shooting, head, or ear trauma were excluded. With the strict inclusion criteria, 83 subjects were included in the study. Claimants with 40%, 60%, and 80% occupational NIHL of their total hearing loss were compared.Intervention(s):None.Main Outcome Measure(s):The left ear hearing threshold compared with the right ear hearing threshold (dB) at the frequencies 0.5 to 8kHz.Results:In the total group, the left ear hearing threshold was statistically significantly higher compared with the right ear at 3kHz (2.41dB). In the subgroups 60% and 80% occupational NIHL of total hearing loss, the left ear hearing threshold was statistically significant higher compared with the right ear at 3kHz, respectively, 3.81dB and 5.53dB and 4kHz, respectively, 2.86dB and 5.53dB. An asymmetry of more than 10dB at 3 and 4kHz was observed in 39% and 30% of the subjects respectively. In these cases, the vast majority had more pronounced hearing loss in the left ear.Conclusion:Findings of this study further indicate that the left ear is more susceptible to noise exposure compared with the right ear.