Table 1 Summary of literature on asymmetric NIHL
First authors & year | Design | Participants | Calculation Methods | Asymmetry Criteria | Outcomes | Additional factors considered |
|---|---|---|---|---|---|---|
May et al. 1990 [101] | Case series | 49 dairy farmers 94% male, 6% female mean age 43.5 average farming 29.4Â years | 0.5,1, 2, 3Â kHz (PTA) 3, 4, 6Â kHz (HFA) | >20Â dB average hearing loss in either ear | Left ear is more severely affected in both groups. 37% abnormal PTA, 65% abnormal HFA. Significant association with years worked and age. | presbycusis, small sample. |
Ostri et a1. 1989 [102] | Case series | 95 orchestral musicians 80 males, 15 females age 22–64 | 0.125, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, 8 kHz (PTA) | >20 dB average hearing loss in either ear | 44% of musicians had hearing impairment attributed to occupational noise exposure. Significant poorer hearing on the left ear found at higher frequencies among violinist. | instrument played, side of orchestral band, previous noise exposure |
Cox et a1 1995 [63] | Case series | 235 soldiers with past weapon noise exposure age 16–55 | 0.5,1, 2, 3,4, 6 kHz (average single frequency threshold) | Interaural difference = asymmetry >10 dB | 67% asymmetry at 4 kHz. Average hearing loss and interaural asymmetry increased with frequency. | handedness, emotional immaturity, motivation for army service, use of ear defenders |
Pirila et al. 1992 [109] | Cross-sectional study | 3487 random people 1640 males, 1847 females 3 age groups (5–10,15–50, >50) | 0.125, 0.25,0.5,1, 2, 3, 4, 6, 8 kHz (average single frequency threshold) | Interaural difference = asymmetry >0 dB | The inferiority of hearing in the left ear at 4 kHz seems to be assiciated with noise damage. The average interaural difference at 4 kHz was more marked in age 15–50. | shooting history occupational noise exposure |
Pirila et al. 1991 [98] | Cohort study | 28 non-shooting normal HL 10 males, 18 females age 17–29 exposure to broad band noise 88–91 dB for maximum 8 h | 4 kHz (average single frequency threshold) | determine TTS after noise exposure | TTS was greater in the left ear than the right. Negative correlation between pre-exposure threshold level. | rely on history, samll sample size. |
Chung et al. 1983 [95] Audiology | Case series | 1461WCB claims for NIHL no head injury, no ear surgery age 36–82 | 2 kHz (average single frequency threshold) | >20 dB | 4.7% has asymmetry, suggesting damage toward apex. 82.6% has worse hearing thresholds in the left ear. 2 kHz is lateral difference in susceptibility to noise damage. | limited frequency considered |
Nageris et al. 2007 [103] | Case series | 4277 army personnel files age 16–55 | 3–6 kHz (PTA) | mild loss = 25–40 dB HL moderate loss = 41–60 dB HL severe loss = 61–90 dB HL asymmetry = different grade | 50% symmetrical. 34.2% left asymmetrical NIHL. 16.3% right asymmetrical NIHL | No significant differences in: age, sex, type of noise, protection, length of exposure, handedness, acoustic reflex. |
Simpson et al. 1993 [202] | Correctional study | 1667 audiometric records of 10 industries 1367 males, 300 females mean age 32.7 and 33.5 | 2, 3,4 kHz (average threshold) | Interaural difference = L-R laterality >5 dB | 80% unilateral with left 42% and right 38%. Baseline hearing asymmetry appears to be a precursor to unilaterality with 63% in the better ear. | no recordof otologic background, no noise exposure history. |
Hong et al. 2005 [60] | Cohort study | 623 operating engineers mean age 42.96 male 92% | 0.5,1, 2, 3, 4, 6, 8Â kHz (PTA) | Asymmetry: >15Â dB at 0.5,1,2Â kHz >30Â dB at 3,4, 6Â kHz | 19% of workers had asymmetrical hearing loss. Significant poorer hearing in the left ear, especially at 4 and 6Â kHz | Use of hearing protection devices resulted in better hearing but in low use |
Fernandes et al. 2010 [94] | Case series | 208 clients with hearing loss for compensation; age 36–73 203 males, 5 females | 0.25–6 kHz (hearing threshold) | Asymmetry: >10 dB for 2 frequencies >15 dB for one frequency | 22.6% of clients had asymmetrical hearing loss. Left side had greater loss in 60% of cases. | MRI showed no central pathology |
Chung et al. 1983 [95] J Occu Med | Cohort study | 244 shingle sawyers all males age 20–59 | 0.5,1, 2, 3, 4, 6, 8 kHz (average single frequency threshold) | not defined | Asymmetry of hearing loss is significant but small compared to general industrial population especially at low frequencies. | 101/244 had history of shooting. Hearing protection not well-defined. Small difference of 2.8 dB to left side. |
Alberti et al. 1979 [1] | Case series | 1873 patients with hearing loss for WCB | 0.5,1, 2, 4Â kHz (PTA) | asymmetry >15Â dB | 15% had asymmetrical hearing loss 5.2% attributed to noise exposure | no treatable disorder found after extensive investigations. |
Robinson et al. 1985 [111] | Case–control series | 63 subjects with noise exposure (94 dB) of lOrs 97 normal control subjects | 0.5–6 kHz (hearing threshol) | Interaural difference = L -R asymmetry >15 dB | 10% left-right difference at 4 kHz. | small sample variable audiogram shapes |
Berg et al. 2014 [92] | Cohort study | 355 young workers age 29–33 68.5% men follow-up <16 years | 0.5,1, 2, 3, 4, 6, 8 kHz (hearing threshold) | not defined | Asymmetry at >2 kHz in men Increased asymmetry with increased levels of hearing loss Asymmetry larger in men | Asymmetry varies with shooting exposure No head shadow effect on asymmetry |
Dobie et al. 2014 [91] | Case–control series | 1381 men with noise 80–102 dB 663 men with noise <80 dB occupational noise exposure | 0.5,1, 2, 3 kHz (PTA) 3,4, and 6 kHz (PTA) | not defined | no significant asymmetry attributable to current occupational noise exposure Left ears were 1–2 dB worse than right ears for both groups |  |
Dufresne et al. 1988 [96] | Case series | 602 WCB claims | 0.25–8 kHz (hearing threshold) | not defined | more hearing loss in left ear compared to right ear (5–30 dB) in truck drivers, but not significant for others | small sample of truck drivers (n = 10) |
Segal et aI. 2007 [99] | Cohort study | 429 workers 241 (56.2%) with noise exposure (hearing threshold) 188 patients (43.8%) without 79.3% men with SNHL (>29 dB) | 0.25–8 kHz (hearing threshold) | not defined | in noise exposed group, left ear has higher threshold in men. no significant difference left-right in group wihout noise exposure. |  |
Zapala et al. 2012 [203] | Case series | Case series n = 5661 benign assymmetry n = 85 vestibular schannoma | 0.25–8 kHz (PTA) | asymmetry < 20 dB | Greater asymmetry in self-reported noise exposure history. Largest asymmetry at frequencies >1 kHz Asymmetry increased with age | Small differences in asymmetry: Males (5.14 dB) at 3 and 4 kHz Females (5.8 dB) at 4 kHz |
Royster et al. 1980 [90] | Cohort study | industrial noise exposure 14186 (75.9% male) | 0.5–6 kHz (hearing threshold) | not defined | right ears are significantly lower threshold Asymmetry is largest for frequecies >2 kHz | Mean differences in asymmetry re small (l–5 dB). |
Kannan et al. 1974 [100] | Review | n = 172 50% male | l–8 kHz (mean threshold) | difference L-R >0 dB | Right ear significantly better hearing than left in males only | No data about the extend of noise exposure |