Iris pigmentation and susceptibility to noise-induced hearing loss

Abstract

The purpose of this retrospective study is to examine the possible association between iris pigmentation and susceptibility to noise-induced hearing loss in 2407 noise-exposed workers. The workers were between 16 to 65 years of age and were exposed to 2 to 42 years of work-related noise. Results demonstrated that dark-eyed workers presented a greater percentage of normal pure-tone thresholds than fair-eyed workers. Fair-eyed workers had threshold averages of 25.1 dB (right ear) and 26.0 dB (left ear) at 3, 4, and 6 kHz, which were significantly worse than workers with dark irises, with threshold averages of 15.8 dB and 17.2 dB in the right and left ear, respectively (p<0.01). Fair-eyed workers with less than 10 years of noise exposure had the same audiometric pattern as the dark-eyed workers exposed for more than 10 years. Workers not exposed to noise did not present significant differences in their audiometric pattern as a function of eye colour. These results suggest that iris pigmentation may be an additional indication of susceptibility to noise-induced hearing loss.

Audiogram Comparison of Workers from Five Professional Categories

“…The asymmetry of noise-induced hearing loss was already observed in previous studies [ 28 – 30 ]. The causes for this asymmetry can be attributed to the cortical pathways, specifically to the more pronounced efferent auditory system on the right side, which reduces the susceptibility of the right ear to cochlear insult, to the head shadow effect, and to physiological differences [ 29 , 30 ].…”

Genetics of human iris colour and patterns

“…There seems to be little support to the idea that iris pigmentation might influence visual acuity in low light environments, though albinism is an exception with developmental ocular problems evident in loss of melanin synthesis capacity. However, there are reported eye colour effects on reaction time and the involvement in particular sports (Rowe and Evans, 1994), associations with shyness evident in childhood (Coplan et al., 1998), links to noise induced hearing loss (Da Costa et al., 2008), and sexual selection (Frost, 2006). There may have been coselection for lightening of pigmentary traits in humans but evidence from haplotype analysis comparing Dutch and Mediterranean population samples has been presented to suggest that blue eye colour has only arisen once during the past 10 000 yr, again apart from albinism, as a founder mutation shared by diverse European populations (Eiberg et al., 2008).…”

Recent findings and emerging questions in cochlear noise injury

“…Retrospective human studies of noise-exposed workers stratified by eye color have produced quite mixed results (Attias et al, 1985; Cunningham et al, 1982). However, a recent study of a large sample of metal workers (Da Costa et al, 2008) obtained a ~9 dB sensitivity difference between ‘dark-eyed’ and ‘fair-eyed’ subjects having a history of moderate work-related noise exposure. Animal data bearing on this issue are inconclusive, and often have relied on sub-optimal genetic controls.…”