“…The sensorineural hearing loss in HDR patients can be both symmetric or asymmetric, and as tested by auditory brainstem response (ABR), conditioned orientation reflex tests or pure tone audiometry, it ranges in level from 40 dB to 105 dB (Bilous et al, 1992;Fujimoto et al, 1999;Hasegawa et al, 1997;Lichtner et al, 2000;Muroya et al, 2001). Although it is clear that hearing loss in HDR is usually somewhat more severe at the higher end of the frequency spectrum Muroya et al, 2001), no systematic audiometric evaluation has yet been made, and the exact pathophysiological mechanism causing the hearing defect remains largely unknown.…”