There is an increasing global recognition of the negative impact of hearing loss, and its association to many chronic health conditions. The deficits and disabilities associated with profound unilateral hearing loss, however, continue to be under-recognized and lack public awareness. Profound unilateral hearing loss significantly impairs spatial hearing abilities, which is reliant on the complex interaction of monaural and binaural hearing cues. Unilaterally deafened listeners lose access to critical binaural hearing cues. Consequently, this leads to a reduced ability to understand speech in competing noise and to localize sounds. The functional deficits of profound unilateral hearing loss have a substantial impact on socialization, learning and work productivity. In recognition of this, rehabilitative solutions such as the rerouting of signal and hearing implants are on the rise. This review focuses on the latest insights into the deficits of profound unilateral hearing impairment, and current treatment approaches.

Objective: To compare the benefit of wireless contralateral routing of signal (CROS) technology to bone-anchored implant (BAI) technology in monaural listeners. Study Design: Prospective, single-subject. Setting: Tertiary academic referral center. Patients: Adult English speaking subjects using either a CROS hearing aid or BAI as treatment for unilateral severe-profound hearing loss. Interventions: Aided performance utilizing the subjects BAI or CROS hearing device. Main Outcome Measures: Outcome measures included speech-in-noise perception using the QuickSIN^™ (Etymotic Research, Elkgrove Village, IL, 2001) speech-in-noise test and localization ability using narrow and broadband stimuli. Performance was measured in the unaided and aided condition and compared with normal hearing controls. Subjective outcomes measures included the Speech Spatial and Qualities hearing scale and the Glasgow Hearing Aid Benefit Profile. Results: A significant improvement in speech-in-noise performance for monaural listeners (p < 0.0001) was observed, but there was no improvement in localization ability of either CROS or BAI users. There was no significant difference between CROS and BAI subject groups for either outcome measure. BAI recipients demonstrate higher initial disability and handicap over CROS hearing aid users. No significant difference was observed between treatment groups for subjective measures of post-treatment residual disability or satisfaction. Conclusions: Our data demonstrate that both CROS and BAI systems provide significant benefit for monaural listeners. There is no significant difference between CROS or BAI systems for objective measures of speech-in-noise performance. CROS and BAI hearing devices do not provide any localization benefit in the horizontal plane for monaural listeners and there is no significant difference between systems.

In recent years, an increasing research effort has been directed toward remediation of single-sided deafness. Contralateral routing of signal (CROS) is the longest standing rehabilitation solution for individuals with single-sided deafness. The primary goal of CROS technology is to transfer the signal received at the deaf ear to the better hearing ear, thereby reducing the impact of the acoustic head-shadow. This allows for individuals with single-sided deafness to regain access to sounds located at the deaf ear. The hearing deficits associated with single-sided deafness are often debilitating. While surgical management of single-sided deafness is on the rise, CROS hearing aids offer a nonsurgical option to compensate for some of the deficits that occur when a listener is limited to a single ear. Limitations of early CROS devices resulted in poor adoption and acceptance in those with single-sided deafness. Following significant advances in both design and technology, the acceptance of CROS devices has increased in recent years. This paper reviews relevant literature in CROS application for the management of single-sided deafness. Technological advances, benefits, limitations, and clinical considerations are also reviewed in this article.

Objective: Eye tracking technology has been employed in assessing ocular motor and vestibular function following vestibular and neurologic conditions, including traumatic brain injury (TBI). Assessments include tests that provide visual and motion (rotation) stimuli while recording horizontal, vertical, and torsional eye movements. While some of these tests have shown diagnostic promise in previous studies, their use in clinical practice is limited by the lack of normative data. The goal of this study was to construct normative reference ranges to be used when comparing patients' results.Methods: Optokinetic response, subjective visual horizontal and vertical, and rotation tests were administered to male and female volunteers, ages 18‐45, who were free from neurological, vestibular disorders, or other head injuries. Tests were administered using either a rotatory chair or a portable virtual reality‐like goggle equipped with video‐oculography.Results: Reference values for eye movements in response to different patterns of stimuli were analyzed from 290 to 449 participants. Analysis of gender (self‐reported) or age when grouped as pediatric (late adolescent; 18‐21 years of age) and adult (21‐45 years of age) revealed no effects on the test metrics. Data were pooled and presented for each test metric as the 95% reference interval (RI) with 90% confidence intervals (CI) on upper and lower limits of the RI.Conclusions: This normative database can serve as a tool to aid in diagnosis, treatment, and/or rehabilitation protocols for vestibular and neurological conditions, including mild TBI (mTBI). This database has been cleared by the FDA for use in clinical practice (K192186).Level of evidence: 2b

Objective: To compare the effectiveness of current contralateral routing of signal technology (CROS) to bone-anchored implants in experienced bone-anchored implant users with unilateral severe-profound sensorineural hearing loss. Design: Prospective, within-subject repeated-measures comparison study. Setting: Tertiary referral center. Patients: Adult, English-speaking patients (n = 12) with severe-profound unilateral sensorineural hearing loss implanted with a bone-anchored implant for the indication of single-sided deafness. Intervention: Subjects were fitted with contralateral routing of signal amplification and tested for speech in noise performance and localization error. Outcome Measures: Speech perception in noise was assessed using the BKB-SIN test materials. Localization was assessed using narrow band noises centered at 500 and 4000 Hz, as well as a broadband speech stimulus presented at random to the front hemifield by 19 speakers spatially separated by 10 degrees. Results: There was no improvement in localization ability in the aided condition and no significant difference in performance with CROS versus bone-anchored implants (BAI). There was a significant improvement in speech in noise performance for monaural listeners in the aided condition for speech poorer ear/noise better ear, speech front/noise front, and speech front/noise back. No significant difference was observed on performance with CROS versus BAI subjects. Conclusion: Contrary to earlier studies suggesting improved performance of BAIs over CROS, the current study found no difference in performance in BAI over CROS devices. Both CROS and BAI provide significant benefit for monaural listeners. The results suggest that noninvasive CROS solutions can successfully rehabilitate certain monaural listening deficits, provide improved hearing outcomes, and expand the reach of treatment in this population.