Role of Conventional Hearing Aid in Single-Sided Deafness

One of the most perplexing hearing conditions that audiologists encounter in their daily practice is single-sided deafness (SSD), or unilateral profound sensorineural hearing loss (SNHL), which is often considered as clinically unaidable hearing. SSD is defined as a condition in which an individual has profound SNHL in one ear, with normal audiological function in the contralateral ear. The deficits and difficulties associated with SSD are underrecognized, mainly due to a lack of public awareness. Hearing loss is regarded as an invisible handicap with a disability that is less noticeable and thus undervalued. In contrast with other paired sensory systems such as vision, the result of unilateral impairment is immediately apparent. Most hearing professionals have a one-dimensional approach to SSD, where only the hearing loss is addressed, though SSD is often known to present with a plethora of symptoms. It would be practical to employ a multidimensional approach in these cases to improve the overall quality of life for each individual. This article discusses some of the important factors that need to be considered to improve success in the overall management of SSD. CLINICAL PRESENTATION OF SSD SSD refers to unilateral profound SNHL where medical management was ineffective, and the patient is referred to an audiologist for rehabilitation. As the name signifies, hearing loss is the most important symptom they present with, often with debilitating tinnitus. In addition to this, SSD significantly impairs spatial hearing, which is dependent on the integration and processing of both monaural and binaural hearing cues. As a result of this, they have poor sound localization, speech perception in noise, access to environmental sounds, selecting/switching attention between talkers, ease of listening, and balance function leading to reduced quality of life.1 The integration of sensory inputs such as vision, hearing, and proprioception is essential to create a mental picture of the space around us, which is commonly referred to as spatial image.2 Sound localization plays a significant role in the balance process as sound information in the environment serves as a reference point for spatial orientation. This aids in the maintenance of balance by creating a three-dimensional map of one’s surroundings. Loss of audio biofeedback may increase the fluctuations in sway velocity, which can lead to postural instability; therefore, auditory stimulation on the impaired/poorer ear may help correct this factor.3 Tinnitus, which is often debilitating in patients with SSD, is another aspect that is frequently overlooked. Tinnitus in SSD has been shown to interfere with speech perception in noise in the non-tinnitus ear. In a patient with a cochlear implant when the processor in the deaf ear is activated, speech perception in noise improves in the non-tinnitus ear, and tinnitus loudness decreases.4–6 Acoustic stimulation on the affected side may not only provide the binaural cues required for sound localization and speech recognition in noise, but it may also improve spatial hearing by reducing tinnitus through central pathways. This supports the idea that SSD patients with tinnitus may benefit more from acoustic stimulation than SSD patients without tinnitus. Conversely, tinnitus severity following unilateral sudden SNHL likely decreases over time in a subset of patients, even if left untreated, due to spatial reorganization of the auditory cortex in both hemispheres.7,8 Some SSD patients may be able to compensate for the loss of binaural auditory cues by improving both spatial and temporal central auditory processing over time.7 CLINICAL MANAGEMENT OPTIONS FOR SSD Several interventions have been proposed to improve the sound localization and speech recognition of SSD patients in noisy environments. With the introduction of contralateral routing of signal (CROS) and bilateral CROS (BiCROS) hearing aids, traditional SSD rehabilitation relied on rerouting acoustic signals from the poorer ear to the normal/better ear for processing. The reasoning behind rerouting the sound signals is that there is insufficient functional hearing on the affected side to augment. These hearing aids are the first choice of rehabilitation because they provide a noninvasive approach to improving access to signals of interest in SSD. In addition, surgical and non-surgical bone-anchored hearing aids (BAHA), which were originally designed for conductive or mixed hearing losses, have now been extended to SSD patients. The aforementioned interventions may improve speech recognition in noisy environments, at least subjectively, especially when speech is presented to the deaf ear. As the deaf ear is not stimulated, neither CROS nor the BAHA systems address the imbalance and tinnitus experienced by these individuals. More recently, cochlear implantation for unilateral deafness has gained much importance, intending to control tinnitus and then restore binaural hearing.5 Since it is an invasive procedure, this is the last resort for most people with SSD who have not benefitted from the above-mentioned interventions. Conversely, noninvasive management options such as conventional amplification for the impaired ear would benefit the SSD population in the same manner as cochlear implantation by increasing the likelihood of binaural cues. In clinical practice, restoring binaural hearing should be the default option for SSD patients. Implications of conventional versus contralateral hearing devices Conventional hearing aids provide significant benefits in some individuals with SSD since they address most disabilities faced by these patients. Not all individuals with SSD see these benefits when given a hearing aid trial. The age of the patient, occupation, listening needs and personality, along with the associated symptoms of SSD, are the major factors that determine the overall success of hearing aid therapy in these individuals. Due to the additional benefits that hearing aids provide, a hearing aid trial should be given to all individuals with SSD before contemplating therapy with CROS hearing aids. Because personality plays a significant role in predicting whether a therapeutic sound is a positive or negative moderator.9 CROS, Bi-CROS hearing devices, and BAHA systems have a place in this population, but only after the benefits of conventional amplification on the poor ear have been explored. The following are some of the benefits of conventional hearing aids in this population: better sound-source localization as a consequence of binaural processing cues and lateralization from the loudness cue provided by the conventional amplification device tinnitus reduction by providing auditory stimulation to the few remaining functional hair cells in the affected ear improved balance function by providing auditory spatial cues from the affected side decreased listening effort and better speech perception in noisy places minimizing auditory deprivation (Cross-modal reorganization is a process where other intact senses compensate for hearing loss. This cortical compensation has been observed in individuals with SSD, as with other forms of hearing loss. Studies have shown that intervention with amplification has been demonstrated to facilitate reversal in cross-modal re-organization of the auditory cortex, thereby promoting typical cortical organization and functioning, and thus providing cognitive benefit.).10,11

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