**Conflict of interest**

*Advances in Rehabilitation of Hearing Loss*

distortion of sound.

**5. Summary**

the affected ear and normal hearing on the opposite ear are less likely to realize the benefits of hearing aids on the affected ear and are often unable to wear them. Since some degree of auditory function remains in the affected ear, symptoms such as difficulty in hearing and impaired sound localization are milder than in patients with SSD, and, as a result, the beneficial effect of wearing a hearing aid seems to be difficult to perceive subjectively and to detect objectively. In addition, Kumpik et al. reviewed from several studies that horizontal localization by adult humans can adapt to varying degree to asymmetric hearing loss induced by occluding one ear [21]. Therefore, the abilities of sound localization and spatial hearing may be spontaneously restored in some degree in the patients with unilateral mild-to-moderate hearing loss. There do not seem to be any previous reports that examined the effect of hearing aids for hear-

ing disability in patients with unilateral mild-to-moderate hearing loss.

Hearing-related discomfort is also common in ISSHL patients with unilateral moderate hearing loss, but the mechanism may differ from that in patients with unilateral severe-to-profound hearing loss. Patients with moderate hearing loss are more likely to have discomfort with sounds heard on the affected side, that is, increased loudness of noise caused by the recruitment phenomenon or distortion caused by the impairment of frequency selectivity function is unpleasant. Therefore, it is unlikely that a hearing aid will improve excessive loudness and

On the other hand, tinnitus symptoms are more common in patients with mildto-moderate hearing loss due to ISSHL. Tinnitus retraining therapy using a hearing aid as a means of sound therapy has been widely conducted. At present, there is no high-quality evidence from systematic reviews [22], but improvement in the Tinnitus Handicap Inventory or visual analog scales has been widely recognized. In the future, it will be necessary to establish evidence of tinnitus improvement and to evaluate speech comprehension in noise and sound localization as well as hearing-

ISSHL is an important cause of persistent unilateral sensorineural hearing loss that affects thousands of new patients annually in Japan. The problems caused by ISSHL can be categorized into four factors: hearing difficulty, deterioration of spatial hearing, hearing-related discomfort, and tinnitus. The interventions that have been used to treat patients with unilateral hearing loss can be adapted to patients with ISSHL. The expected benefits of interventions for ISSHL patients are shown in **Table 2**. Although there are presently no treatments that provide satisfactory outcomes, CI is possibly the current most effective means of restoring some

**Grade of hearing loss Severe-deaf Mild-moderate Intervention BAHA/CROS CI Conventional HA**

Speech in noise Partially improved Partially improved ? Spatial hearing → Possibly improved ? Discomfort ? ? ?

→*, not improved; ?, not available for applicable investigations.*

*Expected effect of interventions for patients with ISSHL.*

Tinnitus → Improved Improved *BAHA, bone-anchored hearing aid; CROS, contralateral routing of signals; CI, cochlear implant; HA, hearing aid;* 

related discomfort in ISSHL patients with mild-to-moderate hearing loss.

**10**

**Table 2.**

The author has no conflict of interest to declare.
