Specialty otolaryngology | ICD-10 H90.1, H90.4, H90.7 | |
Unilateral hearing loss (UHL) or single-sided deafness (SSD) is a type of hearing impairment where there is normal hearing in one ear and impaired hearing in the other ear.
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Signs and symptoms
Patients with unilateral hearing loss have difficulty in
In quiet conditions, speech discrimination is no worse than normal hearing in those with partial deafness; however, in noisy environments speech discrimination is almost always severe.
Causes
Known causes include physical trauma, acoustic neuroma, measles, labyrinthitis, microtia, meningitis, Ménière's disease, Waardenburg syndrome, mumps (epidemic parotitis), and mastoiditis.
Prevalence
A 1998 study of schoolchildren found that per thousand, 6-12 had some form of unilateral hearing loss and 0-5 had moderate to profound unilateral hearing loss. It was estimated that in 1998 some 391,000 school-aged children in the United States had unilateral hearing loss.
Profound unilateral hearing loss
Profound unilateral hearing loss is a specific type of hearing loss when one ear has no functional hearing ability (91 dB or greater hearing loss). People with profound unilateral hearing loss can only hear in monaural (mono).
Profound unilateral hearing loss or single-sided deafness, SSD, makes hearing comprehension very difficult. With speech and background noise presented at the same level, persons with unilateral deafness were found to hear only about 30-35% of the conversation. A person with SSD needs to make more effort when communicating with others. When a patient can hear from only one ear, and there are limited possibilities to compensate for the handicap, e.g., changing listening position, group discussions and dynamic listening situations become difficult. Individuals with profound unilateral hearing loss are often perceived as socially awkward due to constant attempts to maximize hearing leading to socially unique body language and mannerisms.
SSD also negatively affects hearing and comprehension by making it impossible for the patient to determine the direction, distance and movement of sound sources. In an evaluation using the Speech, Spatial and Qualities of Hearing Scale (SSQ) questionnaire, SSD results in a greater handicap than subjects with a hearing loss in both ears.
Profound SSD is often confused with Sensory Discrimination Disorder (SDD), a type of Sensory Processing Disorder, and can lead to incorrect processing of sensory information or auditory input during interpersonal communications.
SSD is known to cause:
Management
Learning of the central nervous system by "plasticity" or biological maturation over time does not improve the performance of monaural listening. In addition to conventional methods for improving the performance of the impaired ear, there are also hearing aids adapted to unilateral hearing loss which are of very limited effectiveness due to the fact that they don't restore the stereo hearing ability.
In Germany and Canada, cochlear implants have been used with great success to mostly restore the stereo hearing ability, minimizing the impacts of the SSD and the quality of life of the patient.
Evaluation
As of 2012 there has only been one small-scale study comparing CROS systems.
One study of the BAHA system showed a benefit depending on the patient's transcranial attenuation. Another study showed that sound localisation was not improved, but the effect of the head shadow was reduced.
Hearing issues
School-age children with unilateral hearing loss tend to have poorer grades and require educational assistance. This is not the case with everyone, however. They can also be perceived to have behavioral issues.
People afflicted with UHL have great difficulty locating the source of any sound. They may be unable to locate an alarm or a ringing telephone. The swimming game Marco Polo is generally impossible for them.
When wearing stereo headphones, people with unilateral hearing loss can hear only one channel, hence the panning information (volume and time differences between channels) is lost; some instruments may be heard better than others if they are mixed predominantly to one channel, and in extreme cases of sound production, such as complete stereo separation or stereo-switching, only part of the composition can be heard; in games using 3D audio effects, sound may not be perceived appropriately due to coming to the disabled ear. This can be corrected by using settings in the software or hardware—audio player, OS, amplifier or sound source—to adjust balance to one channel (only if the setting downmixes sound from both channels to one), or there may be an option to outright downmix both channels to mono. Such settings may be available via the device or software's accessibility features. As hardware solutions, stereo-to-mono adapters may be available to receive mono sound in stereo headphones from a stereo sound source, or some monaural headsets for cellphones and VOIP communication may combine stereo sound to mono (though headphones for voice communication typically offer lower audio quality than headphones targeted for listening to music). From the standpoint of sound fidelity, sound information in downmixed mono channel will, in any case, differ from that in either of the source channels or what is perceived by a normal-hearing person, thus technically some audio quality is lost (for example, the same or slightly different sound occurrences in two channels, with time delay between them, will be merged to a sound in the mono channel that unavoidably cannot correspond to the intent of the sound producer); however, such loss is most probably unnoticeable, especially compared to other distortions inherent in sound reproduction, and to the person's problems from hearing loss.