Unilateral hearing loss
|Unilateral hearing loss|
|Classification and external resources|
|ICD-10||H90.1, H90.4, H90.7|
Signs and symptoms 
Patients with unilateral hearing loss have difficulty in
- hearing conversation on their impaired side
- localizing sound
- understanding speech in the presence of background noise.
In quiet conditions, speech discrimination is approximately the same for normal hearing and those with unilateral deafness; however, in noisy environments speech discrimination varies individually and ranges from mild to severe.
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 impairment when one ear has no functional hearing ability (91dB 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 in background noise 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 is able to 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.
SSD also negatively affects hearing by making it more difficult 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 patients actually perceived a greater handicap than subjects with a hearing loss in both ears.
SSD is known to cause:
- Frequent headaches, stress
- Social isolation
- Appearance of anxiousness even in low noise situations
- Trouble figuring out where sounds are coming from.
- Variable light dizziness
- Trouble paying attention to what people are saying: "evasive" behaviour.
- Misdiagnoses as ADHD
- Seeming lack of awareness of other peoples personal space and moods
- Lack of sound depth: any background noise (in the room, in the car) is flat and wrongly interpreted by the brain. The effect is similar to what happens when trying to hear someone speaking in a noisy crowd on a mono TV. The effect is also similar to talking on the phone to someone who is in a noisy environment (see also: King-Kopetzky syndrome)
- Inability to filter out background noise or selectively listen to only the important portion of the noise in the environment.
- For sensorineural hearing loss, the lack of input coming from the damaged sensory apparatus can cause "ghost beeps" or ringing/tinnitus as the brain attempts to interpret the now missing sensory data. The frequency and the volume of the noise can increase according to one's physical condition (stress, fatigue, etc.). This can aggravate social problems and increase the difficulty of speech comprehension.
- Talking loudly or "broadcasting": the affected person cannot perceive the volume of his or her voice relative to other people in the same room or close company, resulting in being characterized by others (who may be located beyond normal auditory range) as domineering or boorish
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 specifically suited to unilateral hearing loss.
Contralateral Routing of Signals (CROS) hearing aids are hearing aids that take sound from the ear with poorer hearing and transmit to the ear with better hearing. There are several types of CROS hearing aid:
- conventional CROS comprises a microphone placed near the impaired ear and an amplifier (hearing aid) near the normal ear. The two units are connected either by a wire behind the neck or by wireless transmission. The aid appears as two behind-the-ear hearing aids and are is sometimes incorporated into eyeglasses.
- CIC transcranial CROS comprises a bone conduction hearing aid completely in the ear canal (CIC). A high-power conventional air conduction hearing aid fits deeply into the patient’s deaf ear. Vibration of the bony walls of the ear canal and middle ear stimulates the normal ear by means of bone conduction through the skull.
- BAHA transcranial CROS Bone Anchored Hearing Aid (BAHA): a surgically implanted abutment transmits sound from the deaf ear by direct bone conduction and stimulates the cochlea of the normal hearing ear.
- Intraoral bone conduction which uses bone conduction via the teeth. One component resembles a conventional behind-the-ear hearing aid that wirelessly connects to a second component worn in the mouth that resembles a conventional dental appliance.
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 have poorer grades and require educational assistance. They are also perceived to have behavioral issues.
When wearing stereo headphones, people with unilateral hearing loss can hear only one channel, hence only half of the components of the music, e.g., bass or piano, but not both (although most modern recordings feature amplitude difference in instruments between the channels, rather than complete silence in one channel and full volume on the other, with respect to one specific instrument). The need for headsets for cellphones and VOIP communication has made monaural headphones, which often combine stereo to mono sound, readily available to solve the problem. Stereo headphones may also be connected to a sound source with a stereo-to-monaural adapter to achieve a similar effect (the two stereo channels going into one headphone).
Some portable music players, such as the iPhone from Apple, have accessibility features which allow users to change the sound to mono.
See also 
- Sargent EW, Herrmann B, Hollenbeak CS, Bankaitis AE (July 2001). "The minimum speech test battery in profound unilateral hearing loss". Otol. Neurotol. 22 (4): 480–6. PMID 11449104.
- Welsh LW, Welsh JJ, Rosen LF, Dragonette JE (December 2004). "Functional impairments due to unilateral deafness". Ann. Otol. Rhinol. Laryngol. 113 (12): 987–93. PMID 15633902.
- Lee DJ, Gómez-Marín O, Lee HM (August 1998). "Prevalence of unilateral hearing loss in children: the National Health and Nutrition Examination Survey II and the Hispanic Health and Nutrition Examination Survey". Ear Hear 19 (4): 329–32. PMID 9728728.
- Christensen L, Richter GT, Dornhoffer JL (Feb 2010). "Update on bone-anchored hearing aids in pediatric patients with profound unilateral sensorineural hearing loss". Archives of otolaryngology - head & neck surgery 136 (2): 175–7.
- Bess FH, Tharpe AM (February 1986). "An introduction to unilateral sensorineural hearing loss in children". Ear Hear 7 (1): 3–13. PMID 3512353.
- Noble W, Gatehouse S (2004). "Interaural asymmetry of hearing loss, Speech, Spatial and Qualities of Hearing Scale (SSQ) disabilities, and handicap". International journal of audiology 43 (2): 100–14. PMID 15035562.
- Hol, M. K. S.; Kunst, S. J. W.; Snik, A. F. M.; Cremers, C. W. R. J. (2009). "Pilot study on the effectiveness of the conventional CROS, the transcranial CROS and the BAHA transcranial CROS in adults with unilateral inner ear deafness". European Archives of Oto-Rhino-Laryngology 267 (6): 889–896. doi:10.1007/s00405-009-1147-9. PMC 2857795. PMID 19904546.
- Popelka, G. (2010). "SoundBite Hearing System by Sonitus Medical: A New Approach to Single-Sided Deafness". Seminars in Hearing 31 (4): 393–409. doi:10.1055/s-0030-1268037.
- Stenfelt S (March 2005). "Bilateral fitting of BAHAs and BAHA fitted in unilateral deaf persons: acoustical aspects". Int J Audiol 44 (3): 178–89. PMID 15916119.
- Hol MK, Bosman AJ, Snik AF, Mylanus EA, Cremers CW (September 2005). "Bone-anchored hearing aids in unilateral inner ear deafness: an evaluation of audiometric and patient outcome measurements". Otol. Neurotol. 26 (5): 999–1006. PMID 16151349.
- Lieu, J. E. C. (2004). "Speech-Language and Educational Consequences of Unilateral Hearing Loss in Children". Archives of Otolaryngology - Head and Neck Surgery 130 (5): 524–530. doi:10.1001/archotol.130.5.524. PMID 15148171.
Mild and Unilateral Hearing Loss: Implications for Early Intervention
- Profound Unilateral Hearing Loss FAQ's and Flash Animation
- Unilateral Hearing Loss - Notes