Bilateral (two) versus unilateral (one) hearing aid(s) for bilateral hearing impairment in adults

Review question

Should adult patients with bilateral (two-sided) hearing loss be fitted with one or two hearing aids?

Background

Hearing loss can be present from birth or can come on in later life. The latter is called 'acquired' hearing loss and is common. Its incidence increases markedly with age. In most people, 'age-related' hearing loss is due to the loss of cells in the inner ear (so called 'sensorineural hearing loss') and affects both ears to the same degree. Hearing loss categorised as mild, moderate or severe is primarily managed with hearing aids. People with bilateral hearing loss may be offered one aid, fitted to one specific ear, or two aids fitted to both ears. There is uncertainty about the relative benefits to patients of these different strategies.

Study characteristics

We included four studies with a total of 209 patients, ranging in age from 23 to 85 and with more men than women. All the studies allowed the use of hearing aids for a total period of at least eight weeks before questions were asked about their preference for one or two aids. In all the studies the patients had bilateral hearing loss but there was considerable variation in what type of hearing loss they suffered from and how bad their hearing was.

Three of the studies were published before the mid-1990s and the fourth study was published in 2011. Therefore, only the most recent study used 'modern' hearing aids similar to those that are widely available in high-income countries. Of the four studies, two were conducted in the UK in National Health Service (NHS – public sector) patients. One of these looked at patients from primary care whose hearing loss had been picked up by a screening programme. The other looked at patients whose primary care practitioner thought they might benefit from hearing aids so had referred them to the local ENT department to get them. The other two studies were conducted in the United States: one study recruited only people on active military duty, or who had served in the military and had hearing loss due to being exposed to loud noises. About half of the people in the other study were ex-military.

Key results and quality of the evidence

Only one of the outcomes we thought was most important - patient preference - was reported in all studies. The percentage of patients who preferred two hearing aids to one varied between studies: this was 54% (51 out of 94), 39% (22 out of 56), 55% (16 out of 29) and 77% (23 out of 30), respectively. We did not combine the numbers from these four studies because it would not have been right to do so. We graded the quality of evidence for this outcome as very low on a scale that goes high – medium – low – very low. There was no information in the four studies on the other outcomes we were interested in.

Conclusions

This review identified only four studies comparing the use of one hearing aid with two. The studies were small and included people of widely varying ages. There was also considerable variation in the types of their deafness and in how deaf they were.

For the most part, the types of hearing aid evaluated would now be regarded, in high-income countries, as 'old technology', with only one study looking at 'modern' digital aids. However, we do not know if this is relevant or not. This review did not look at the differences between other 'old' and 'new' types of hearing aid.

We could not combine the numbers from the four studies. Overall, this fact and the very low quality of the evidence leads us to conclude that we do not know if patients have a preference for one aid or two. Similarly, we do not know if a patient's quality of life is better with one or two aids.

Authors' conclusions: 

This review identified only four studies comparing the use of one hearing aid with two. The studies were small and included participants of widely varying ages. There was also considerable variation in the types and degree of sensorineural hearing loss that the participants were experiencing.

For the most part, the types of hearing aid evaluated would now be regarded, in high-income settings, as 'old technology', with only one study looking at 'modern' digital aids. However, the relevance of this is uncertain, as this review did not evaluate the differences in outcomes between the different types of technology.

We were unable to pool data from the four studies and the very low quality of the evidence leads us to conclude that we do not know if people with hearing loss have a preference for one aid or two. Similarly, we do not know if hearing-specific health-related quality of life, or any of our other outcomes, are better with bilateral or unilateral aids.

Read the full abstract...
Background: 

Acquired hearing loss is common and its incidence increases markedly with age. In most people, 'age-related' hearing loss is sensorineural (due to the loss of cochlear hair cells) and bilateral, affecting both ears to the same degree. Hearing loss categorised as mild, moderate or severe is primarily managed with hearing aids. People with bilateral hearing loss may be offered one aid, fitted to one specific ear, or two aids fitted to both ears. There is uncertainty about the relative benefits to people with hearing loss of these different strategies.

Objectives: 

To assess the effects of bilateral versus unilateral hearing aids in adults with a bilateral hearing impairment.

Search strategy: 

The Cochrane ENT Information Specialist searched the ENT Trials Register; Cochrane Register of Studies Online; PubMed; Ovid Embase; CINAHL; Web of Science; ClinicalTrials.gov; ICTRP and additional sources for published and unpublished trials. The date of the search was 8 June 2017.

Selection criteria: 

Randomised controlled trials (RCTs) comparing the fitting of two versus one ear-level acoustic hearing aids in adults (over 18 years) with a bilateral hearing impairment, both ears being eligible for hearing aids.

Data collection and analysis: 

We used the standard methodological procedures expected by Cochrane. Our primary outcomes were patient preference for bilateral or unilateral aids, hearing-specific health-related quality of life and adverse effects (pain or discomfort in the ear, initiation or exacerbation of middle or outer ear infection). Secondary outcomes included: usage of hearing aids (as measured by, for example, data logging or battery consumption), generic health-related quality of life, listening ability and audiometric benefit measured as binaural loudness summation. We used GRADE to assess the quality of the evidence for each outcome; this is indicated in italics.

Main results: 

We included four cross-over RCTs with a total of 209 participants, ranging in age from 23 to 85 and with a preponderance of men. All the studies allowed the use of hearing aids for a total period of at least eight weeks before questions on preference were asked. All studies recruited patients with bilateral hearing loss but there was considerable variation in the types and degree of sensorineural hearing loss that the participants were experiencing.

Three of the studies were published before the mid-1990s whereas the fourth study was published in 2011. Therefore, only the most recent study used hearing aids incorporating technology comparable to that currently readily available in high-income settings. Of the four studies, two were conducted in the UK in National Health Service (NHS – public sector) patients: one recruited patients from primary care with hearing loss detected by a screening programme whereas the other recruited patients who had been referred by their primary care practitioner to an otolaryngology department for hearing aids. The other two studies were conducted in the United States: one study recruited only military personnel or veterans with noise-induced hearing loss whereas about half of the participants in the other study were veterans.

Only one primary outcome (patient preference) was reported in all studies. The percentage of patients who preferred bilateral hearing aids varied between studies: this was 54% (51 out of 94 participants), 39% (22 out of 56), 55% (16 out of 29) and 77% (23 out of 30), respectively. We have not combined the data from these four studies. The evidence for this outcome is of very low quality.

The other outcomes of interest were not reported in the included studies.

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