What one deaf ear costs
Single-sided deafness means a severe or profound loss in one ear with normal or near-normal hearing in the other. In quiet, one good ear copes. The difficulty appears where hearing is hardest, and a test of the good ear does not show it: hearing is more than an audiogram.
The head shadow. The head blocks high-frequency sound, so a voice on the deaf side reaches the hearing ear weakened and with less consonant detail. In noise, the head shadow alone can cost up to 6–7 dB of signal-to-noise ratio, a large difference for understanding speech.
Direction. Locating sound depends on comparing timing and loudness at the two ears. With one ear, that comparison is impossible: people turn the wrong way, cannot find a ringing phone, and feel less safe in traffic (see spatial hearing).
Noise. Two ears together suppress noise coming from a different direction from the voice you want to follow. With one ear, a busy restaurant or a meeting becomes much harder (see hearing in noise and binaural hearing).
Effort. Many people are exhausted after an evening out even though they followed most of the conversation. This listening effort is real, and often the complaint that matters most.
Causes, briefly
Causes in adults include a sudden sensorineural hearing loss, often without an identifiable reason; a tumour on the balance and hearing nerve (vestibular schwannoma) or its treatment; Ménière’s disease; head injury; inner-ear infection, including after meningitis or mumps; and, rarely, a complication of ear surgery. A severe or total inner-ear loss after stapedotomy, for example, occurs in about 0.5–1% of first operations. Some people are born with one deaf ear.
The cause matters. A cochlear implant needs a working hearing nerve, so an MRI scan, which also excludes a tumour, is part of the assessment.
If the loss is new, it is urgent. Hearing that drops over hours or days in one ear should be seen the same day; treatment is more effective when started early (see sensorineural hearing loss). The same applies after ear surgery: a sudden drop in hearing, or severe spinning vertigo, needs same-day care. Device decisions come later, once the hearing has stopped changing.
The four options
No device. A legitimate choice, helped by practical tactics such as sitting with the good ear towards the conversation. Protecting the hearing ear from noise matters more than ever, because it is now the only one.
CROS hearing aid (contralateral routing of signals). A microphone worn on the deaf ear sends sound wirelessly to a receiver on the hearing ear. No surgery. It overcomes the head shadow for sound from the deaf side, but everything still arrives in one ear, so it cannot give direction. When the better ear also has some loss, the receiver can amplify for that ear too (a BiCROS).
Bone-conduction device. A sound processor on the deaf side vibrates the skull, and the vibration reaches the hearing inner ear on the other side. It can be tried on a headband or an adhesive pad; long-term use usually means a small operation to place an implant in the bone behind the ear. Like CROS, it reroutes sound to the hearing ear; it does not make the deaf ear hear.
Cochlear implant. An electrode in the deaf ear’s cochlea stimulates the hearing nerve directly. It is the only option that gives the brain a signal from the deaf side, and so the only one that can bring back part of what two ears do together. It needs an operation under general anaesthesia, activation some weeks later and a period of rehabilitation; the implant’s sound at first is unfamiliar and becomes more natural with use.
What the CINGLE trial found
Before the trial, a systematic review by the author’s Utrecht group found no clear benefit of CROS aids or bone-conduction devices for hearing in noise or localisation, and no high-quality study comparing all the options. CINGLE, a randomised trial run by the same group, was designed to that gap: a cochlear implant against a bone-conduction device and a contralateral-routing hearing aid, with economic evaluation in the protocol. The implant was the only option that restored objective localisation and produced the largest reduction in tinnitus.
At two years, people with an implant understood speech in noise better than the other groups, located sounds more accurately, and rated their own hearing higher. The authors concluded that people with single-sided deafness can partially regain the advantages of two ears. Hearing does not become normal.
CROS aids and bone-conduction devices had a double edge. With speech on the deaf side, both helped. With noise on the deaf side, both made hearing worse than having no device, because they deliver that noise to the good ear. After trying both on a trial basis, about three in ten people chose to have no device at all.
CINGLE: design and numbers
Single-centre randomised trial at UMC Utrecht. Inclusion: adults, pure-tone average (0.5–4 kHz) ≥70 dB HL in the poor ear and ≤30 dB HL in the better ear, deafness of 3 months to 10 years (median 1.8 years). 120 patients were randomised to CI or to trial periods with a headband BCD and a CROS in either order, after which they chose an implanted BCD, CROS or nothing; 113 started follow-up (CI 28, BCD 25, CROS 34, none 26). Only the CI allocation was randomised, so comparisons between the BCD, CROS and no-treatment groups are less protected from selection. At 24 months, with noise to the poor ear, the CI group's speech reception threshold in noise was 4.7 dB better than BCD and 5.3 dB better than CROS. Against no treatment, BCD and CROS gained about 4 dB with speech to the poor ear and lost 4.0–4.6 dB with noise to the poor ear. Median THI fell by 23 points with CI. A meta-analysis of 36 non-randomised studies (796 adults) found localisation error reduced by about 25° and THI by about 30 points after implantation.
Tinnitus
Tinnitus in the deaf ear is common and, for some people, the main complaint. In CINGLE, tinnitus burden fell most in the implant group, and the change was already visible at three months and stable to two years. A smaller reduction was seen with bone-conduction devices. Reviews of other implant studies show the same direction. An implant is not a guaranteed cure: some people notice little change, and the effect for one person cannot be predicted.
Who benefits from which
- CROS suits someone who mainly wants to hear people on the deaf side, such as a colleague at the next desk, without surgery, and who does not mind wearing something on the good ear.
- A bone-conduction device does a similar job without anything in the hearing ear. It can suit people who find an earpiece in the good ear uncomfortable. The headband trial shows what it can do before any operation.
- A cochlear implant suits adults whose hearing nerve is intact, who want direction and hearing in noise back, or whose tinnitus is troublesome, and who accept an operation and months of practice.
- No device suits people who are coping, or who found no device worth wearing.
Time since deafness. The brain reorganises around the hearing ear. A systematic review found poorer implant speech scores with longer deafness, but too much uncertainty to support a fixed limit such as five or ten years. CINGLE included people deaf for up to ten years. An implant is best considered early; a long duration calls for careful assessment rather than an automatic no.
This page is about adults. In children, the questions and the timing are different, and decisions are made with a paediatric team.
Costs and practicalities
CROS. Costs similar to a pair of hearing aids, replaced every few years; daily wear, charging, and a device in the good ear.
Bone-conduction device. The trial is cheap; the implanted version means a short operation and a processor replaced over the years. Devices with a post through the skin need daily skin care and can cause skin reactions; those held by a magnet avoid the post but may limit MRI scanning.
Cochlear implant. The most expensive option at the start: operation, implant, months of programming and rehabilitation, and processor upgrades for life. Reimbursement for single-sided deafness depends on the country and the insurer. A French multicentre trial, which also included asymmetric hearing loss, found the cost per quality-adjusted life year very high over the first six months; using a long-term model, the authors judged the implant good value once benefit was counted over about 20 years, or within 10 years for people with severe tinnitus. Implants also bring MRI restrictions to check before any scan.
None of the options involves operating on the hearing ear. Hearing rehabilitation places these devices among the others; hearing preservation explains why the remaining ear deserves protection.
Sources
- Peters JPM, Smit AL, Stegeman I, Grolman W. Review: Bone conduction devices and contralateral routing of sound systems in single-sided deafness. Laryngoscope. 2015;125(1):218-226. PubMed
- Peters JPM, van Heteren JAA, Wendrich AW, et al. Short-term outcomes of cochlear implantation for single-sided deafness compared to bone conduction devices and contralateral routing of sound hearing aids — results of a randomised controlled trial (CINGLE-trial). PLoS One. 2021;16(10):e0257447. PubMed
- Wendrich AW, Assouly KKS, van Heteren JAA, et al. Tinnitus reduction in patients with single-sided deafness: the effect of cochlear implantation, bone conduction devices, and contralateral routing of sound hearing aids investigated in a randomized controlled trial. Front Neurol. 2024;15:1428106. PubMed
- van Heteren JAA, van Oorschot HD, Wendrich AW, et al. Sound localization in single-sided deafness; outcomes of a randomized controlled trial on the comparison between cochlear implantation, bone conduction devices, and contralateral routing of signals hearing aids. Trends Hear. 2024;28:23312165241287092. PubMed
- van Heteren JAA, Wendrich AW, Peters JPM, et al. Speech perception in noise after cochlear implantation for single-sided deafness: a randomized clinical trial. JAMA Otolaryngol Head Neck Surg. 2025;151(3):211-219. PubMed
- Daher GS, Kocharyan A, Dillon MT, Carlson ML. Cochlear implantation outcomes in adults with single-sided deafness: a systematic review and meta-analysis. Otol Neurotol. 2023;44(4):297-309. PubMed
- Cohen SM, Svirsky MA. Duration of unilateral auditory deprivation is associated with reduced speech perception after cochlear implantation: a single-sided deafness study. Cochlear Implants Int. 2019;20(2):51-56. PubMed
- Marx M, Mounié M, Mosnier I, et al. Cost-utility of cochlear implantation in single-sided deafness and asymmetric hearing loss: results of a randomized controlled trial. Eur J Health Econ. 2025;26(5):735-744. PubMed
Common questions
I am deaf in one ear. Do I need to do anything about it?
Not necessarily. Many people manage well with practical tactics: sitting with the good ear towards the speaker, choosing quieter places, and asking others to stand on the hearing side. Treatment is worth considering if noise, finding where sounds come from, tiredness after social events or tinnitus are limiting daily life. If the loss is new, however, it needs medical assessment the same day, before any thought of devices.
Is a CROS hearing aid or a bone-anchored hearing aid better for single-sided deafness?
They do the same basic job: they pick up sound on the deaf side and deliver it to the hearing ear, a CROS aid by radio and a bone-conduction device through the skull. In the CINGLE trial neither gave the brain direction back, and both made hearing worse when noise came from the deaf side. Comfort and sound quality usually decide, so trying both before choosing is sensible.
Can a cochlear implant help if I am deaf in only one ear?
Yes, in suitable adults. It is the only option that sends a signal from the deaf ear itself. In a randomised trial it gave better hearing in noise, better localisation and the largest drop in tinnitus at two years compared with a CROS aid or a bone-conduction device. It needs an operation, a working hearing nerve and months of practice, and the sound at first is unfamiliar.
Will a cochlear implant stop the tinnitus in my deaf ear?
It often reduces it, and sometimes it disappears, but it cannot be promised. In the CINGLE trial, tinnitus burden fell most in the implant group, and the change was already visible at three months. Reviews of other studies show the same pattern. Tinnitus that does not change, or rarely becomes worse, remains possible and should be discussed before surgery.
Is it too late for a cochlear implant if I have been deaf in one ear for many years?
Not automatically. Results tend to be poorer the longer an ear has been deaf, but the evidence is too uncertain to support a fixed limit such as five or ten years. The CINGLE trial included people deaf for up to ten years. After a longer time, the decision rests more on the individual assessment and on what the person most wants to improve.
This page provides general educational information. It cannot replace an individual assessment, which depends on a full history, examination, audiometry and, where relevant, imaging. If you have sudden hearing loss, severe pain, facial weakness, severe dizziness or discharge with fever, seek medical care promptly.