Hearing-aid (HA) users with insufficient HA may be better helped with a "Bimodal solution" when replacing the HA with a Cochlear implant (CI) to the poorer hearing ear and a HA to the better hearing ear.

This randomised controlled trial can show the benefit in terms of better speech perception of the bimodal solution with CI to the poorest hearing ear compared to binaural hearing aids.

It can clarify if HAs users with insufficient HAs benefit will benefit from the bimodal solution when adding a CI to the poorer hearing ear in terms of better speech perception.

It can report the degree of perceived hearing handicap in bimodal CI-users versus bilateral HA-users by hearing -specific patient reported outcome measures (PROM) questionnaires.

And it can contribute to a specific cochlear implant candidacy criterion related to the transition from HA treatment to the CI treatment.

The purpose of this study is to determine if bimodal treatment with a hearing aid to the better hearing ear and CI to the poorer hearing ear increases the ability to understand speech and improve quality of life compared to patients that are treated with hearing aids only.

The benefit of bimodal fittings compared to the best possible bilateral HA treatment will be evaluated.

Cochlear implants (CI) have been used to restore hearing in individuals with severe to profound sensorineural hearing loss. Normally, it is required that speech identification scores are below 50% in the ear considered for implantation and that the discrimination in the best-aided condition should be 60% or less. These criteria exclude many patients with asymmetrical hearing, as they have speech identification above 60% in the best-aided condition. It is necessary to investigate how patients with asymmetrical hearing can benefit from a cochlear implant in the poorer hearing ear compared to when bilaterally fitted with HAs. Furthermore, it is still unclear at which clinical relevant candidacy criterion the optimal transition from HA treatment to CI treatment in the bimodal solution occurs, as randomized studies comparing HA users and CI users do not exist. The purpose of this study is to provide clinicians with better evidence to determine if patients who benefit insufficiently from bilateral HA treatment and have a speech discrimination of the better hearing ear > 50% will benefit from a CI in the poorer hearing ear. Patients intended to include in the study will all be adults >18 years with hearing loss on both ears where cochlear implant will be considered as a treatment for the poorest hearing ear. All patients have used hearing aids on both ears for at least 1 year. The benefit of bimodal fittings compared to the best possible bilateral HA treatment is evaluated. Furthermore, it is investigated if this results in increased speech intelligibility and quality of life with a bimodal solution where a cochlear implant is used on the poorer hearing ear compared to either CI alone or bilateral hearing aids. 60 patients referred for cochlear implant at Odense University Hospital will receive new HAs that are fitted for one month. Then they will be randomized to either the intervention group with CI+HA (bimodal) or to the wait and see control group with continuous use of HA+HA (bilateral) for another three months. Participants will undergo stratified randomization depending on the hearing thresholds prior to CI surgery in the poorest hearing ear. To provide better evidence to determine if patients who benefit insufficiently from bilateral Hearing aid treatment and have a speech discrimination of the better hearing ear > 50% will benefit from a Cochlear implant in the poorer hearing ear.

Patients randomized to the intervention group CI+HA will undergo surgery as soon as possible after randomization. The control group that will use the hearing aids for an additional three months, will also be offered the bimodal solution with CI to the poorer hearing ear after total of four months with HA+HA.

Description of the cohort Inclusion criteria - Adults >18 years old. - Fluent in Danish, including reading and writing - Willing to participate in and to comply with all requirements of the protocol. - Post-lingual deafness and use one or two HAs. - Participants should have aidable hearing in the ear not considered for CI implantation - Self-reported HA use of at least eight hour per day for at least one year in both ears prior to evaluation for cochlear implantation in order to ensure, that both ears have received auditive stimulation prior to participation in the study. If possible, the validity of the self-reported hearing aid use will be checked in the HA-log by the audiology assistants. - Participants should have a PTA (0.5,1,2,4 kHz) > 40 dB HL in the ear considered for CI implantation and PTA≥40 and ≤ 70dB HL in the ear not considered for implantation. - A speech identification score

Ethics approval for the conduct of this study was obtained from the Ethics Committee Southern Denmark. 21st August 2020.

The trial will be conducted in compliance with this study protocol. All participants will undergo a process of informed consent and will be aware that participation is strictly voluntary.

Participants may withdraw from the study at any time. The project is approved by the Danish Data Protection Agency (file no. 20/22868) in Region South Denmark which is an independent authority that supervises compliance with the rules on protection of personal data. ("paraplyanmeldelse" in danish).

The study statistic analysis plan will be implemented as well.

Inclusion Criteria

• Adults >18 years old.
• Fluent in Danish, including reading and writing
• Acquired post-lingual deafness
• Use of bilateral HAs for at least one year prior to evaluation for cochlear implantation candidacy. This to ensure, that both ears have received auditive stimulation
• PTA > 40 dB HL in the ear considered for CI implantation and PTA≥40 and ≤ 70dB HL in the contralateral ear in best aided condition, in quiet and in noise and in free field.
• SIS <70% in best aided condition in the ear considered for CI implantation and SIS ≥30% and ≤70% in best aided condition in the contralateral ear, in quiet and in noise and in free field.

Exclusion Criteria

• Vestibular loss in the ear not considered for CI implantation
• Surgical issues interfering with the site of implantation or anatomical contraindications such as cochlear malformations, which will be determined using MRI or CT-scans.
• Auditory nerve lesions.
• Central auditory pathway pathologies.
• Otosclerosis.
• Single sided deafness (SSD).

The data sharing is described in a Data Management Plan. All Data will be anonymised.

It is available