Audiology - Understanding how an asymmetrical sensorineural hearing loss affects you

This leaflet explains how an asymmetrical hearing loss may affect you and the options available to help improve your hearing. If you have any questions, please speak to your Audiologist.

How we hear:

The ear canal, eardrum, and inner ear convert the vibrational energy of sounds in our environment into electrical signals, these are then presented to the brain. The brain uses those electrical signals and processes them to give us the sensation we know as hearing.

When we have two good hearing ears, the brain will use all the information it receives to hear in a certain way (binaural hearing). This is different if we have one ear that is not hearing well (or not hearing at all) such as with an asymmetrical hearing loss.

• It is important to note that if a significant hearing loss has been present from an early age, then a person may not be able to adjust to sound amplification through hearing aids in later life

Four ways in which hearing with two ears (binaural hearing) is different from hearing with one ear (asymmetrical hearing loss):

1.    Hearing in Noise

• It is important to note that in noisy and low-volume environments, the brain needs to have signals from both ears to do its job effectively, this is called binaural hearing

An important role of the brain in our hearing is to selectively filter out the non-important sounds we do not want to hear, such as background noises like air conditioning and to select the sounds we do want to hear, such as speech.

It is essential to have two separate streams of hearing information from both ears for the brain to be able to produce selective hearing. Without this (such as having only one hearing ear), there is not enough information for the brain to do this function. Someone without this ability will have more difficulty hearing in even a small amount of background noise.

Similarly, someone with an asymmetrical hearing loss will require extra effort to listen in these situations, which can result in increased tiredness.

• It is important to note that even with normal two-ear hearing, it can be hard to understand a conversation when background noise levels increase

2.    Sound Localisation (directionality of a sound)

The brain uses the angle at which a sound arrives at our ears to localise the source of that sound. For example, if a sound comes from the right it will register in the right ear before the left ear. The brain uses these small differences in timing to identify where the sound has originated from. Without this input (such as having only one hearing ear) this ability is lost.

3.    Binaural Loudness Summation

A sound that is heard by two ears is registered louder in the brain than if it is only heard by one ear. This means that hearing in some situations with quieter speech is worse with one hearing ear compared to two hearing ears.

4.    The Head Shadow Effect

A sound that is presented to one ear is blocked by the head from reaching the other ear with the same loudness. This affects higher frequency sounds more, which is important for speech understanding.

Options to improve your hearing (adults with an asymmetrical hearing loss):

1.    CROS (Contralateral routing of sound)/BICROS (Bi-contralateral routing of sound) hearing aid systems

A CROS hearing aid system can be used with a severe hearing loss in one ear, and normal hearing in the other. It uses a hearing aid to detect the sounds on the side of the non-hearing ear and sends these sounds wirelessly to the good ear (which also wears a hearing aid). The sound signals go to the brain using only one hearing pathway, therefore, it will not give you the benefits of binaural hearing.

Example of how a CROS system works

BiCROS hearing aids work in the same way as CROS except they amplify sound from both sides and feed the sound into the better hearing ear. This is a good option if your good ear also has a hearing loss that requires amplification.

CROS/BICROS hearing aids are non-surgical options available for an asymmetrical hearing loss. It is usually a necessary requirement to have had a significant trial of this type of hearing system as part of a BAHS assessment for a single-sided sensorineural hearing loss.

2.    BAHS (bone anchored hearing solutions) with a surgical implant

A BAHS usually involves an implant in the skull which allows a hearing aid to be attached to the head and transmits sounds via vibrations to the cochlea. It works in a similar way to the CROS aid apart from only being implanted on the non-hearing side. It uses vibrations via the skull to the better hearing ear, these signals are then sent to the brain up that one pathway.

Some examples of BAHS

• It is important to note that a BAHS used for an asymmetrical hearing loss usually requires the cochlea function on the good ear to be around normal hearing levels

3.    What if you have tried everything and not found what you are looking for?

If you have tried all options or do not wish to try all options, then it is not unusual for a person with a single-sided hearing loss to decide they do not want any additional hearing device. If this is your situation, you may want to let the people around you know that you have a single-sided hearing loss. That way, they will understand why you don’t always hear what they are saying or hear sounds that they hear.
 
It is very important to be able to hear well with your better hearing ear. If there is a hearing loss on this side as well as the non-hearing side, using a hearing aid may improve your hearing.

• It is important to note that even with hearing devices fitted, it can still be challenging when you have hearing issues in one of your ears. There may be times when you cannot hear as well as you would like

In summary:

What can a BAHS or a CROS aid system offer to someone with an asymmetrical sensorineural hearing loss?

They can improve your overall hearing especially in quieter listening situations.

They can improve your sound awareness on the non-hearing side.

What can BAHS or CROS aid system NOT offer to someone with an asymmetrical sensorineural hearing loss?

They cannot improve binaural hearing such as localisation of sounds.

They do not usually give improved hearing in noisy or difficult listening situations. In some background noise situations using a hearing solution on the non-hearing side can actually make your hearing worse because you are hearing more background noise compared to if you were not wearing the hearing solution.