Describing the hearing loss

A unilateral hearing loss (UHL) affects one ear only. The child can hear normally in one ear and has some difficulty hearing with the other ear. There are different types, degrees and configurations of unilateral hearing loss and this will impact on how the hearing loss is managed.

Types of hearing loss

The type of hearing loss depends on the site of the problem in the ear which may be anywhere from the outer ear through to the middle ear, inner ear and the auditory nerve which carries the sound impulses through to the auditory cortex in the brain.

Conductive hearing loss
Hearing loss associated with outer or middle ear problems is known as conductive hearing loss. Problems such as wax build up, middle ear infection (otitis media) or deformity of the outer or middle ear structures prevent sound being conducted to the inner ear. Sound is softened, making hearing difficult. Conductive hearing losses can often be treated with either medication or surgery.

Sensorineural hearing loss
Sensorineural hearing loss results from dysfunction in the inner ear and/or the auditory nerve. Most sensorineural hearing loss is due to abnormalities in the hair cells in the cochlea. Causes of hair cell abnormality include certain genes as well as external causes such as damage from loud music or infections. The quantity (loudness) and quality (clarity) of sound is affected in sensorineural hearing loss. Sensorineural hearing loss is permanent and cannot be treated with surgery.

Mixed hearing loss
A mixed hearing loss occurs when the cause of the hearing loss is both sensorineural and conductive. For example, a child with microtia and atresia with subsequent conductive hearing loss may also have a sensorineural hearing loss.

Table: Describing hearing loss

Degrees of hearing loss

Hearing loss is described as mild, moderate, severe and profound. The degree of hearing loss depends on how loud sounds need to be before the ear detects them.

Although your child is able to hear normally on one side, sounds coming from the direction of the deaf side are softer when heard by the hearing ear. This is due to the ‘head shadow effect.’ The sound must pass through or around the head to be heard by the functioning ear and results in a drop in the intensity or loudness of the sound. The child may hear the sound but it will be softer.

There is a difference between an ‘audible’ sound and an ‘intelligible’ sound. A child may be able to hear that someone is talking (the sound is audible) but not be able to understand what exactly is being said (the sound is not intelligible). We have all had this experience in a noisy environment when we know someone is saying something to us but are unsure what they are actually saying. As adults, our experience may allow us to infer what is being said; we catch a few words and can therefore understand the gist of the conversation. Children cannot do this. They do not have the experience or mastery of the language to be able to pull the threads of the conversation together. Children need consistently intelligible speech to understand what is being said to them.

Parents often wonder what their child’s hearing loss sounds like. There are simulators available for bilateral hearing loss but not unilateral hearing loss. By blocking one ear with an ear plug or cotton wool for a day, you can get some understanding of good and difficult listening environments for people with UHL.

The information below gives some indication of the degrees of hearing loss. This does not reflect the impact on the child with UHL when listening with both ears.

• Mild hearing loss. The quietest sounds the child can hear on the side with the hearing loss are between 26 and 40dB. The affected side will not detect sounds below this level, such as a mosquito or rustling leaves.
   
• Moderate hearing loss. The quietest sounds your child can hear on the side with the hearing loss are between 41-60dB. The affected side will not detect sounds below this level, such as whispering or some conversations.
   
• Severe hearing loss. The child can hear sounds between 70 and 90dB. The affected side will not detect sounds below this level, such as most conversational speech, traffic noise and the vacuum cleaner. Sounds that are very loud to the hearing ear, will be very soft to the affected ear.
   
• Profound hearing loss. The child can only hear sounds louder than 90dB on the side with the hearing loss. Sounds that are very loud to the hearing ear, will be very soft or undetectable to the affected ear. This is also sometimes referred to as single-sided deafness (SSD).

Table: Decibel comparison chart
This chart provides some indication of environmental sounds and their possible intensity or loudness.

Hearing loss can also be…

• Flat loss – the hearing loss is similar across all frequencies. This is most common in conductive hearing loss due to ear canal atresia.
• Ski-slope hearing loss – the hearing loss gets gradually worse towards the higher frequencies. The audiogram looks like a ski-slope. This is the most common type of hearing loss. The child might have a mild loss in the low frequencies dropping to a severe loss in the high frequencies.
• Reverse slope hearing loss -the hearing loss is greatest at the low frequencies and gradually improves towards the high frequencies. The audiogram looks like the reverse of the ski-slope loss. The child might have a moderate loss in the low frequencies and near normal hearing at the high frequencies.
• Fluctuating hearing loss – the hearing loss changes; some days it is better than others. A fluctuating hearing loss is typically found with middle ear infections.
• Progressive hearing loss – the hearing loss gets worse over time.
• Sudden hearing loss – the hearing loss occurs suddenly. A sudden hearing loss requires immediate medical attention to find a cause and possible treatment.
• Congenital hearing loss – the child is born with the hearing loss.
• Acquired hearing loss – the child develops a hearing loss sometime after birth. This may occur after meningitis or cholesteatoma.
• Bilateral hearing loss – the child has a hearing loss in both ears.  A small percentage of children with a unilateral loss will develop a hearing loss in the other ear as well.

Your child’s hearing loss

The audiologist at Hearing Australia will record your child’s hearing on a graph known as an audiogram and will discuss your child’s audiogram with you. The audiogram will explain the type and degree of hearing loss and the frequencies affected by the hearing loss.  This will assist the audiologist to discuss the management of your child’s hearing loss with you.

Next: Understanding UHL – Finding a cause