Patterns of deafness
Types of hearing loss
Deafness or hearing loss can occur in one or both ears, can be permanent or temporary and is defined by which part of the ear is affected (type of loss) and by the level of the loss of hearing.
Conductive loss occurs in the outer and middle ear and some can be treated. Sensorineural hearing loss, known as nerve deafness, occurs in the inner ear usually in the cochlea or beyond in the auditory nerve. This is a permanent loss.
Hearing tests are done for each ear by measuring responses to a pure tone signal providing a pattern of the hearing loss, called an audiogram, across the frequencies of human hearing, targeting the areas most important for access to speech. These responses, measured in decibels, are then averaged across 5 speech frequencies and described in more general terms. The British Society of Audiology (BSA) describes hearing threshold levels for each ear by using four bands of hearing loss known as audiometric descriptors. Found in section 9 of ‘Pure-tone air-conduction and bone conduction threshold audiometry with and without masking’
Descriptor average hearing threshold levels (dB HL)
Mild hearing loss 20-40
Moderate hearing loss 41-70
Severe hearing loss 71-95
Profound hearing loss In excess of 95
Where there is a bilateral loss (in both ears) the descriptor for the better ear is used.
However this is a clinical measurement and is not always a reliable indicator of the ability to access sound and communicate in many everyday contexts. BSA says, ‘….they shall not be used as the sole determinant for the provision of hearing support.’
The audiometric descriptor does not convey the impact of a hearing loss from birth which can cause significant difficulty for developing language and communication and hence learning and social interaction.
Impact of hearing loss
The type of hearing loss is significant as is the time of its onset. Many factors impact a child’s language and learning development and there are a variety of education outcomes in children and young people regardless of the level of hearing loss.
As a result of newborn hearing screening in the UK hearing loss is likely to be diagnosed well before any autism. If a baby fails the hearing screening further diagnostic tests within an audiology department take place.
For details of each of the tests see http://www.ndcs.org.uk/family_support/childhood_deafness/hearing_tests/newborn_hearing.html
Auditory brainstem response testing provides information regarding auditory function and hearing sensitivity.
It is often necessary to consider the results in conjunction with further behavioural audiometry whenever possible so that an accurate diagnosis of functional hearing is possible. Diagnostic testing for deafness may require some degree of co-operation and this can present challenges when autism is present but unknown.
There are cases of late onset deafness and progressive hearing loss which may not be detected at the time of newborn hearing screening. One has always to be alert to this possibility and especially when diagnosing Autism per se as indicators for both are similar. eg lack of response to sound, lack of eye contact, poor communicative intent, no shared attention.
In the UK a diagnosis of deafness, regardless of degree of hearing loss, is usually followed by a referral to the local Sensory Support Service. Criteria within the Local Offer of that Authority will determine the support package for the deafness needs of the child
