The concept of deafness
The average hearing threshold at speech frequencies (0.5, 1, 2, 4KHz) is 26dB or more, which is considered to have hearing impairment, and those with hearing loss within 70dB are weighed as hearing, and those above 70dB are deaf, which are collectively referred to as deafness (deafness) in clinical practice.
Classification of deafness
According to WHO 1980 deafness grading standard, the average speech frequency pure tone hearing threshold is divided into 5 grades
Grading of hearing loss (according to 500 Hz, 1 kHz, 2 kHz, 4 kHz air-conduction average threshold)
Hearing grading
Mean threshold (dB)
Rough judgment
Effect on children’s speech development
Normal hearing.
10 to 25
-
Mild hearing loss.
26 to 40
Sensory difficulty in listening to soft speech
No problem with quiet environments
No
Moderate hearing loss.
41～55
Have difficulty communicating in general conversation
Especially in noisy environments
Moderate to severe hearing loss.
56 to 70
Can only hear close sounds or loud noises
Unsatisfactory language development
Severe hearing loss.
71 to 90
Can’t hear ordinary communication at all
Language does not develop naturally
Very severe hearing loss.
> 90
Can hear loud noises or feel sound vibrations
Classification of deafness can be divided into three categories according to the location and nature of the lesion.
(a) Conductive deafness (conductive deafness).
If the A-B gap is greater than 60 dB, it is possible that the hearing bone chain is defective or broken. Conductive deafness is a condition in which the conduction pathway of sound waves in the outer or middle ear is blocked and does not travel normally to the inner ear receptors.
There are many congenital and acquired obstructive and inflammatory lesions that can cause conductive deafness. Eustachian tube obstruction, middle ear effusion, tympanic membrane perforation, middle ear effusion, middle ear granulation, otosclerosis, and cholesteatoma formation can all affect the conduction system of the ear and lead to conductive deafness from various causes.
(ii) Sensorineural deafness.
The air and bone conduction curves show a consistent decrease, and generally the high frequency hearing loss is more severe, so the hearing curve is gradual or abrupt; the severe sensorineural deafness curve is island-shaped, and a few sensorineural deafness can also be dominated by low frequency hearing loss. The cochlear lesion is generally called sensorineural deafness, while the postcochlear lesion is called neurological deafness, but it is not easy to distinguish clinically, so it is collectively called sensorineural deafness. The common diseases include sudden deafness, auditory neuroma, Meniere’s disease, advanced otosclerosis, and other diseases that damage the inner ear or cochlear nerve.
(iii) Mixed deafness.
A combination of audiological features of both conductive and sensorineural deafness. However, there is a certain air-bone difference.