Assessment of Hearing

Yapa WijeratneFaculty of MedicineUniversity of Peradeniya

• Loud sounds and hearing loss• Intense sounds can cause1. hair cell death2. nerve fiber degeneration

• What is Hearing Testing?• Hearing testing is a means of evaluating an individual's overall hearing

function. • Hearing can be impaired due to lesions in the external ear canal, the middle

ear, or the inner ear. • The purpose of hearing testing is to evaluate hearing function and, if it is

impaired, to attempt to localize the site of lesion.

Types of deafness/ hearing loss

1. Sensorineural (SN) hearing loss/ Nerve Deafness – impairment of the cochlea or impairment of the auditory nerve

2. Conductive hearing loss/ Conduction Deafness– impairment of the physical structures that conduct the sound into the cochlea

3. Mixed hearing loss

1. Sensorineural (SN) hearing loss

• destruction of the cochlear or the auditory nerve

• the person becomes permanently deaf

• It results from lesions of the cochlea (sensory type) or • VIIIth nerve and its central connections (neural type). • The term retrocochlear is used when hearing loss is due to lesions of

VIIIth nerve, and • central deafness, when it is due to lesions of central auditory

connections.

2. Conductive hearing loss

• destruction of tympanum-ossicular system

• sound can still be heard via bone (ossicular) conduction

Conductive hearing loss• It is caused by any disease process interfering with the conduction of

sound from the external ear to the stapediovestibular joint. • Thus the cause may lie in

3. Mixed hearing loss

• In this type, elements of both conductive and sensorineural deafness are present in the same ear. • There is air-bone gap indicating conductive element, and impairment

of bone conduction indicating sensorineural loss. • Mixed hearing loss is seen in some cases of otosclerosis and chronic

suppurative otitis media.

While assessing the auditory function it is important to find out:

A. Type of hearing loss A. (conductive, sensorineural or mixed).

B. Degree of hearing loss A. (mild, moderate, moderately severe, severe, profound or total).

C. Site of lesion. A. If conductive, the lesion may be at external ear, tympanic

membrane, middle ear, ossicles or eustachian tube. Clinical examination and tympanometry can be helpful to find the site of such lesions.

B. If sensorineural, find out whether the lesion is cochlear, retrocochlear or central. Special tests of hearing will be required to differentiate these types.

D. Cause of hearing loss. A. The cause may be congenital, traumatic, infective, neoplastic,

degenerative, metabolic, ototoxic, vascular or autoimmune process. Detailed history and laboratory investigations are required.

Bedside Testing of Hearing

• Three different sized tuning forks. The higher pitched forks (such as the 256 or 512 Hz fork) are more appropriate for hearing testing.

Rinne’s Test

• The single most common office test is a tuning fork test called the Rinne, named after Adolf Rinne, who described this test in 1855. • In the Rinne test, a comparison is made between hearing elicited by

placing the base of a tuning fork applied to the mastoid process (bone), and then after the sound is no longer appreciated, the vibrating top is placed one inch from the external ear canal (air).

• Normal findings• The sound is louder at the ear, that is, air conduction is better than bone conduction. • Record this as AC > BC; this is normal (Rinne positive).• Abnormal findings• If the sound is louder on the mastoid process, bone conduction is better than air

conduction. • Record this as BC > AC (Rinne negative). • This applies in conductive deafness• A false-negative Rinne’s test may occur if hearing is very poor on one side. • Then, the sound travelling through the air is not perceived but, when the tuning fork

is placed on the mastoid process of the ‘poor’ ear, the sound is conducted through the skull and heard in the ‘good’ ear.• In a mild conductive deafness, the Weber test is abnormal (lateralised) before the

Rinne.

Normal Hears vibration in air after bone conduction is over

Conduction deafness of one

ear

Vibration in air is not heard after bone conduction is over

Partial nerve deafness of one

ear

Vibration in air is heard after bone conduction is over

Complete nerve deaf-ness of one

ear

Vibration is not heard on the affected side

Weber’s Test

• In the Weber test, a 512 Hz tuning fork is placed on the patient's forehead. • If the sound lateralizes (is louder on one side than the other), the

patient may have either an ipsilateral conductive hearing loss or a contralateral sensorineural hearing loss.

WeberVertex

• Normal findings• The noise is heard in the middle or equally in both ears.• Abnormal findings• The noise is louder in an ear with conductive deafness (test on yourself by

putting a finger in your outer canal to block out surrounding noise). • In unilateral sensorineural deafness the sound is heard better in the

better-hearing ear. • In symmetrical hearing loss it is heard in the middle.

Normal Hears equally on both sides

Conduction deafness of one ear

Sound louder in the diseased ear

Partial nerve deafness of one ear

Sound louder in the normal ear

Complete nerve deaf-ness of one ear

Sound heard only in the normal ear

Tuning fork tests and their interpretation

Test Normal Conductive deafness SN deafness

Rinne AC > BC (Rinne positive) BC > AC (Rinne negative) AC > BC

Weber Not lateralised Lateralised to poorer ear Lateralised to better ear

Audiometry• Audiometry is the term used to describe formal measurement of hearing.

The measurement is usually performed using an "audiometer" by an "audiologist". • In audiometry, hearing is measured at frequencies varying from low pitches

(125 Hz) to high pitches (8000 Hz). • Produces pure tones of different frequencies. Is used to determine the

nature of hearing disabilities.• The audiometer is calibrated so that zero intensity level of sound at each

frequency is the loudness that can barely be heard by the normal person (0 db).• Audiometry provides a more precise measurement of hearing.

• Air conduction is tested by having the subject wear earphones attached to the audiometer.• Pure tones of controlled intensity are delivered to one ear at a time. • The subject is asked to raise a hand, press a button, or otherwise

indicate when he/she hears a sound. • An attachment called a bone oscillator is placed against the bone

behind each ear (mastoid bone) to test bone conduction.

Audiogram

• The minimum intensity (volume) required to hear each tone is graphed, and the results are called an audiogram. • The hearing level is quantified relative to "normal" hearing in decibels

(DB), with higher numbers of DB indicating worse hearing.• The DB score is not really percent loss, but nevertheless 100 dB

hearing loss is nearly equivalent to complete deafness for that particular frequency. • A score of 0 is normal. It is possible to have scores less than 0, which

indicate better than average hearing.

Audiogram for a Patient with Normal Hearing

• When there is a hearing loss, the next step is to try and determine whether the loss is caused by a sensory problem (sensorineural hearing loss) or a mechanical problem (conductive hearing loss). • This distinction is made by using a bone vibrator, which bypasses the

mechanical parts of the middle ear. • If hearing is better using bone than air, this suggests a conductive

hearing loss.

Interpretation of audiogram

• When air conduction tests show a hearing loss, but there is no loss identified with bone conduction tests, there may be a conductive loss.• When both air and bone conduction results show hearing loss at the

same level, the loss is considered sensorineural.• If different degrees of hearing loss are found via air and bone

conduction testing, the loss is mixed.

Audiogram of right ear showing conductive hearing loss with Air-Bone gap

Sensorineural hearing loss with no A-B gap

Early case of noise-induced hearing loss (NIHL). Note dip at 4000 Hz.

Mixed hearing loss

Conductive hearing loss Sensorineural hearing loss (SNHL)

1. Negative Rinne test, i.e. BC > AC. 2. Weber lateralised to poorer ear. 3. Low frequencies affected more. 4. Audiometry shows bone conduction better than air conduction with air-bone gap. Greater the air-bone gap, more is the conductive loss. 5. Loss is not more than 60 dB.

1. A positive Rinne test, i.e. air AC > BC.2. Weber lateralised to better ear.3. More often involving high frequencies.4. No gap between air and bone conduction curve on audiometry.5. Loss may exceed 60 dB.

Hearing tests in children

• These ages are important to select the appropriate test to assess patients with suspected hearing abnormalities.

Test Minimum age

Evoked otoacoustic emission (EOAE)

Newborn

Auditory brainstem response (ABR) audiometryDistraction testing 7–9 months of age

Visual reinforcement audiometry

10 and 18 monthscan be used between the age of 6 months and 3 years

Performance and speech discrimination testing

18 months to 4 years

Audiometry from 4 years old

Test your knowledge

1. What is the investigation shown in this picture?2. Identify the tracing3. Comment on the findings

OSCE STATION-1

1. What is the investigation shown in this picture?• Pure tone audiometry (PTA)

2. Identify the tracing• Audiogram

3. Comment on the findings• Normal intensity of hearing is between -10 to 20 dB.• In right ear• Air conduction & bone conduction both are reduced in high frequencies.• So sensorineural hearing loss of the right ear.• In left ear• Bone conduction is normal but air conduction is low.• Therefore conductive hearing loss is found in left ear.

Comment on the hearing in following cases.

OSCE STATION-2

Comment on the hearing in following cases.

• Positive Rinne in each ear & Weber test referred equally to each ear indicating symmetrical hearing in both ears with normal hearing or bilateral equally reduced sensorineural hearing loss.

OSCE STATION-2

OSCE STATION-3

• Positive Rinne test on both sides & the Weber test is referred to the left ear indicating sensorineural deafness in the right ear.

OSCE STATION-3

OSCE STATION-4

• Rinne test is negative on the right, positive on the left & the Weber test is referred to the right ear indicating conductive deafness in the right ear.

OSCE STATION-4

T/F MCQ

1. Tuning folk tests are best performed with the 128 Hz tuning folk.2. Non lateralized Weber test always indicates normal hearing.3. Negative Rinne right ear & Weber test lateralized to right ear

indicates conductive hearing loss of right ear. 4. In case of ruptured tympanic membrane, BC > AC.5. Audiometry can be used to reliably assess the hearing of 6 year old

child.

T/F MCQ

1. Tuning folk tests are best performed with the 128 Hz tuning folk.2. Non lateralized Weber test always indicates normal hearing.3. Negative Rinne right ear & Weber test lateralized to right ear indicates

conductive hearing loss of right ear. 4. In case of ruptured tympanic membrane, BC > AC.5. Audiometry can be used to reliably assess the hearing of 6 year old child.

• Answers• FFTTT