Hearing loss and tests

In this article, we will learn about the definition of deafness or hearing loss. We will discuss types of hearing loss, their causes, and much more.

Table of contents:

1. Introduction

2. Types

3. Causes

4. Hearing tests

5. Treatment

Hearing impairment is the inability to hear or the reduction in the hearing capacity of an average person.

Sound waves reach the cochlea in two ways:

1. Through air in the external and middle ear ( air conduction). Sound waves produce movements in the tympanic membrane, which initiates movements in the ossicles present in the middle ear. Movements in the ossicles of the middle ear cause vibration in the basilar membrane.

2.Through skull bones( bony conduction.) Sound waves produce vibrations in the skull bones, including the cochlea, which triggers vibrations in the basilar membrane.

Types:

1. Conductive deafness

2. Neural deafness or sensorineural deafness, and

3. Mixed deafness.

In conductive deafness, there are defects or impairment of functions in the conduction of sound waves. It usually causes incomplete deafness.

In Neural deafness, there may be defects in the conversion of sound waves into action potential and its transmission through the auditory pathway. Neural deafness is also known as ‘central deafness.’ It causes complete deafness.

Mixed deafness is due to causes of conductive and neural deafness.

Common causes of conductive deafness defect in :

1. External ear block in external auditory meatus by wax, foreign body, atresia, or tumor of the external auditory canal.

2. Middle ear:

• Tympanic membrane perforation of the tympanic membrane, thickening of the tympanic membrane.
• Infection of middle ear-otitis media.
• Ossicles- impaired movements in ossicles due to infection.
• Otosclerosis.
• Eustachian tube obstruction is usually due to infections.

Common causes of Neural deafness:

1. structure of cochlea

• Degenerative changes due to ageing-senile degeneration
• Toxic degeneration of hair cells -drugs,
• Prolonged exposure to loud sounds.

2. Tumors in the neural pathway or adjacent area compress the pathway.

3. inflammation of the labyrinth- labyrinthitis.

4. Miniere’s disease

5. Trauma of skull.

6. Genetic mutations in some proteins like Connexin 26, Myosin-VI, Myosin-VIIa, Sulfate transport protein, and Barttin.

Genetic mutations will cause mixed deafness.

Hearing tests:

The subject sits on a comfortable chair. The examiner explains the procedure to the subject.

1. Examination of external ears

It starts by examining the external ears, the pinna, and the external auditory meatus.

The pinna is examined for its structure and evidence of any physical abnormalities.

The examiner examines the external auditory meatus. The examiner stands in such a way that he can observe inside the external auditory meatus. The pinna is pulled gently upward and backward to straighten the external auditory meatus.

Points of observation: wax, foreign bodies, and any growth.

Now, an ear speculum is introduced gently in the external auditory meatus. A beam of light is thrown into the ear speculum to visualize the tympanic membrane. The tympanic membrane becomes visible and examined in different directions and positions.

The tympanic membrane is recognized by its oval shape, concavity pointing medially, cone of light, and glistening, shining look.

The center of the tympanic membrane appears depressed-this is the umbo.

The upper part of the tympanic membrane is pinkish and appears flaccid, while the lower and significant part appears blue and tense.

A cone of light-cone-shaped light reflection appears in the antero-inferior quadrant of the tympanic membrane.

If the light reflex is absent or dull- it indicates infection of the middle ear or secretion in the middle ear. It also shows an infection of the external ear.

2. Whisper test

Generally, a person can hear a whisper from a distance of 12-15 inches.

This test is performed in a quiet room. One ear of the subject is occluded, and the examiner is near his other ear. The examiner whispers some simple questions, for example, his name, from a distance of about 15 inches. If the subject hears, he will answer. It indicates that air conduction of that ear is normal.

The procedure is conducted for another ear.

3. Watch test

The subject is asked to close his eyes, occlude one ear, and raise his hand when he hears the watch tick.

The examiner moved a watch from three feet to his open ear and noted the distance when the subject reported hearing the sound.

The procedure is repeated with another ear.

Usually, a healthy subject will hear a tick of a watch from a distance of three feet.

3. Tuning fork tests: Rinne test (Rinnie’s test), Weber test, and Schwabach test. The tests are named after scientists who discovered them.

A few main points

1. You may use a tuning fork of 128/256 or 512-hertz vibrations.

2. Air conduction is better than bone conduction.

Sound is conducted through an ossicular system to the inner ear-cochlear apparatus.

Bone conduction is the conduction of sound through the skull bones.

Aims -1. To know whether hearing impairment /deafness is due to air or bony conduction.

2. To determine whether the hearing impairment is due to conductive or neural defects.

Rinne test:

The examiner explains the procedure to the subject, and the subject is asked to raise one finger as soon as he hears the vibrating sound of the tuning fork and raise two fingers when he cannot hear that.

A tuning fork is made to vibrate by stroking it on your thenar eminence, and the base of the tuning fork is kept on the mastoid process. [The mastoid process is the bony part behind the pinna.]The subject hears the vibrating sound of the tuning fork and raises one finger. He hears the sound by bone conduction.

After that, he raises his two fingers, indicating he cannot hear the sound. Then, immediately, the vibrating tuning fork is placed near his external auditory meatus. He raises one finger to inform that he can listen to the sound. Now, he hears through air conduction.

In this case, air conduction is better than bone conduction, so his hearing ability is average.

Rinne positive means air conduction is better than bone conduction. Rinne’s positive test is normal.

Rinne negative means bone conduction is better than air conduction, indicating that the subject suffers from air conduction deafness.

In this condition, the subject cannot hear the sound when the vibrating tuning fork is placed near his ear after he fails to hear through bone conduction. It means bony conduction is better than air conduction.

One may observe three phenomena:

1. Normal: air conduction is better than bone conduction.

2. Conduction deafness: bone conduction is better than air

conduction.

3. Nerve deafness: no sound is heard, and bone and air conductions are absent.

Weber test:

In this test, a vibrating tuning fork base is placed at the center of the forehead or on the vortex of the subject’s skull with caution.

He is asked to indicate whether he hears the sound equally from both ears or better from one ear.

1. Normally, he hears equally in both ears.

2. In conduction deafness, the subject will hear it louder in the diseased ear.

3. In nerve deafness, the subject hears the sound louder in the normal ear.

This test determines the type of deafness, whether bone conduction deafness or air conduction deafness.

If one ear suffers from nerve deafness, the subject hears the sound better from the opposite ear.

If one suffers from conduction deafness, he will hear better in the diseased ear.

Schwabach test:

In this test, we compare the hearing capacity of the subject with that of the examiner, assuming that the examiner is average.

In this test, a vibrating tuning fork base is placed on the mastoid process of the subject. When the subject cannot hear the sound of the vibrating tuning fork, the examiner immediately puts the base of the fork on his mastoid process.

If the examiner hears the sound, the subject suffers from nerve deafness.

If the examiner cannot hear the sound, the subject suffers from bone conduction deafness.

Audiometry:

Audiometry is the process of objective and subjective tests for hearing impairment.

Audiometry is performed by an electronic equipment called an audiometer, and the record is known as an audiogram. A specialist performs this test.

There are two main types:

Pure tone and speech Audiometry.

Brain stem auditory evoked responses [BAERs]:

Auditory stimulation causes action potential in the auditory pathway, recorded by special electronic equipment in waveforms; this is BAER.

The waves are named I to V depending on the site of their origin.

Wave I from the cochlear nerve

Wave II from the cochlear nerve,

Wave III from the superior olivary nucleus

Wave IV originates from the nucleus of the lateral lemniscus

Wave V arises from the inferior colliculus.

Interference:

The absence or reduced amplitude of waves indicates a lesion of that area and helps in the localization of tumors in the auditory pathways.

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