Hearing Loss: What You Need to Know

1. How Does Hearing Occur?

• Humans perceive sound through two pathways: air conduction and bone conduction, with air conduction playing the primary role.
• Sound is received by the outer ear, causing the tympanic membrane to vibrate. These vibrations are transmitted through the ossicular chain into the cochlea. The cochlea converts the received signals into electrical impulses, which are then transmitted through the auditory nerve to the brain.
• The brain analyzes the sounds received from both ears, allowing humans to perceive and understand sound comprehensively.
• Therefore, hearing is a continuous and complex process involving multiple organs. Damage to any one of these structures can result in hearing loss.
• Sound is assessed by intensity (loudness), measured in decibels (dB), and pitch (frequency), measured in hertz (Hz).
• The range of frequencies that humans can hear is approximately 20 Hz to 20,000 Hz.
• Diagram illustrating the intensity and frequency levels of sounds encountered in everyday life.

2. How Many Types of Hearing Loss Are There?

There are three types of hearing loss:

• Conductive hearing loss: caused by damage to the outer or middle ear.
• Sensorineural hearing loss: caused by damage to the cochlea or retrocochlear structures.
• Mixed hearing loss: a combination of conductive and sensorineural hearing loss.

2.1. Degrees of Hearing Loss

• Normal hearing: hearing threshold ≤ 20 dB.
• Mild hearing loss: hearing threshold from 20–40 dB.
• Moderate hearing loss: hearing threshold above 40–70 dB.
• Severe hearing loss: hearing threshold above 70–90 dB.
• Profound hearing loss: hearing threshold > 90 dB.

3. What Causes Hearing Loss?

Hearing loss may develop gradually or occur suddenly (sudden hearing loss). Sudden hearing loss is considered a medical emergency and therefore requires diagnosis and treatment as early as possible.

3.1. Conductive Hearing Loss

Possible causes include earwax impaction; congenital or acquired narrowing or atresia of the external auditory canal; tympanic membrane perforation; otitis media with effusion; mastoiditis caused by infection or cholesteatoma; and disorders of the ossicular chain, such as otosclerosis or traumatic ossicular dislocation.

3.2. Sensorineural Hearing Loss

• Congenital hearing loss.
• Noise-induced hearing loss due to prolonged exposure to high-intensity sounds.
• Age-related hearing loss (presbycusis).
• Drug-induced hearing loss.
• Hearing loss caused by infections or viral infections, such as encephalitis, meningitis, rubella, measles, and chickenpox.
• Tumors of the vestibulocochlear nerve (cranial nerve VIII) or cerebellopontine angle tumors.
• Central nervous system disorders, such as cerebral infarction and intracerebral hemorrhage.
• Image of a left cerebellopontine angle tumor (yellow and blue arrows).

4. How Is Hearing Loss Diagnosed?

Hearing loss is diagnosed through hearing tests, with pure-tone audiometry being the primary method. In cases where pure-tone audiometry cannot be performed due to certain factors, such as developmental delay, young age, advanced age, or psychiatric conditions, objective tests such as auditory brainstem response (ABR) or auditory steady-state response (ASSR) may be used for diagnosis.

In addition, to comprehensively assess middle and inner ear function, tympanometry and acoustic reflex testing should also be performed.

4.1. Tympanometry and Acoustic Reflex Testing

Interpretation of Results:

• Normal result: hearing threshold ≤ 20 dB.
• Abnormal result: hearing threshold > 20 dB, indicating hearing loss of varying degrees as described above. Hearing loss may occur in one or both ears and may be conductive, sensorineural, or mixed.

5. What Should You Do If You Are Diagnosed with Hearing Loss?

An otolaryngologist will advise you on which additional tests may be needed, such as endoscopy, computed tomography (CT), magnetic resonance imaging (MRI), and other examinations, to determine the underlying cause and recommend an appropriate management approach, which may include medical treatment, hearing aids, or surgery.

The information above is for reference purposes only and is not intended as medical advice. Please contact your doctor for detailed medical consultation.