Understanding Hearing Loss Correctly

Hearing Loss ≠ Deafness

If you find that the sounds you hear have decreased, or that the world around you has changed in tone, it indicates that you may have hearing loss. Some people might say, "What? I don't have hearing problems; I'm not deaf!"

In fact, deafness and hearing loss are not entirely the same thing! Hearing loss does not mean that you cannot hear sounds at all. Instead, it means that you cannot hear sounds normally. It includes "any reduction in auditory sensitivity, elevation of hearing thresholds, auditory functional disorders, or hearing loss caused by any reason."

 

Nature and Degree of Hearing Loss

After correctly understanding hearing loss, let's take a look at the classification of hearing loss. In general, hearing loss is mainly classified based on its nature and degree in clinical practice.

Most Common in Clinical Practice

The most common types of hearing loss in clinical practice are conductive hearing loss, sensorineural hearing loss, and mixed hearing loss.

Any structural or functional disorder in the outer or middle ear that weakens the sound energy entering the inner ear results in conductive hearing loss.

Affected Areas: Outer ear, middle ear

Common Clinical Ear Diseases:

Outer ear: Cerumen impaction, otitis externa, etc.

Middle ear: Tympanic membrane perforation, acute/chronic otitis media, discontinuity of the ossicular chain, etc.

When there is damage to the cochlea, auditory nerve, auditory pathway, or neurons at various levels, resulting in disorders in sound perception, neural impulse transmission, and cortical function, they are respectively referred to as cochlear, neural, and central hearing loss. When it is not possible to distinguish between them, they can be collectively referred to as sensorineural hearing loss.

Affected Areas: Inner ear cochlea, auditory nerve, and auditory pathway

Common Clinical Ear Diseases:

Cochlear: Drug-induced deafness, presbycusis, Ménière's disease, etc.

Post-cochlear: Auditory neuropathy, acoustic neuroma, etc.

 

Hearing loss caused by damage to both the outer and/or middle ear and the inner ear is called mixed hearing loss.

Affected Areas: Outer ear, middle ear, inner ear cochlea, auditory nerve, and auditory pathway may all be involved

Common Clinical Ear Diseases: Lesions may exist in the middle ear, inner ear, or post-cochlear area, such as otitis media that has not healed and spread to the inner ear.

 

How to Grade

Generally, in hospitals or professional hearing aid fitting centers, pure-tone audiometry can accurately measure the degree of hearing loss. The main test involves determining the lowest sound level that a patient can hear at different frequencies, known as the pure-tone hearing threshold.

The following is an audiogram. From left to right, the sound frequencies range from low to high; from top to bottom, the sound intensity increases. The lower the threshold on the graph, the more severe the hearing loss.

 

The red curve on the graph represents the right ear's air conduction threshold, while the blue curve represents the left ear's air conduction threshold. The clinical classification of hearing loss severity is based on the average air conduction threshold of both ears (as indicated by the arrow in the figure below).

 

The World Health Organization (WHO 1997) defines four categories of hearing loss severity: mild, moderate, severe, and profound.

In 2021, the WHO refined the grading of hearing loss and revised the definition of mild hearing loss from 25 dB to 20 dB.

After gaining a general understanding of hearing loss, what impact does it have on us, and how can we intervene to protect residual hearing? These questions will be answered in the next installment.