Understanding Hearing Loss

How the Ear Works and Types of Hearing Loss

As can be seen in the accompanying cross section (Figure 1), the ear is comprised of much more than the visible skin and cartilage appendage on either side of our heads. A brief overview would begin with the outer ear, which extends from the auricle, or pinna, (what we call the “ear”) down the ear canal to the tympanic membrane, or eardrum. The larger the auricle the more effectively this is done. This is why when we are having trouble hearing we may cup our hand behind an ear. By doing so we can gather more sound waves.

The eardrum serves as the division between the outer ear and the middle ear. The middle ear is an air filled cavity which contains the auditory ossicles (ear bones). These bones, the smallest in the human body, are used in transmitting the sound energy from the vibrating eardrum to the cochlea.

The cochlea is the portion of the inner ear responsible for hearing. Within this fluid-filled, snail-shaped, bony capsule – only the size of a pea – the mechanical energy of the vibrating ear bones changes into an electromechanical energy by triggering the microscopic sensory “hair cells.” These hair cells, so named because of their appearance, send neural impulses to the brain for interpretation. (As an aside, a separately functioning portion of the inner ear attached to the cochlea [the semi-circular canals, visible in the cross section below as overlapping loops] is responsible for the sensation of balance and acceleration.)

Figure 1: Cross-section of the human ear

Figure 1: Cross-section of the human ear

Hearing loss may develop in any section of the ear. Hearing loss originating in the outer ear or within the middle ear structures is known as conductive hearing loss as these disorders keep sound from being effectively conducted through the hearing mechanism to the hearing-nerve receptors (the “hair cells”). Sources of conductive hearing loss include ear canal blockage from accumulated ear wax, damage or perforation of the eardrum, a fracture in the chain of small middle ear bones (the ossicles), a spongy-bone growth that stiffens the vibration of the middle ear bones (otosclerosis), or fluid accumulation in the normally air-filled middle-ear space.

The second, primary, type of hearing loss known as sensorineural hearing loss is commonly referred to as a nerve hearing loss. This loss most frequently is the result of prolonged or sudden exposure to intense noise or music or the result of structural deterioration with age. Other causes of sensorineural hearing loss may include hereditary factors, head trauma, viral infection, certain medications, systemic illness, and vasospasm. Certainly it is possible to have both a conductive hearing loss and a sensorineural hearing loss in the same ear. This is known as a mixed hearing loss.

The audiological examination in conjunction with the patient’s history is the primary means of differentiating between a conductive and sensorineural hearing loss. Within the pediatric population nearly 95% of hearing loss is conductive with the remaining 5% being sensorineural. Adult hearing loss is nearly the opposite with 5% being conductive and 95% being sensorineural. While conductive hearing loss most frequently can be corrected through medicine or surgery this is not the case with sensorineural hearing loss.

At Audiology Services we follow the guidelines established by the medical director at the Veteran’s Affairs Hospitals. This protocol recommends adult patients first be seen by an audiologist for a comprehensive evaluation. When a conductive hearing loss is identified the audiologist refers the patient back to his or her physician for possible medical treatment of the condition.

When sensorineural hearing loss is identified the most common treatment is the guided use of properly selected personal amplification and/or assistive listening devices.

Prevalence, Impact and Degrees of Hearing Loss

While hearing loss can occur at any age, including birth, the prevalence of hearing loss clearly increases with age. It has been estimated that the number of persons with hearing loss in the United States over the age of 65 years will reach nearly 13 million by the year 2015. The number of children with permanent hearing loss is far fewer than the number of adults. However, the prevalence of hearing loss in children is almost staggering if we consider those children whose speech and language development and academic performances may be impacted by mild transient ear infections so common among children. While not all children have problems secondary to ear pathologies, 90 percent of children in the United States will have at least one ear infection before 6 years of age.

The impact of hearing loss cannot be addressed until diagnosed, and, left untreated, hearing loss among adults can seriously erode relationships both within and outside of the family unit. Research has demonstrated that among older adults hearing loss is related to overall poorer health, decreased physical activity and depression and may be associated with progressive physical and psychosocial dysfunction. Among younger adults, untreated hearing loss can increase levels of frustration, anger, social isolation and marital strife.

The degree of hearing loss can vary greatly between any two people. Between the two extremes of hearing well and hearing nothing, there are many degrees of impairment. The terms used to describe the degree of hearing loss are mild, moderate, severe and profound. Most hearing losses are mild to moderate and all degrees of hearing loss can be helped.

  • Mild hearing loss results in an inability to hear soft sounds and an increased difficulty understanding speech clearly in noisy environments. Mild gain amplification can reduce the aggravations accompanying this degree of hearing loss. Some may only require the use of select assistive listening devices such as TV or telephone amplifiers.
  • Moderate hearing loss results in an inability to hear soft as well as moderately loud sounds, and can create considerable difficulty understanding speech, particularly within background noise. An audiological evaluation will determine the best approach to address these problems.
  • Severe hearing loss allows some loud sounds to remain audible but communication without hearing instruments is impossible. The audiologist can help select the most appropriate hearing aids and the types of assistive listening devices that may be most helpful.
  • Profound hearing loss may allow some extremely loud sounds to be audible but life without some form of assistance quickly leads to isolation from all spoken communication. Many with this degree of hearing loss are candidates for a cochlear implant and should consult with their audiologist about this possibility.