Degrees and Types of Hearing Loss
Degrees of Hearing Loss
Hearing loss can be categorized into varying degrees such as mild, moderate, moderately-severe, severe, or profound. Hearing loss is measured on a scale from mild to profound, and this explains why two patients with hearing loss may have different difficulties with their hearing. This is also why two patients with hearing loss may be recommended different hearing aids - some hearing aids fit more severe hearing losses than others. The audiological hearing evaluation can determine the amount of loss you experience, and compare it to listeners with hearing in the normal range.
The volume of sounds you hear is measured in decibels (dB). Someone with normal hearing has hearing thresholds within the 0 dB HL to 25 dB HL range. If the audiologist measures your hearing thresholds outside of this range of normal, you have hearing loss.
Mild hearing loss: 25-40 dB HL
Moderate hearing loss: 41-55 dB HL
Moderately-severe: 56-70 dB HL
Severe: 71-90 dB HL
Profound: 91+ dB HL
The average decibels of a normal conversation is 60 dB, a whisper is 30 dB, leaves rustling are 30 dB, a snowmobile is 106-115 dB, and firearms are 140-175 dB. Depending on your degree of hearing loss, you may easily hear some of these sounds, but not others.
An individual with a mild hearing loss may have no trouble conversing with a friend one-on-one or in a small group, but may struggle to follow the conversation when there is background noise or music. A patient with a moderate hearing loss may have trouble hearing when their partner is speaking, but not facing them, or when their name is called from behind.
The patient below has normal hearing in his right ear and a mild-moderate conductive hearing loss in the left ear. The hearing loss in the left ear was temporary and due to wax buildup.
The patient below has normal hearing in both ears. The patient had no specific concerns prior to the diagnostic hearing evaluation, but wanted a baseline hearing assessment.
This patient has normal hearing at the low frequencies and drops to a profound hearing loss by the high frequencies. This patient has hearing loss caused by noise exposure at work - Noise Induced Hearing Loss.
In addition to determining how much hearing loss you have, the audiologist can define the type of hearing loss. Some hearing losses are temporary (e.g. due to an ear infection), some may be treatable by surgery (e.g. tympanic membrane perforation), and some hearing losses are permanent. The three most common types of hearing loss are conductive hearing loss, sensorineural hearing loss, or mixed hearing loss.
Types of Hearing Loss
Conductive Hearing Loss
Conductive hearing loss occurs when there is a problem with the outer or middle ear. The problem may lie in the ear canal, the eardrum, or the middle ear (middle ear bones/ossicles or Eustachian tube). The inner ear (cochlea) and auditory nerve are functioning normally. The patient with a conductive hearing loss may perceive sounds and voices as soft or muffled, and may say that their ears feel plugged.
Some causes of conductive hearing loss include:
Outer or middle ear infections
Complete earwax blockage (cerumen impaction)
Separation of the middle ear bones (ossicular chain discontinuity)
Stiffness or fixation of the middle ear bones (otosclerosis)
A hole in the ear drum (tympanic membrane perforation)
Absence of the outer ear or middle ear structures
Conductive hearing loss may be temporary or permanent, depending on the cause of the hearing loss and whether surgery performed by an Otolaryngologist is recommended. Medical management can correct some cases of conductive hearing loss, while hearing instruments may be a recommended treatment option in long-standing or permanent cases.
Sensorineural Hearing Loss
Sensorineural hearing loss occurs when there is a problem with the inner ear (cochlea) or auditory nerve. The majority of sensorineural hearing loss occurs as a result of damage to the hair cells in the cochlea, or the connection between the hair cells and the auditory nerve. This abnormality prevents sound from being transmitted to the brain, and as a result, the sound is not heard by the individual.
Individuals with sensorineural hearing loss may say that speech is unclear or muffled. They may also have tinnitus (ringing in the ears).
There are many potential causes of sensorineural hearing loss including, but not limited to:
Congenital: the hair cells or auditory nerve has been abnormal since birth. The patient was born with this hearing loss
Noise Induced Hearing Loss (NIHL): the hearing loss is due to exposure to noise. This could be occupational noise or noise exposure within the patient’s personal life
Presbycusis: hearing loss due to aging
Trauma: this hearing loss is the result of trauma to the inner ear structures. This may have multiple causes including a motor vehicle accident, head injury from sports, or drugs including chemotherapy.
Sensorineural hearing loss is generally permanent. The hearing loss may remain stable over time or get worse over time, and routine hearing tests are needed to monitor the hearing loss. Hearing aids are the most common and successful treatment for sensorineural hearing loss.
Mixed Hearing Loss
Mixed hearing loss occurs when a person has a sensorineural hearing loss in combination with a conductive hearing loss. This means there is hearing loss in both the outer and/or middle ear, as well as the inner ear. The hearing loss that is in the outer/middle ear (conductive hearing loss) may be temporary or permanent, depending on the cause of the hearing loss, while the sensorineural component to the hearing loss is permanent. Mixed hearing loss is commonly treated with medical management and hearing aids.