About Hearing Loss
Hearing loss is categorized by its severity and location in the auditory system. The severity can range from "minimal" to "profound" and can be the result of damage to the outer ear, middle ear, inner ear, brain, or a combination of all four.
Hearing Loss Severity
Hearing loss is described by varying degrees, not percentages. Hearing loss may be slight/minimal, mild, moderate, moderately-severe, severe, or profound and vary across pitches (i.e. frequencies). The severity of a hearing loss is determined by a diagnostic hearing assessment. During this process, we determine the amount of volume, or intensity, needed to stimulate your hearing system at various pitches. We then compare this data to individuals with normal auditory systems, giving us your hearing loss severity.
We measure sound in decibels (dB), and the softest decibel level you can hear is considered to be your hearing threshold. Normal hearing thresholds for adults are considered to be 25 dB or less, whereas normal hearing thresholds for children are considered to be 15 dB or less.
Conductive Hearing Loss
Conductive hearing loss occurs when there is a problem with the way sound is "conducted" to the inner ear. The problem may lie in the outer ear (pinna or ear canal), eardrum (tympanic membrane), or the middle ear (bones/ossicles and Eustachian tube). In the image below we would be dealing with damage in area #1 and/or #2. The inner ear and auditory nerve remain unaffected in this type of hearing loss (i.e. #3, #4, #5). Conductive hearing losses are most commonly the result of an abnormality in the middle ear - often referred to as middle ear dysfunction. The middle ear is a complex mechanical system - any disruption with how vibrations are transmitted to the inner ear result in a conductive hearing loss.
Common Symptoms of Conductive Hearing Loss:
- Complain that people mumble
- Difficulty hearing people speak
- Aural fullness (ear feels plugged)
- Tinnitus (ringing/buzzing sound in ears)
Common Causes of Conductive Hearing Loss include:
- Outer ear infection (otitis externa or "swimmer’s ear")
- Middle ear infection (otitis media)
- Middle ear effusion (fluid behind eardrum)
- Negative middle ear pressure
- Complete cerumen occlusion (wax blockage)
- Deterioration of the middle ear ossicles (bones)
- Otosclerosis - fixation of the ossicles
- Perforated tympanic membrane (TM) - a hole in the eardrum
- Absence of the outer ear or middle ear structures (e.g. atresia)
Conductive hearing losses may be temporary or permanent, depending on the source of the problem. Medical management can correct, or partially correct, some cases of conductive hearing loss, while amplification may be a recommended treatment option in more long-standing or permanent cases.
Individuals with conductive hearing loss may report that sounds are muffled or quiet. Most individuals with conductive hearing losses do extremely well with amplification (i.e. hearing aids) because their inner ears are unaffected. This means that once sounds reach the inner ear, their hearing system works very well. In rare cases, individuals get limited benefit from acoustic hearing aids because there is too much damage to the middle ear or because of chronic otorrhea (i.e. fluid draining from ear). In these instances, a referral for a Bone Anchored Hearing System (BAHS) is made.
If a conductive hearing loss is diagnosed, a referral to an Otolaryngologist (Ear, Nose, and Throat Specialist) is usually recommended to investigate the cause, prognosis, and explore any available medical treatments (e.g. surgery, medications, etc.).
Sensorineural Hearing Loss
Sensorineural hearing loss (SNHL) most commonly occurs when there is a problem with the sensory receptors of the hearing system, specifically in the cochlea of the inner ear (#3 and #4 in the image below). The majority of sensorineural hearing loss occurs as a result of an abnormality or damage to the hair cells in the cochlea. The outer hair cells (OHC) tend to be affected first, with inner hair cell (IHC) damage typically occurring later. However, both outer and inner hair cell damage can be present in varying degrees at any time with sensorineural hearing loss. This damage prevents sound from being transmitted to the brain normally, resulting in hearing loss. When the damage is related to the sensory receptors in the inner ear we classify it as a "sensory" hearing loss. When the damage is attributable to nerve pathways beyond the cochlea (i.e. in the nerves that travel from the inner ear to the brain) we refer to it as a "neural" hearing loss (more information below). However, it is usually impossible to determine how much of hearing loss is directly related to sensory damage and how much is related to neural damage - this is where we get the name sensorineural (sensory+neural).
Common Symptoms of Sensorineural Hearing Loss:
- Complain that people mumble
- Can hear people talk, but often cannot understand what is being said
- Difficulty hearing in background noise
- Sound may be distorted
- Tinnitus (ringing/buzzing sound in ears)
Common Causes of Sensorineural Hearing Loss:
- Presbycusis – hair cells in the inner ear are damaged as a result of the aging process. Certain parts of the inner ear simply “wear out” over time, resulting in age-related hearing loss.
- Noise exposure – damage to the hair cells and sensitive nerve endings in the inner ear as a result of exposure to intense sound pressure (i.e. loud sound.) This damage usually occurs over a period of time (noise induced hearing loss), but can also be instantaneous if the sound is intense enough (acoustic trauma).
- Other hair cell damage – hair cells in the inner ear can also become damaged due to genetics, infections, drugs (ototoxic medications), trauma, or other medical conditions.
- Congenital – inner ear damage present from birth.
Sensorineural hearing losses are usually permanent and may remain stable or worsen over time. Routine hearing tests are needed to monitor the hearing loss. Amplification, including hearing aids or cochlear implants (in the most severe cases), is usually the best treatment option.
Mixed Hearing Loss
Mixed hearing loss occurs when a person has a sensorineural hearing loss in combination with a conductive hearing loss. It is, very literally, a mix of sensorineural and conductive hearing losses. This means there is a problem in the inner ear as well as in the outer and/or middle ear. As with conductive hearing losses, a referral to an Otolaryngologist/ENT is often recommended to investigate the conductive portion of the hearing loss to explore medical treatment options. However, the sensorineural portion of the hearing loss is usually best treated with hearing aids. Typical treatment involves both amplification (hearing aids) and a medical work-up by an ENT.
Neural Hearing Loss
Neural hearing loss most commonly occurs when the nerve that carries electrical impulses from the cochlea to the brain is damaged (vestibulocochlear nerve or cranial nerve VIII; #5 in the image below). It is difficult to determine the exact location of neural hearing loss, but it is somewhere in the nerves that carry auditory information from the inner ear to the brain.
Common Causes of Neural Hearing Loss:
- Head trauma
- In-utero exposure to certain infections
- Severe jaundice in infancy
- Low birth weight associated with premature birth
Individuals with neural hearing loss often have difficulty understanding speech, even when it is loud enough, as well as in background noise. Amplification may be recommended in some cases of neural hearing loss depending on the severity of the damage to the hearing nerve. Diagnosing neural hearing loss is extremely difficult - for this reason it usually gets grouped under the category of "sensorineural" hearing loss.
Sudden Hearing Loss
Sudden changes to hearing can occur for a multitude of factors and are considered a MEDICAL EMERGENCY. Ranging from less severe causes such as a wax blockage in the ear canal to more severe causes such as viral infections, membrane ruptures, or tumours. If you experience a sudden drop in your hearing, you should seek medical attention IMMEDIATELY. The effectiveness of certain treatments for sudden sensorineural hearing loss (SSNHL) greatly reduce if they are not started within 48 hours of onset. For some sudden sensorineural hearing losses, our likelihood of treating the loss greatly worsens the longer we wait.
SSNHL is usually unilateral in nature (i.e. only in one ear) and is most common between the ages of 40 and 54. Prognosis for SSNHL can vary; however, we typically see partial or full recovery in 75% of patients.
Some medical doctors and other health practitioners are unaware of the severity and time sensitivity of sudden hearing losses. Unfortunately treatment is often missed or prolonged because of misdiagnoses. If you or someone you know has experienced a sudden hearing loss, call us to book an appointment immediately or seek medical attention as soon as possible.