How We Hear & Hearing Loss
The Three Divisions of the Ear
The ear is actually a system of three interrelated parts that function together for the perception of sound and the maintenance of balance.
The Outer Ear
The outer ear is what most people consider “the ear”. It consists of the flexible, fleshy part (the pinna) as well as the ear canal. At the inner most part of the ear canal is tight membrane, the eardrum (tympanic membrane). The eardrum separates the outer ear from the middle ear space.
The Middle Ear
The middle ear is a space in the skull, which lies behind the eardrum and is in close proximity to many important structures. The bottom of the space is closely related to the carotid artery and jugular vein. At the front of the space is the opening of the eustachian tube (the conduit which connects the middle ear space to the back of the nose). The inner most wall has two openings to the inner ear, one for the stapes (the oval window) and one called the round window, both function in the transduction of mechanical sound to nerve impulses in the inner ear. In addition, a very important nerve, which controls the movement of the face and is involved in taste, runs along this bony wall in its own canal as it travels to exit the skull. The back most wall of the middle ear has an opening to a system of air cells located within the bone behind the ear (mastoid bone), called the mastoid air cells. Finally, three small bones span this space and conduct sound energy from the ear drum to the inner ear. These bones are called the malleus, the incus, and the stapes (a.k.a. the hammer, the anvil, and the stirrup). As you can see, the middle ear is a busy and very important area. This is also a common site of disease and hearing loss.
The Inner Ear
The inner ear is actually a series of fluid filled spaces housed within the bone of the skull. These spaces include the cochlea, which is involved in hearing, and the semicircular canals, which are involved in balance. Within these spaces, bathed in fluid, are delicate neurosensory tissues and fine nerve endings, which will ultimately conduct both balance and hearing information to the brain.
How the Ear System Works:
- Sound energy in the environment is collected and funneled to the eardrum by the fleshy part of the ear (the pinna) and the ear canal.
- The sound waves strike the eardrum causing it to vibrate.
- The vibrations are transmitted to the inner ear from the eardrum through the three bones spanning the middle ear space (the malleus, incus, and stapes).
- The base of the stapes sits in one of the openings to the inner ear (the oval window). The vibrations of the stapes produce waves in the fluid that fills the cochlea.
- The fluid pushes against the sensory membranes in the cochlea.
- This movement causes tiny sensory cells located here (hair cells) to transmit electrical impulses to delicate nerve fibers of hearing, which are attached to them.
- This impulse is then sent to the brain where it is interpreted as sound.
The balance system of the inner ear is very similar to that described above expect this system is activated by head motion (instead of sound vibrations transmitted through the ossicular chain).
Facts of Hearing Loss
- Twenty-five million people in the U.S. suffer from hearing loss of some type.
- 15-20% may benefit from a procedure to improve their hearing.
- o Most will benefit from hearing amplification, regardless of the type of hearing loss.
- Approximately 30% of people over the age of 65 and 70-80% over 75 years of age have a significant hearing impairment.
- Baby boomers are showing increased hearing loss at earlier ages.
- Hearing is an integral part of communication
- Studies have shown that hearing loss in the elderly reduces involvement in social activities and leads to feelings of isolation and depression.
- In children, hearing is essential for appropriate speech and language development.
Causes of Hearing Loss
There are many conditions that can cause hearing loss. Below some common causes are listed below and sometimes there may be multiple problems existing at the same time.
The Outer Ear
- Ear canal blockage with wax (cerumen) or a foreign body.
- Narrowing of the ear canal.
- Infection of the ear canal (otitis externa). Often this is accompanied by pain, drainage, itching and swelling.
The Middle Ear
- Improper formation of the ear bones from birth.
- A hole in the eardrum (tympanic membrane perforation).
- Infection in the middle ear space (otitis media)
- Dysfunction of the eustachian tube and fluid build up (serous otitis media).
- Skin cyst formation in the middle ear (cholesteatoma). This can perforate the eardrum, cause infection, and erode the ear bones or bone of the skull.
- Head injury with dislocation of the middle ear bones.
- Otosclerosis. This is an abnormal growth of bone around the base of the stapes bone, which prevents its proper motion.
The Inner Ear
- Gradual decline in hearing with aging (presbycusis).
- Sudden or prolonged very loud noise exposure.
- Gradual exposure over years to loud noise.
- Congenital or hereditary hearing loss.
- Certain viral infections.
- Certain skull fractures.
- Certain medications (diuretics, antibiotics, chemotherapeutic agents).
- Rarely, tumors of the hearing or balance nerve.
What is Tinnitus?
Tinnitus is very common and can be annoying and distracting. Almost 37 million Americans have tinnitus in their ear or ears. It may come and go or might be a constant bother. It might be soft or loud, low pitched (roaring), or high-pitched (ringing) kind of sound. More than 7 million people are so badly affected that they can’t lead normal lives.
What Might Cause Tinnitus?
There are various causes including a plug of wax, allergy, ear infection, circulatory problems, certain medications, and prolonged exposure to loud noise.
Tests for Hearing and Balance
All patients with hearing or balance problems will need certain tests performed as part of their diagnostic work up. Occasionally, these tests may need to be repeated, even if you have recently had them performed elsewhere. It is very important to determine the current status of your hearing and balance systems, to determine whether previous testing was accurate or to determine if any changes in the status of your hearing and balance systems have occurred.
Comprehensive Audiological Assessment
This consists of both pure tone and speech perception hearing tests, tympanometry and acoustic reflex testing. The testing occurs in a sound treated room using headphones or inserts that fit in the ear canal. During pure tone testing, a series of tones of differing frequency are presented to the patient at varying intensity levels (loudness) to determine the patients hearing level, the amount of hearing loss, and the type of hearing loss present at the different frequencies. A series of word lists are then used to both determine the lowest level at which a patient can hear the word (speech reception threshold) and their ability to correctly discriminate what words are being presented (speech discrimination score).
Tympanometry and acoustic reflex testing is used to determine the status of the eardrum, middle ear, reflexes of the auditory muscles, and associated auditory nerve pathways. A probe is placed in the ear for these tests. Tympanometry uses changes in pressure within the ear canal to determine the mobility of the eardrum, the bones of hearing (disrupted or frozen), and the status of the middle ear (if it contains fluid). It also gives a determination of the volume in the ear canal, which further allows us to assess whether the eardrum is intact. Acoustic reflexes are tests using loud noises presented to the ear to determine minute changes in the mobility of the eardrum. This is an indirect measure of the function of auditory muscles and the neural pathways that control them. Acoustic reflex decay is also measured which assesses whether the reflex can be maintained for at least 10 seconds. The absence of reflexes or the presence of reflex decay can be a significant finding for tumors of the hearing or balance nerve and may necessitate further diagnostic testing.
Otoacoustic Emissions (OAE)
Certain cells located in the organ of hearing (the cochlea) are involved in the conversion of sound vibrations into electrical signals, which are then transferred to the brain for interpretation. These cells are known as hair cells and are of the utmost importance in hearing. The otoacoustic emissions test is used to assess the function of these cells. A set of high frequency sounds are introduced into the ear after which the ear will emit minute sounds (emissions) in response to this stimulation which can then be measured by a computer. The presence of OAEs means that the hair cells are healthy and functioning normally. This test helps to determine the site of hearing loss and can also be used to identify hearing loss before it is manifested on a Comprehensive Audiological Assessment.
This test measures electrical potentials within the inner ear. This is thought to be related to fluid pressures within the inner ear. A ratio of these potentials is calculated. A large ratio may indicate an increase pressure in the inner ear, which can be associated with a particular ear condition known as Meniere’s disease. This test is often done in conjunction with the ABR test (see below) as it is generally ordered to evaluate similar ear symptoms and requires the same electrode setup.
Auditory Brainstem Response Test (ABR)
This test is used to evaluate the electrical pathway between the inner ear and the brainstem. A clicking sound is presented to one ear at a time. The electrical response to this sound stimulus is then recorded by the electrodes and averaged by a computer. A waveform will be produced that contains peaks corresponding to certain points in the central auditory pathway. The time for the electrical signal to progress between these peaks is then calculated by the computer and compared to well known normative data. Delays in response time can be important indicators of numerous disease processes that can affect the auditory pathway including tumors (acoustic neuroma), demyelinating diseases (multiple sclerosis), and vascular ischemic areas (strokes).
This powerful testing modality can be used to obtain auditory threshold testing at certain frequencies in patients unable or unwilling to perform conventional hearing tests. It can also be used to evaluate hearing in newborns and infants who are at high risk for hearing loss. This modality is occasionally used during acoustic tumor surgery to monitor hearing intraoperatively during tumor removal in an attempt to preserve hearing.
Electronystagmography (ENG) or Videonystagmography (VNG)
This is actually a battery of tests designed to evaluate the balance system. The balance system of the inner ear and eye movements are highly coordinated through central brain connections. These tests use electrodes or video goggles to record eye movements during this series of tests. Voluntary eye movements are recorded while following a light target on a wall. Involuntary eye movements are recorded in various body positions and during movement of the head to various positions. Involuntary movements are also recorded during thermal stimulation of the inner ear balance system with hot or cold air. If stimulation is successful you may feel a brief spinning sensation, which is normal. This will also induce certain eye movements, which again are recorded and interpreted. A reduced or absent response indicates dysfunction within the inner ear balance system.
Is it time for a hearing aid?
The best way to answer this question is to be honest with yourself! Are you having difficulty hearing people at a restaraunt or in a crowd? Are you having trouble hearing at meetings, church, work, or school? And, most importantly, are other people telling you that you can’t hear? Hearing loss is a normal and acceptable part of aging. If you notice any change in your hearing you should see a medical specialist. A thorough exam and hearing test will identify any hearing problems. Once a hearing loss is diagnosed a medical specialist will decide if a hearing aid or other medical treatments are necessary. If hearing aids are recommended, make sure there is a trial period offered which allows you to return the hearing aids at a low cost if the performance of the hearing aids is less than satisfactory.If a medical specialist recommends a hearing aid, you should ensure that the right hearing aid is being prescribed for your specific hearing loss. Hearing aids are highly sophisticated pieces of technology, and are not designed as a “one-size-fits-all” product. Your medical specialist’s staff should spend time to educate you about hearing aids and to find the specific aid that fits your hearing needs. There should be an ample trial period that allows you to return the hearing aids at a low cost. You should also be scheduled for return visits in order to discuss your experiences with the hearing aid so that it may be further tuned to meet your satisfaction.
Am I choosing the correct hearing aid, and am I getting a fair price?
Discuss styles and options with your hearing specialist. Together agree on a course of action. Comparison shopping can be a good idea, but, make certain that you are comparing the same styles and types of hearing aid. Not all aids that look the same have the same function. Oftentimes slightly less expensive aids are significantly less sophisticated, which means the sound quality and your satisfaction will be severely diminished. Hearing aid dealers and some franchises can be misleading. Don’t be fooled by savvy marketing and glamorous display cases!
Does it matter where I go for a hearing aid?
Does it matter where you get your glasses or who you see for other health-related issues? Certainly! You should always find a medical specialist that is highly trained with superior knowledge and skills to meet your hearing needs. You should feel comfortable, have an adequate understanding of the problem, and have all or your question answered to your satisfaction. Beware of dealers who are out to sell you something. Hearing aids are sophisticated pieces of technology. For some individuas they can be intimidating and confusing. You should ensure that your specialist possesses all the personality and skills to give you the best experience possible.
I can save money getting a hearing aid through the internet. Is this a good idea?
We do not recommend buying hearing aids over the internet, or buying used aids. For optimal performance and satisfaction, hearing aids need to be specifically sized and tuned for each individual. Improperly fit aids can cause trauma and infections in the ear, and can lead to worsening ear function!