Introduction
Hearing Loss
Hearing loss is the third most common chronic condition in North America. It is technically not the same as deafness or even a hearing deficit. It is estimated that one-third of those older than age 65 and one-half of those older than age 75 are living with some form of hearing impairment. Worldwide, the number is an estimated 500 million people.
Although commonly though of as an age-related condition, hearing loss can occur at any age, resulting from noise exposure, trauma, genetics, or illnesses. It was not until one of our granddaughters did not hear the school fire drill alarm that her problem was noticed. Before that time, she was thought to be naturally shy, saying little, and interacting even less. After testing, her hearing was found to be minimal. Her solution was to have a simple surgery. As a result, her personality rapidly became more outgoing and her classroom participation increased.
It is never too early to have a child tested. Babies considered to be high-risk for hearing loss include those with a medical history of:
- severe oxygen deprivation at birth
- exposure in the womb to such infections as German measles or syphilis
- exposure to herpes during the birth process
- an infection, as bacterial meningitis
- severe jaundice
- head trauma
- a nervous system disorder associated with hearing loss
- chronic ear infections
- a familial history of hearing loss
The most common frustration for those suffering from a hearing impairment is feeling uncomfortable in public because they miss so much of what is being said. Ludwig van Beethoven expressed as much in an 1802 letter to one of his brothers. Withdrawing from society is a natural result, causing other people to incorrectly judge this behavior.
It is also a common belief that hearing aids will solve the problem. This is not always so, but they can help in the majority of cases. However, only one in four of those who would benefit from a hearing aid actually wears one. Hearing aids have improved considerably since the conspicuous ear trumpets used in the 18th and 19th centuries.
Types of Hearing Loss Conductive hearing loss occurs when something blocks the pathway of sound waves to the inner ear. A common blockage results from ear wax buildup. Normally, the ear cleans itself, but in some cases, removal may require professional assistance. Other problems that can cause this type of hearing loss include foreign objects lodged in the ear, middle ear infections, head trauma, and abnormal bone growth in the region of the ear.
Sensorineural hearing loss happens as a result of damage to the structures of the inner ear. For instance, damage to hair cells in the cochlea or the nerve fibers leading from the cochlea to the brain is most often associated with the general wear and tear of aging (presbycusis) or with excessive exposure to noise. The initial damage is usually found at the base of the cochlea where the basilar membrane responds to high frequencies. This damage can result in difficulty in perceiving high-frequency sounds, as certain consonants in speech. For example, someone may have trouble distinguishing “tell” from “sell” or “miss” from “this”. Other causes of damage to the inner ear include high fever, chronic illness, certain medications, head trauma, or certain genetic disorders. The auditory nerve can also be damaged by abnormal growths or tumors, as well as by other causes.
Mixed hearing loss is a combination of the other two types. For example, someone with an age-related hearing loss may develop an ear infection. The conductive part of the hearing loss caused by the infection can usually be eliminated with medical treatment, but not the sensorineural damage.
Research
Research is ongoing as scientists try new approaches to treat sensorineural hearing loss. Unfortunately, their study focuses mainly on drugs that might reduce the effects of loud noise exposure on the inner ear and ones that may be used to inhibit the effects of aging on the hearing.
- Hair Cell Regeneration
One new area of research is hair cell regeneration. Hair cells are the delicate sensory receptors of the inner ear and damage to them results in serious hearing impairment. Until the mid-1980s, scientists believed the inner ear was incapable of producing new hair cells until they discovered that birds have a natural ability to do so. This led scientists to study if regeneration can take place in humans.
Researchers have successfully induced the first stage of hair cell regeneration in the inner ears of mammals other than humans. It is thought that human hair cells might be stimulated to regenerate through the use of hormone-like substances called growth factors, which control cell growth. Researchers are still testing various growth factors to determine which ones might cause hair cells to develop. Following that, they must then find a workable method to deliver these substances to the inner ear.
- Gene Therapy
Gene therapy, also known as gene transfer, is another area of research that has made dramatic progress, particularly in understanding the relationship between genetics and hearing loss. Researchers have discovered that many genes play a role and that genetics and environment likely interact to influence hearing loss. Gene therapy involves replacing a defective gene with a normal gene in a specific cell, hoping that the cell will use it. Gene therapy holds great potential for use in treating hereditary forms of deafness, preventing hair cell damage, and stimulating hair cell regeneration. This research is still at an early stage and has a long way to go before an affordable and accessible genetic treatment for hearing impairment is feasible.
One new area of research is hair cell regeneration. Hair cells are the delicate sensory receptors of the inner ear and damage to them results in serious hearing impairment. Until the mid-1980s, scientists believed the inner ear was incapable of producing new hair cells until they discovered that birds have a natural ability to do so. This led scientists to study if regeneration can take place in humans.
Researchers have successfully induced the first stage of hair cell regeneration in the inner ears of mammals other than humans. It is thought that human hair cells might be stimulated to regenerate through the use of hormone-like substances called growth factors, which control cell growth. Researchers are still testing various growth factors to determine which ones might cause hair cells to develop. Following that, they must then find a workable method to deliver these substances to the inner ear.
Gene therapy, also known as gene transfer, is another area of research that has made dramatic progress, particularly in understanding the relationship between genetics and hearing loss. Researchers have discovered that many genes play a role and that genetics and environment likely interact to influence hearing loss. Gene therapy involves replacing a defective gene with a normal gene in a specific cell, hoping that the cell will use it. Gene therapy holds great potential for use in treating hereditary forms of deafness, preventing hair cell damage, and stimulating hair cell regeneration. This research is still at an early stage and has a long way to go before an affordable and accessible genetic treatment for hearing impairment is feasible.
