Presbyacusis

Presbycusis, or age-related hearing loss, is the cumulative effect of aging on hearing. Also known as presbyacusis, it is defined as a progressive bilateral symmetrical age-related sensorineural hearing loss. The hearing loss is most marked at higher frequencies.

Presentation
Deterioration in hearing has been found to start very early, from about age 18 years. The ISO standard 7029 shows expected threshold changes due purely to age for carefully screened populations (i.e. excluding those with ear disease, noise exposure etc), based on a meta-analysis of published data (Robinson & Sutton 1979). Age affects high frequencies more than low, and men rather more than women. One early consequence is that even young adults lose the ability to hear very high frequency tones above 15 or 16kHz. Despite this age-related hearing loss may only become noticeable later in life. The effects of age can be exacerbated by exposure to environmental noise, whether at work or in leisure time (shooting, music, etc). This is Noise-induced hearing loss (NIHL) and is distinct from presbycusis.

Over time, the detection of high-pitched sounds becomes more difficult, and speech perception is affected, particularly of sibilants and fricatives. Both ears tend to be affected.

Pathophysiology
Examples of microscopic changes seen in this condition are hair cell degeneration of the cochlea and giant stereociliary degeneration.

Causes
Factors responsible for presbycusis include:
 * Heredity: Features like early aging of the cochlea and susceptibility of the cochlea for drug insults are genetically determined.
 * Atherosclerosis: May diminish vascularity of the cochlea, thereby reducing its oxygen supply.
 * Dietary habits: Increased intake of saturated fat may accelerate atherosclerotic changes in old age.
 * Diabetes: May cause vasculitis and endothelial proliferation in the blood vessels of the cochlea, thereby reducing its blood supply.
 * Noise trauma: Exposure to loud noise/music on a continuing basis stresses the already hypoxic cochlea, hastening the presbycusis.
 * Smoking: Is postulated to accentuate atherosclerotic changes in blood vessels aggravating presbycusis.
 * Hypertension: Causes potent vascular changes, like reduction in blood supply to the cochlea, thereby aggravating presbycusis.
 * Ototoxic drugs: Ingestion of ototoxic drugs like aspirin may hasten the process of presbycusis.

Cultural aspects
Recently, the ability of young people to hear high frequency tones that are inaudible to others over 25 or so has led to the development of technologies to stop younger people from loitering near British shops (The Mosquito), and the development of a cell phone ringtone, Teen Buzz, for students to use in school, that many older instructors are unable to hear. In September 2006 this technique was used to make a dance track called 'Buzzin'. The track had two melodies, one that everyone could hear and one that only younger people could hear.