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. Properly speaking, hearing loss that accumulates with age but is caused by factors other than normal aging is not presbycusis, although separating out the individual effects of multiple causes of an individual’s hearing loss can be difficult.
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. 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 16 kHz. 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.
Factors that can cause hearing loss 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.