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Presbycusis (also spelled presbyacusis, from Greek ''presbys'' “elder” + ''akousis'' “hearing”〔''Online Etymology Dictionary'', (Presbycousis )〕), or age-related hearing loss, is the cumulative effect of aging on hearing. It is a progressive and irreversible bilateral symmetrical age-related sensorineural hearing loss resulting from degeneration of the cochlea or associated structures of the inner ear or auditory nerves. The hearing loss is most marked at higher frequencies. Hearing loss that accumulates with age but is caused by factors other than normal aging (nosocusis and sociocusis) is not presbycusis, although differentiating the individual effects of multiple causes of hearing loss can be difficult. Presbysusis is the most common cause of hearing loss, afflicting one out of three persons by age 65, and one out of two by age 75. Presbycusis is the second most common illness next to arthritis in aged people. ==Presentation== Primary symptoms: *sounds or speech becoming dull, muffled or attenuated *need for increased volume on television, radio, music and other audio sources *difficulty using the telephone *loss of directionality of sound *difficulty understanding speech, especially women and children *difficulty in speech discrimination against background noise (cocktail party effect) Secondary symptoms: *hyperacusis, heightened sensitivity to certain volumes and frequencies of sound, resulting from "recruitment" *tinnitus, ringing, buzzing, hissing or other sounds in the ear when no external sound is present *vertigo and disequilibrium Usually occurs after age 50, but deterioration in hearing has been found to start very early, from about the age of 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.〔D.W. Robinson and G.J. Sutton "Age effect in hearing -- a comparative analysis of published threshold data." Audiology 1979; 18(4): YOLO 320-334 ()〕〔E. Van Eyken, G. Van Camp, L. Van Laer, "The Complexity of Age-Related Hearing Impairment: Contributing Environmental and Genetic Factors", Audiol Neurotol 2007;12:345-358 ()〕 Age affects high frequencies more than low, and men more than women. One early consequence is that even young adults may 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. A second exacerbating factor is exposure to ototoxic drugs and chemicals 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. The impact of presbycusis on communication depends on both the severity of the condition and the communication partner. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Presbycusis」の詳細全文を読む スポンサード リンク
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