After the age of 40, various organs in the body begin to age and degenerate, particularly in the sensory organs, with deafness and blurred vision being the most prominent manifestations. The degree of aging can vary from person to person; some may experience severe deafness as early as 50, while others may retain good hearing even past 80. Age-related hearing loss is both physiological and pathological, influenced by a combination of internal bodily factors and external environmental conditions.

bubble_chart Etiology

1. Long-term exposure to noise: According to Rosen's research, the hearing of people in remote tribes in the Sudan region is better than that of urban residents, especially among those over 65 years old, who often maintain good high-frequency hearing. Weston (1964) found that the onset of presbycusis in urban residents occurs earlier than in rural areas. The reasons for this are multifaceted, but long-term noise injury is one of the primary causes.
2. The influence of different dietary habits: According to a Soviet survey (1976) comparing the hearing of residents in Moscow and Georgia, the latter region, where people consume more vegetarian diets, has a lower incidence of coronary heart disease, and the elderly generally maintain better hearing. In contrast, Moscow residents primarily consume meat, have higher blood cholesterol levels, a higher incidence of heart and blood vessel diseases, and poorer hearing among the elderly. Rosen (1962) found that elderly individuals on a low-saturated-fat diet had an average blood cholesterol level of 5.2 mmol/L, while those on a saturated-fat diet had levels as high as 6.76 mmol/L. Weston (1964) found that 70% of elderly individuals with deafness suffered from atherosclerosis, and the severity of deafness was positively correlated with the degree of atherosclerosis.
3. Genetic factors: Lowell (1977) divided deafness patients into two groups by age. Those under 65 with a family history of deafness exhibited flat or trough-shaped hearing curves, while those over 65 without a family history showed descending hearing curves with low speech recognition rates, indicating a dominant genetic influence. In terms of genetics, there are also differences between genders. Women have greater tissue tolerance than men, and men are more exposed to harsh environments and noise injury, smoke and drink more than women, leading to a prevalence of presbycusis in men twice that of women.

bubble_chart Pathological Changes

1. Age-related degeneration of the middle ear: Such as thickening of the tympanic membrane, reduced elasticity, loosening or calcification of the ossicular ligament, can lead to conductive hearing impairment. According to Nixon et al. (1962), age-related degeneration of the middle ear results in only a 12dB hearing loss at 4kHz, so the impact is minimal.
2. Degeneration of the inner ear: Age-related degeneration of inner ear cells manifests as reduced nuclear division, decreased nuclear protein synthesis, and accumulation of pigments and insoluble substances in the cytoplasm, leading to cellular degeneration and atrophy. Schuknecht (1955) classified presbycusis into four types based on pathological changes in different regions:
   1. Sensory presbycusis: Atrophy and degeneration begin in childhood or middle age, progressing slowly and mostly confined to the organ of Corti in the basal turn of the cochlea, spanning a few millimeters. Early stages show distortion and flattening, followed by the disappearance of supporting cells and hair cells, leaving only the basilar membrane. Clinically, this presents as a sudden high-frequency hearing loss with a descending audiogram, while speech recognition remains relatively intact.
   2. Neural presbycusis: Neurons in the auditory nervous system gradually decrease with age, most notably in the basal turn, and may extend to higher central pathways. Hearing remains unaffected early on until neuronal damage disrupts effective signal transmission. The main feature is severe impairment in speech recognition despite relatively preserved pure-tone hearing, creating a disproportionate discrepancy. Otte (1978) studied changes in the spiral ganglion and found that the average number of neurons decreases from 37,000 at ages 1–10 to 20,000 after 80, and may drop to 13,000 in individuals with presbycusis. This phenomenon can be termed age-related speech deterioration.
   3. Strial presbycusis: A common form of presbycusis, where the stria vascularis undergoes progressive degenerative changes between ages 30–60, appearing as patchy atrophy, most severe at the cochlear apex with cystic changes. Due to impaired endolymph circulation, all three layers of the stria vascularis atrophy, leading to hearing loss across all frequencies, resulting in a flat audiogram. Early speech recognition remains relatively good, but declines significantly once pure-tone loss exceeds 50dB.
   4. Cochlear conductive presbycusis: Named by Schuknecht (1974), this lacks definitive histopathological evidence and is also called mechanical presbycusis. It first appears in middle age, possibly due to dysfunction in cochlear duct mechanics. The primary changes are hyaline degeneration and calcification of the basilar membrane, causing it to widen, thicken, and stiffen, impairing sound wave transmission. If conditions like otitis media, otosclerosis, or Ménière’s disease occur during life, they may combine with age-related degeneration, resulting in severe mixed deafness.
3. Central pathology: Age-related degeneration also affects the central auditory pathways. Hansen (1965) observed atrophy in the cochlear nuclei, superior olivary nuclei, inferior colliculi, and medial geniculate bodies of elderly individuals with hearing loss. Arensen (1982) found that the number of cochlear nucleus cells in elderly individuals with hearing loss was 50,600, about half the normal count of 96,400. This type of deafness is characterized by rising high-frequency thresholds, poor speech recognition and sound localization, and impaired ability to recall long sentences.

bubble_chart Clinical Manifestations

The tympanic membrane is normal. After middle age, there is progressive bilateral symmetric sensorineural deafness, accompanied by high-pitched tinnitus, starting with a decline at 3000Hz and gradually affecting the mid-frequency range of 4000–6000Hz. High-frequency hearing loss may also occur suddenly due to rupture of the basilar membrane. Generally, in conversation, men's voices are easier to understand than those of women and children. Pure-tone audiometry, based on the four pathological changes mentioned above, may show various sensorineural deafness curves, such as flat or descending patterns, with poor speech discrimination and tone decay. Bunch (1931) found that human hearing declines progressively with age. In 1957, the Hearing Research Center in Wisconsin, USA, developed a standard presbycusis curve chart, which can be used to estimate normal hearing levels at different ages. This chart shows that hearing remains relatively stable in individuals aged 70–90 and above.

bubble_chart Diagnosis

According to the history of presbycusis, the tympanic membrane is generally normal, pure tone audiometry shows a flat or descending hearing curve, with tone decay, and speech recognition rate is significantly reduced, making the diagnosis not difficult.

bubble_chart Treatment Measures

Pay attention to physical health early on, avoid prolonged exposure to noise, and reduce intake of saturated fats to prevent age-related cardiovascular diseases. If high-frequency hearing thresholds decline, take cholesterol-lowering medications, vasodilators, and large doses of vitamins A, D, and E. For severe hearing loss, hearing aids can be considered. Unfortunately, such deafness is difficult to reverse, and patients often struggle to tolerate amplified sounds due to poor speech recognition, making it challenging to find suitable hearing aids.