Table 1.

Classification and characteristics of presbycusis.

Classification		Pathologic characteristics	Characteristics of hearing impairment
Sensory presbycusis		Atrophy and degeneration of HCs [20].	An abrupt high-tone hearing loss [22].
Metabolic presbycusis		Speckle-like atrophy and cystic changes of SVs [23].	A flat audiogram and almost normal word discrimination [24].
Neural presbycusis		Regressive deterioration of SGNs [25,26].	The decline in word discrimination was disproportionate to the increase in pure-tone hearing thresholds [21].
Mechanical presbycusis		Conduction disorders in the inner ear, without cochlear pathological damage [27].	A slowly descending audiogram is mainly characterized by high-frequency hearing loss [8].
Mixed presbycusis		A combination of two or more pathological types mentioned above [21].	No specific audiogram pattern was observed [28].
Other presbycusis	Indeterminate presbycusis	No correlation was observed between audiometric patterns and cochlear pathological changes [29].
	Central presbycusis	The auditory segment of the central nervous system exhibits age-related modifications [30].