||Two main types of presbycusis may be distinguished: peripheral and central presbycusis.
The hearing loss in peripheral or sensory presbycusis progresses slowly even in patients of advanced age.
With peripheral presbycusis, there is a high-frequency sensory hearing loss, with commensurate changes in discrimination.
The histopathologic changes associated with peripheral presbycusis consist initially of a slight distortion and flattening of the organ of Corti, followed by a loss of both the supporting and the sensory cells in the basal turn of the cochlea. Eventually the organ of Corti may disappear completely from the basal turn. There is a concomitant loss of the cochlear neurons, which is presumed to be a consequence of the injury to the afferent nerve endings and has been called secondary or retrograde neural degeneration. Decreased speech discrimination scores have been closely linked to a decrease in the population of cochlear neurons. The nerve processes of the spiral ganglion supplying the damaged hair cells may be missing, with empty nerve channels evident within the bony spiral lamina and at the habenula perforata. A proportionate loss of the ganglion cells may be seen within the modiolus, where the cell bodies are often replaced by loose or organized fibrous tissue. There is also usually evidence of strial atrophy, with compact collagen deposition and occasional hyalinization.