Presbycusis: Age-related hearing loss with gradually progressive inability to hear, especially high frequency sounds. Presbycusis most often occurs in both ears, although not necessarily at the same time or rate. Because the loss of hearing is so gradual, people with presbycusis may not realize that their hearing is diminishing. They may have trouble distinguishing and understanding conversation in a noisy setting. Environmental exposures (such as to guns, power tools, industrial machinery, or very loud music) contribute significantly to presbycusis, but up to half of presbycusis is genetically determined. Presbycusis is common, affecting a third of people between 65 and 75 years and up to a half of people 75 and over. The hearing loss can usually be corrected with a hearing aid.