**6. Tinnitus**

Tinnitus is derived from a Latin verb tinnire (to ring), and it describes the conscious perception of hissing, sizzling, or ringing sound in the absence of a corresponding external stimulus. Tinnitus can sometimes be random voices, music, or a mixture of sounds [181]. It can be constant or intermittent, or may be perceived in one (mostly left) or both ears, or centrally within the head. The reason for the leftsided predisposition of tinnitus is yet unknown.

Most of the studies to investigate the prevalence of tinnitus have been carried out in USA or Europe which gave a rough estimate of 10–15% of individuals suffering from tinnitus in these populations. National Study of Hearing in England was one of the largest (n = 48,313) and most reliable studies conducted to determine the prevalence of tinnitus among adult population. The results showed a prevalence of 10–15% among adults. Similarly, results from studies in Egypt [182, 183], Japan [184–186], and Nigeria [187, 188], also indicated that the rate of prevalence of tinnitus in these countries is analogous to the results from the Europe [189] and the USA [190–192].
