Adequate hearing is essential to maintain a connection with the outside world. In general terms there are 2 main components to our hearing, the conductive component and the sensori-neural (nerve) component.
Both of these components can be affected by inherited and aquired conditions. This can range from simple mechanical problems such as wax impaction in the ear canal and fluid behind the ear drum, to molecular changes affecting cochlear hair cells and tumours compressing the nerve of hearing.
Any degree of hearing loss requires careful measurement and assessement. As there is a wide range of possible pathologies there is a wide range of treatments that may be required.
Summary of common causes of hearing loss
Presbycusis (age related hearing loss) is the most common form of hearing loss. It is the predominant neurodegenerative disease of ageing. It is generally slowly progressive, symmetric and irreversible, and in some has a genetic predisposition. It classically affects the higher freqencies and in early cases causes hearing difficulties especially in the presence of background noise.
Noise induced hearing loss is the commonest preventable form of sensorineural hearing loss. Prolonged exposure to noise creates damage to cochlear hair cells, microscopic components of the inner ear that are responsible for converting sound waves into an electric neural signal that is perceived as sound. When exposed to loud noise the ear can react by creating a sensation of tinnitus or ringing in the ear. Initially this is self resolving and is termed a temporary threshold shift. Repeated and extended exposure to loud noise can then lead to permanent damage. As a general guidline permanent damage can occur after exposure to noise at 85dB after 8 hours. For every 3dB rise in noise input, the ear can last half that time. So at 88dB, 4 hours is the maximum exposure. 91dB 2 hours, 94dB 1 hour, 97dB 30 minutes, 100dB 15minutes and so on. As a guide to the level of environmental noise, a chainsaw runs at 100dB. The level of noise within a nightclub however also runs around the 100dB level.