Types of hearing loss
There are three types of hearing loss depending what part of the hearing system is involved. These are conductive hearing loss, sensorineural hearing loss and mixed hearing loss.
Conductive Hearing Loss
Conductive hearing loss occurs when sound is not being conducted efficiently through the outer and middle ears, including the ear canal, eardrum, and the tiny bones, or ossicles, of the middle ear. Conductive hearing loss usually involves a reduction in sound pick-up level, or the inability to hear faint sounds.
This type of hearing loss can often be corrected through medicine or surgery. Conditions that may cause a conductive hearing loss include the absence or malformation of the pinna, ear canal, or ossicles; the presence of a foreign body in the ear canal; impacted ear wax (cerumen); fluid in the middle ear associated with colds, allergies, ear infections (otitis media); or a poorly functioning Eustachian tube.
Sensorineural Hearing Loss
Sensorineural hearing loss occurs when there is damage to the inner ear (cochlea) or to the nerve pathways from the inner ear (retrocochlear pathway of the acoustic nerve) to the brain. Sensorineural hearing loss not only involves a reduction in sound level, or inability to hear faint sounds, but also affects speech understanding or ability to hear clearly, particularly in noisy environments.
Sometimes a sensorineural hearing loss may result in a reduced tolerance to loud sounds and reduced appreciation of music. Sensorineural hearing loss can be caused by diseases, birth injury, drugs that are toxic to the auditory system (ototoxic), and genetic disorders.
Sensorineural hearing loss may also occur as a result of noise exposure, viruses, head trauma, aging, and tumours. Sensorineural hearing loss cannot be corrected medically or surgically. It is a permanent loss.
Mixed Hearing Loss
Sometimes a conductive hearing loss can occur in combination with a sensorineural hearing loss. This is called a mixed hearing loss. In other words, there may be a problem in the outer or middle ear and a problem in the cochlea or auditory nerve.