There are three major types of hearing loss: Conductive, Sensorineural, and Mixed
Conductive hearing loss is caused by a problem in the outer or middle ear, or from a defect in the ossicular chain. Conductive hearing loss can often be medically treated. Blockage of the external ear canal by either impacted earwax or a foreign body can produce a conductive hearing loss. Otitis media is the condition often referred to as an ear infection. When Otitis media occurs, fluid accumulates behind the eardrum in the middle ear space. This space is normally filled with air in a healthy ear. Otitis media is the most common cause of hearing loss in children and should be treated by a physician. Otosclerosis can cause conductive hearing loss. It is a condition in which the stapes bone of the middle ear begins to grow a “spongy” bone that prevents it from vibrating properly in the oval window.
Sensorineural hearing loss is the most common type of hearing loss and is caused by damage to the inner ear and/or the auditory nerve. Noise exposure, diseases, certain medications and aging can destroy parts of the inner ear and cause permanent hearing loss. If a sound is loud enough, a patient with inner ear damage may hear better. The undamaged parts of the cochlea transmit sound to the auditory nerve and on to the brain. Sensorineural hearing loss is also characterized by a lower tolerance to loud sounds called recruitment. Sensorineural hearing loss usually affects the high frequencies, which impairs a patient’s ability to differentiate consonant sounds and thus the fine distinctions in words such as “fit” versus “sit”. Most sensorineural hearing losses can be treated effectively with hearing instruments.
When a patient has a unilateral sensorineural hearing loss, the problem may be beyond the inner ear or cochlea, somewhere in the brainstem or brain. Though very rare, one cause of this type of hearing loss is a lesion (tumor) on the auditory nerve or on the brainstem. These lesions are usually slow growing and difficult to detect. An audiologist can administer special tests and refer you to an Otologist (ear surgeon) if he is suspicious of such a tumor.
Presbycusisis the sensory loss that is due to degenerative changes associated with the aging process. Presbycusis is the most common cause of sensorineural hearing loss in the adult population. Some statistics indicate that as many as 30% of those in the 65-70 age category will suffer from the effects of presbycusis. The percentage increases to 40% of those over 75 years of age.
Noise-Induced Hearing Loss is the second most common cause of acquired sensorineural hearing loss.The adverse effects of noise on the ear cause damage to tiny “hair cells” in the inner ear. When the hair cells become damaged from exposure to a single noise exposure such as gunfire or to prolonged exposure to loud noises such as music, machines, motors and other noise producing equipment, they are unable to be stimulated properly by an incoming sound signal. Once these hair cells have become damaged there is no way to repair them.
Sudden Hearing Loss is an abrupt loss of hearing in one or both ears. Known causes are drugs, trauma, infection, or disease. There are many instances when no cause can be found. Fortunately, one third of patients completely recover their hearing, another third partially recover their hearing, and the last third of patients never recover their hearing and the hearing loss becomes permanent. Steroid therapy sometimes increases the chance of recovery.
When a patient has both a conductive hearing loss and a sensorineural hearing loss, it is called a “Mixed Hearing loss”. For example, if a child who has a permanent sensorineural hearing loss develops an otitis media, the effects of the two types of hearing loss combine to create a greater hearing loss.