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Separating the outer ear from the middle ear is the eardrum, which vibrates the tiny bones (hammer, anvil, stirrup) in the middle ear. If the eardrum is completely missing from your ear then these bones won’t be able to vibrate as well as they should, causing a permanent hearing loss. Sometimes the eardrum is there but it’s damaged. You may have heard of a ruptured (or punctured) eardrum – that’s when the eardrum has a hole in it. Often these holes will repair themselves. When they don’t they can sometimes be repaired by an operation. But while the eardrum has a hole in it, it will cause a hearing loss – but it’s not always a serious one.
Another temporary cause of hearing loss is infection. You’ve probably noticed that when you get a cold you don’t hear so well. That’s because the middle ear fills up with liquid which prevents the hammer, anvil and stirrup from moving properly. The liquid can also push out the eardrum which prevents it from vibrating fully. Children are especially prone to this form of hearing loss, and it’s often accompanied by ear-ache. Sometimes the eardrum will rupture to relieve the pressure caused by the liquid and this usually eases the pain. The eardrum will repair itself more often than not.
The bones in the inner ear can either crumble or grow more bony. Otosclerosis, for example, can cause the stirrup to become fixed so it can't vibrate with the eardrum. Similarly the muscles that hold the bones in place may become weak. There are operations available that can correct these sorts of damage to the middle ear, but it’s not always practical or possible to perform them. If they remain damaged, or if they have to be removed, it will result in a hearing loss.
You may have noticed that if you’ve been in a noisy environment such as a disco or a factory your ears feel muffled after you come out (you may also get tinnitus). Next day, however, your hearing is back to normal. This is because our middle ear has a self-protection facility to prevent loud noises getting to the inner ear and permanently damaging our hearing. It works because the muscles in the middle ear that hold the hammer, anvil and stirrup in place temporarily tighten to prevent them moving so freely. Once out of the noisy environment the muscles begin to slacken off again and normal hearing begins to return. Unfortunately, though, over-exposure to loud noises can have a permanent effect, which we will look at in the next section.
We now move onto the most common cause of permanent hearing loss – damage to the inner ear or to the auditory nerve.
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