Cochlear implants are a really exciting intervention, probably the most important intervention in
Ear Nose and Throat Surgery in the last 30 years. They enable patients that have profound
hearing loss to go from not being able to hear anything to being able to communicate
normally and to be able to get normal jobs, the kids that have profound hearing loss can
go to normal schools and develop normal language. What they are is essentially an electrical
device that stimulates the cochlear nerve where the cochlea itself is unable to pick
up sounds and there are two components to it – the first is an implantable portion
that is an electrical package that goes underneath the skin behind the ear and from that comes
an electrode array that has a number of electrodes along its length and that electrode array
is placed within the cochlea and the various different electrodes along that array can
stimulate different parts of the cochlea, so the picture I've got behind me shows you
a typical example of the implantable portion of a cochlear implant. This is the electrical
package that helps to process the sounds and then this is the electrode and along this
bit along the tip is a number of different electrodes in the array.
So, the second part of the cochlear implant is the processor and that's the external part
that you can take on and off. The slide here demonstrates a typical example of a processor
which basically looks like a big hearing aid, it's got the battery and then the processor
itself and then a hook that allows it to stay on the ear and then there's a wire that communicates
with a coil and that coil has a magnet in it and that magnet keeps it in place and allows
it to communicate with the internal portion of the implant.
The implant itself basically picks up sounds through the processor, those are then sent
through to the internal portion and the sounds are divided up into different frequency bands
and each different frequency is sent to different frequency electrodes within the cochlea and
those electrodes then go on to stimulate the cochlear nerve and that then gives the patient
the sensation of sound.
The sound that you get from a cochlear implant is slightly different to natural sound, certainly
at the beginning it sounds quite electronic and some people describe it as sounding a
little bit like Mickey Mouse, but as time goes by, perhaps over the first three months
of use, the cochlear implant starts to sound much more natural and particularly in children
that are implanted at a very young age the hearing sounds almost like normal hearing
for day-to-day sounds like speech and environmental sounds, where it has slight limitation is
with music because music is much more complicated and the electronics within the processor of
the implant isn't capable of processing the complexity of music, so often people say that
the quality of music isn't very good through a cochlear implant.
A hearing aid essentially amplifies the patient's own hearing whereas a cochlear implant electrically
stimulates the hearing pathways of the brain and that's the main difference between the
two. There are two main groups of patients that
get cochlear implants, there's children that are born with profound deafness and then there
are adults that have developed speech and had normal hearing and then develop deafness
later on in life and those two groups are quite different with the children who are
born with profound deafness, it's really important that they're implanted before the age of about
four or five because if they don't get auditory stimulation then the brain isn't able to use
sounds that it receives if they're implanted beyond the age of four or five. In the adults
that are implanted after they've achieved speech or developed normal speech, then they
can be implanted at any age essentially even ten or twenty years after the development
of the profound deafness.
Hearing isn't quite restored back to normal with a cochlear implant, there are several
different elements to hearing, understanding speech is probably the most important element
and if you were able to score hearing from 0 to 100, somebody that's profoundly deaf
would score 0 and somebody with normal hearing would score 100, then a cochlear implant user
on average would score about 70% or 80% in a quiet environment. Where they might struggle
a little bit more is in a noisy environment and the average score probably in noise is
around 60% to 70%.
The other element of hearing is the ability to hear where sounds are coming from and you
can achieve that with cochlear implants if you have two implants, one in each ear. If
you only implant one ear, then you won't have that ability to identify where sounds are
coming from. In the UK in adults, we are only able to implant one ear but in children we
are able to implant both ears so for children they should be able to develop normal ability
to identify where sounds are coming from. So, the main advantage of a cochlear implant
is that you go from not being able to hear anything to being able to hear fairly normally
and function in everyday life, so you can work normally, enjoy social activities normally.
Where they slightly compromise is with music appreciation and there are obviously some
inconveniences to having had a cochlear implant so you have to wear the external processor
in order to get the benefit from the implant and that has some connotations from a cosmetic
perspective, you can only hear when you're wearing it, so if you go swimming for example
you might want to take the implant off and you won't be able to hear. There are actually
new types of implant currently being developed to get around those issues and I don't think
it will be long before we've got fully implantable cochlear implants that will allow people to
hear even in the night or when they're swimming and there are also other developments, so
most of the cochlear implant companies now have waterproof covers for the external processor
so actually you can swim with the device if you want to.