anchored hearing aids (BAHA)
hearing aids (vibrant sound
1) Conventional hearing aids
A hearing aid is a device to amplify sounds reaching the ear.
Consists of 3 parts :
Microphone: picks up sound & converts them to electrical
Amplifier: magnifies electrical
Receiver: converts electrical
impulses back to sound.
This amplified sound is then carried through
the earmould to the tympanic membrane.
Types of Hearing Aids
Air conduction hearing aid- the amplified sound is
transmitted via the ear canal to the tympanic
Most of the aids are air conduction type.
They can be of 5 types.
Body-worn types: most common; microphone and
amplifier along with the battery are in one case worn at
the chest level while receiver is situated at the ear
allows high degree of amplification.
useful in severely deaf persons or children with
Behind-the-ear (BTE) types: microphone, amplifier
receiver and battery are all in one unit which is worn
behind the ear.
It is coupled to the ear canal with a tubing and an
useful for slight to moderate cases of hearing loss.
Spectacles types: it is a modification of “behind-theear” type & the unit is housed in the auricular part of
the spectacle frame.
useful to persons who need both eye glasses for vision
and a hearing aid.
In-the-ear (ITE) types: The entire hearing aid is
housed in an earmould which can be worn in the ear.
useful in mild to moderate hearing loss.
very popular because of their cosmetic appeal.
Canal types (ITC & CIC): The hearing aid is so small
that the entire aid can be worn in the ear canal without
projecting into the concha.
For using this aid, it is required that the ear canal
should be large and wide and the patient should have
dexterity to manipulate the minute controls in the aid.
useful in mild to moderate hearing loss.
2 types available- in the canal (ITC) &still smaller and
invisible type, completely in the canal (CIC).
Bone conduction hearing aidinstead of a receiver, it has a bone vibrator which
snugly fits on the mastoid & directly stimulates the
useful in persons with actively draining ears, otitis
externa or atresia of the ear canal when ear-inserts
cannot be worn.
Indications for Hearing Aid
Any individual who has a hearing problem that
cannot be helped by medical or surgical
means is a candidate of hearing aid.
Fitting a Hearing Aid
Consideration is given to :
Degree of hearing loss
Configuration of hearing loss (type of frequencies
Type of hearing loss (conductive or sensorineural)
Presence of recruitment
Uncomfortable loudness level
Age & dexterity of patient
Condition of the outer and middle ear
Cosmetic acceptance of the aid
Type of earmould
The type of fitting; whether it is monoaural (one aid
only), binaural (one aid for each ear), binaural with yconnection (one aid but two receivers, one for each
ear) or the CROS type.
CROS (contralateral routing of signals) –
microphone is fitted on the side of the deaf ear and the
sound thus picked up is passed to the receiver placed
in the better ear.
This is useful for persons with one ear severely
impaired & helps in sound localisation coming from the
side of the deaf ear.
Now bone-anchored hearing aids (BAHA) are being
preferred for single-sided deafness & have replaced
the use of CROS aids.
2) Bone-anchored Hearing Aids
Based on the principle of bone conduction.
Has 3 components:
The titanium fixture is surgically embedded in the
skull bone with abutment exposed outside the skin.
The titanium fixture bonds with the surrounding
tissue in a process called osseointegration.
The sound processor is attached to the abutment
once osseointegration is complete which usually
takes 2 to 6 months after implantation.
Indications for BAHA
when air-conduction hearing aid cannot be used.
- canal atresia, congenital or acquired, not amenable
- c/c ear discharge, not amenable to trtmnt
- excessive feedback & discomfort from airconduction hearing aid.
Conductive or mixed hearing loss, e.g. otosclerosis &
tympanosclerosis where surgery is contraindicated.
Single-sided hearing loss
BAHA have replaced the use of CROS aids.
The BAHA device can be implanted on the side of
deaf ear, and it transmits the sound by means of bone
conduction to the contralateral cochlea.
The BAHA is fixed on the deaf side & collects sound
waves to transmit to healthy cochlea of the other side.
This process eliminates the head-shadow effect and
allows for hearing from both sides of the head
typically performed in a single stage in adults.
Abt 3 months are allowed for osseointegration bfr the
sound processor can be attached.
2 stage procedure is recommended in children in
whom the fixture is placed into the bone in the first
stage. After abt 6 months to allow for osseointegration,
a second stage operation is done to connect the
abutment through the skin to the fixture.
Failure to osseointegrate the implant
local infections and inflammation at the implant site.
3) Implantable Hearing Aids
Works on a direct drive principle.
Rather than delivering acoustic energy into the
external auditory canal (as with traditional hearing aid
systems), direct drive middle ear implant systems use
mechanical vibrations delivered directly to the
ossicular chain, while leaving the ear canal open.
Implantable middle ear devices are generally available
in 2 types :
Piezoelectric devices: operates by passing an
electric current into a piezoceramic crystal, which
changes its volume and thereby produce a vibratory
signal. This piezoelectric transducer in turn is coupled
to the ossicles and drives the ossicular chain by
Electromagnetic hearing devices: function by
passing an electric current into a coil, which creates a
magnetic flux that drives an adjacent magnet. The
small magnet is attached to one of the ossicles of the
middle ear to convey vibrations to the cochlea.
Vibrant soundbridge device
2 components – internal & external
The internal component is called VORP (Vibrating
Ossicular Prosthesis) and is made up of 3 partsreceiver, FMT (Floating Mass Transducer) and a
conductor link between the two.
The external component is called the audio
processor which is worn behind the ear. It contains a
microphone that picks up sound from the environment
and transmits it across the skin by radiofrequency
waves to the internal receiver.
Adults aged 18 yrs and older with moderate to severe
sensorineural hearing loss.
Candidates should have experience of using traditional
hearing aids and should have a desire for an
alternative hearing system.
The internal device is surgically implanted.
Conducted under general anaesthesia.
The receiver of the implant is positioned under the skin
over the mastoid bone via a std cortical
mastoidectomy and posterior tymapanotomy
The ossicular chain is visualised and the FMT is
attached to the long process of incus.
6 to 8 weeks after the procedure, the patient is fitted
with the external audio processor.
A direct drive system provides mechanical energy
directly to the ossicles, bypassing the ear canal and
the tympanic membrane.
Eliminates occlusion, feedback, discomfort and wax
Provide improved sound quality to the hearingimpaired subjects.
Disadvantages of conventional hearing aids
Cosmetically unacceptable due to visibility
Occlusion of external auditory canal
Collection of wax in the canal and blockage of insert
Sensitivity of canal skin to earmoulds
Problem to use in discharging ears
1) Cochlear implants
Electronic device that can provide useful hearing and
improved communication abilities for persons who
have severe to profound hearing loss and who cannot
benefit from hearing aids.
Works by producing meaningful electrical stimulation
of the auditory nerve.
External component: consists of an external speech
processor and a transmitter.
Internal component: it is surgically implanted and
comprises the receiver/stimulator package with an
Used both in children and adults.
Bilateral severe to profound sensorineural hearing
Little or no benefit from hearing aids.
No medical contraindication for surgery
Good family & social support toward habilitation
Adequate cognitive function to be able to use the
Outcomes of cochlear implantation
Factors that predict a successful clinical outcome are :
Previous auditory experience (post-lingual pts or prior
use of hearing aids)
Younger age at implantation ( especially for pre-lingual
Shorter duration of deafness
Neural plasticity within the auditory system
Carried out under general anaesthesia
There are broadly 2 surgical techniques:
The facial recess approach where a simple cortical
mastoidectomy is done first & the short process of the incus and
the lateral semicircular canal are identified.
The facial recess is opened by performing a posterior
The stapes, promontory and round window are identified.
Cochleostomy is performed antero-inferior to the round window
membrane to a diameter of 1 to 1.6 mm depending on the
ii) The pericanal technique where a tympanomeatal flap
is elevated to perform a cochleostomy either by
endaural or postaural approach.
a bony tunnel is drilled along the external canal
towards the middle ear.
Exposure of device and extrusion
Pain at the site of implant
Migration/displacement of device
Late device failure
2) Auditory Brainstem Implant (ABI)
Designed to stimulate cochlear nuclear complex in the
brainstem directly by placing the implant in the lateral
recess of the fourth ventricle.
Such implant is needed when CN VIII has been
severed in surgery of vestibular schwannoma.
ABI help in communication, awareness and
recognition of environmental sounds; however they
are not efficient as multichannel cochlear implants.