These two categories of devices serve the needs for most hearing-impaired patients. However, some patients have special situations or conditions that prevent them from being ideal candidates for either hearing aids or cochlear implants, or they may simply desire better sound quality, performance, or convenience than they are getting from their conventional hearing aids. For these patients, there are several other types of devices which are grouped together under the heading of “implantable hearing devices” because they all require some type of procedure to place the device (like a cochlear implant) or are worn inside the ear.
Bone-Conduction Hearing Devices
Sound travels through bone very efficiently. This is why a tuning fork placed anywhere on the head can be heard well in the better hearing of the patient’s ears. This is the idea behind bone-anchored hearing devices. They are devices which attach to a small titanium (metal) pedestal which is surgically placed into the bone behind the ear. The pedestal sticks out slightly and the hearing aid snaps onto it, making it easily removable. These devices are appropriate for patients with conductive losses and bone conduction scores on their audiogram of 60 decibels or better (numerically lower), but for whom conventional hearing aids are not suitable. The procedure to place the pedestal is done at the Shea Clinic outpatient surgery center and generally takes 30 minutes or less. The two commonly placed devices in the category are the Ponto (Oticon Corporation) and the BAHA Connect (Cochlear Corporation). The BAHA Attract (Cochlear Corporation) is similar but attaches via a magnet, so there is not pedestal protruding through the skin. These devices are also FDA approved for patients with single-sided deafness (deaf in one ear but good hearing in the other).
A newer type of hybrid bone-conduction device combines a surgically implanted receiver which delivers vibration or energy directly to the bone, while the processor is worn on the outside of the head behind the ear and attaches via a magnet, like a cochlear implant processor. Examples of this type of device are the BONEBRIDGE (Med-El Corporation) and the Osia (Cochlear Corporation).
Vibrant Soundbridge (Med-El Corporation)
This device also uses an implanted portion, which is surgically placed under the skin behind the ear, and an external processor which attaches via a magnet. Sound energy is converted into electrical signals by the processor and sent across the skin to the internal component which has an electrode (wire) that leads into the middle ear. At the end of the electrode is the Floating Mass Transducer, which vibrates in response to the signals, and which is attached to the tiny bones in the middle ear. This type of system directly drives the inner ear by feeding mechanical energy into the middle ear bones. It is appropriate for moderate sensorineural hearing loss, conductive, or mixed hearing losses.
Earlens
The Earlens is a type of hearing aid system that uses a “lens” to drive the ear drum instead of amplified sound like a conventional hearing aid. This lens is a tiny device that is attached to the ear drum by an otologist (ear surgeon) via a minor procedure. The processor is worn on the ear like a hearing aid. It collects sound and converts it into laser light energy, which is then directed at the lens, which in turn converts this energy into vibrations to drive the ear drum. The Earlens is said to provide significantly improved sound quality and bandwidth when compared to conventional hearing aids.
Maxum (Ototronix Corporation)
The Maxum is a semi-implantable minimally invasive device which also drives the ossicular chain (tiny bones in the middle ear), but instead uses a processor worn in the ear canal like a hearing aid that directs electromagnetic energy through the ear drum to a magnetic titanium implant that is surgically attached to the ossicular chain. It provides sound quality superior to conventional hearing aids.
Envoy Esteem
The Esteem is the only fully implantable hearing system. Once it is surgically placed, there are no external components on the outside of the head or in the ear canal. The system uses the ear drum as a microphone which drives a sensor that converts the vibrations into electrical signals that are then sent to a processor. The processor amplifies the signals and sends them to a driver which is attached to the stapes (stirrup-shaped middle ear bone in contact with the inner ear), thus driving the inner ear. The battery is contained in the processor and requires replacement every few years via a surgical procedure. The Esteem is FDA approved for moderate to severe sensorineural hearing losses that are not severe enough for a cochlear implant.
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