How to Choose the Right Size Dome for Openfit Hearing Devices

Why the Dome Size Changes Everything in the Openfit Experience

Is very common that a person receives the hearing device, the audiologist applies the standard dome, and the patient goes home with the sensation that something does not result perfectly correct. The sound arrives, yes, but there is a whistling, or the voice of the interlocutor seems distant, or the device feels unstable in the ear. In the majority of the cases, the problem is not the device. The problem is the dome.

The dome is that small piece of silicone that sits at the end of the receiver wire and positions itself inside the ear canal. In the openfit configuration, the dome has the precise function of maintaining the canal partially open, permitting to the natural low frequencies to pass without amplification while the device manages the high frequencies. But if the size is wrong, all the acoustic balance collapses.

A dome too small leaves excessive space around it: the amplified sound escapes from the canal and returns toward the microphone of the device, creating the known feedback whistle. A dome too large, instead, closes the canal more than necessary, transforms the openfit into a closed fit, and the patient perceives the own voice as if speaking inside a bottle. This phenomenon, that in audiology is called occlusion effect, is one of the principal reasons for which many persons abandon the device in the first weeks.

For this reason, choosing the correct size is not a secondary detail. Is the fundamental passage that determines if the openfit will result comfortable and effective, or if it will remain in the drawer after three days.

The Three Measurements That Matter and How to Obtain Them

For what regards the selection of the dome, there exist three parameters that must be considered together:

• The diameter of the ear canal. The audiologist measures it during the fitting with an otoscope or a video-otoscope. The canal is not a perfect cylinder: has an oval section, narrows toward the second curve. The dome must accommodate in the first portion of the canal without forcing.
• The depth of insertion. This indicates how far the dome enters before it rests gently against the walls. A dome that enters too much touches the sensitive zone of the canal and provokes irritation. A dome that stays too superficial does not create sufficient acoustic seal for the mid frequencies.
• The degree of the hearing loss. This is the parameter that many persons ignore. The openfit is indicated generally for losses that are mild to moderate in the high frequencies, with low frequencies still preserved. If the loss in the low frequencies is more elevated than 40 decibels, the openfit with a small dome will not provide sufficient gain, and a more closed configuration becomes necessary.

The audiologist should always verify these three elements before applying the dome. But is also important that the patient communicates the own sensations in the first days, because the ear canal changes shape slightly with the movement of the jaw, with the temperature, with the humidity of the season.

Small, Medium, Large: What Each Size Does to the Sound

The manufacturers provide normally three or four sizes of dome. Here is a practical reference for understanding the differences:

Is necessary to understand that passing from one size to the other changes not only the physical comfort but the entire frequency response. The medium dome, for example, maintains open the canal enough to let pass the natural resonance around 2700 hertz, while the large dome begins to attenuate this zone. The patient who passes from medium to large without a proper re-programming of the device will notice the sound “flat” and “closed.”

The Common Errors That Compromise the Result

In the practice, there are errors that repeat with frequency and that is important to recognise:

• Choosing the dome only on the basis of the comfort sensation in the first ten seconds. The canal needs between twenty and thirty minutes for adapting. A dome that seems slightly tight in the first moment often results perfect after the adaptation period.
• Using always the same size for both ears. The two canals are not identical. In many persons, one ear accepts a medium and the other needs a small. This is normal and must be respected.
• Not replacing the dome when the silicone becomes rigid or discoloured. The material loses elasticity after approximately three months of daily use, and the seal diminishes without that the patient notices immediately.
• Ignoring the accumulation of cerumen on the dome. Even a small quantity of wax on the exit holes of an open dome modifies the ventilation and introduces distortion. The cleaning must be made every evening with a dry cloth, never with water or alcohol that degrade the silicone.

When to Change the Dome: The Signs the Body Gives You

The ear communicates very clearly when the dome is not correct. Is sufficient to listen to these signals:

• A persistent whistle when moving the jaw or when smiling indicates that the dome is too small and the sound escapes.
• The sensation of the own voice that resounds, as speaking in a small room, indicates that the dome is too large and is creating occlusion.
• An itching or a light pain after two hours of use suggests that the dome is pressing against a point of the canal where the skin is more thin.
• The perception that in a noisy environment the voices disappear more than before the fitting can signal an excessive ventilation: the dome is too open for the degree of the loss.

When one of these signs presents itself, is not necessary to suffer for weeks waiting that “the ear will adapt.” Is better to return from the audiologist and request a different size. The adjustment is immediate and does not require new programming of the device in the majority of the cases.

Supporting the Hearing Health Beyond the Device

The openfit device resolves the mechanical problem of the amplification, but the health of the auditory system depends also on the general condition of the inner ear, of the microcirculation, of the nervous structures that elaborate the sound. Many audiologists, in my experience, remind to the patients that the device is an aid, not a substitute for the care of the hearing organ.

For this reason, there is a growing attention toward the nutritional support of the auditory function. In this context, I have read with interest the information presented on acuvit.health where is explained how certain nutrients can sustain the cells of the cochlea and the vascularisation of the inner ear. The approach is not to substitute the device with a supplement, obviously, but to consider the hearing health in a more complete vision.

The product Acuvit, for example, is formulated as a complementary support for persons who already use hearing devices and want to maintain the auditory structures in the best possible condition. The logic is simple: if the dome brings the sound correctly to the tympanic membrane and the ossicles, the inner ear must be in good metabolic state for transforming that sound into nervous signal. The two things work together, not one without the other.

Is a perspective that I find very sensible, because treats the hearing not as a mechanical problem isolated but as a function of the whole organism.

Final Practical Advice for the Fitting Day

For the person who must choose the dome for the first time, or who is not satisfied with the current one, here are the steps that make the difference:

• Ask the audiologist to try at least two sizes in each ear during the same appointment. Do not accept the first application without a comparison.
• Wear the test dome for at least twenty minutes in the clinic before deciding. Walk, talk, move the jaw.
• Request that the audiologist verifies the real-ear measurement with the specific dome applied, not with a generic one.
• Schedule a control after two weeks of daily use, because the perception changes with the habit.
• Keep at home a spare set of domes in the same size and in the adjacent size, so that if the sensation changes with the season or with a light inflammation, is possible to adjust immediately.

The right dome is not the one that the manufacturer considers “standard.” Is the one that disappears from the perception of the person who wears it, that permits to forget the device and to remain present in the conversation. When this happens, the openfit has reached its true purpose.