July 23, 2014
The vast majority of patients seen for hearing loss present with roughly the same hearing in each ear. Symmetric hearing is expected in typical cases related to aging, noise exposure, toxicity, heredity and many disease processes. Noise exposure may affect one ear to a greater extent if a constant source of occupational or recreational sounds is located closer to that ear, as in various machinery, firearms, musical instruments, etc. Significant asymmetry, however, is never taken lightly, and such patients are encouraged to be evaluated medically. This may be a “red flag” for diseases of the ear or “retrocochlear” conditions affecting the hearing nerve leading toward the brain. Many of these conditions can produce associated symptoms, such as dizziness/imbalance and/or tinnitus.
Occasionally we will see a patient with normal hearing in one ear and significant loss in the other. One ear needs no help to hear, while the other is in need of amplification or perhaps is a total loss. This condition is very often left untreated by the patient. Obviously, one ear is pulling in as much sound as possible, however, the other ear is depriving the listener of half the sound of the world. What are some consequences for non-treatment, and what are the options for these patients?
For more significant asymmetric losses, localization of sounds becomes very difficult. The brain is wired to receive input from both sides and to locate sounds based on the loudness difference between the ears, as well as the time difference. Sounds are assumed to be more intense or heard sooner in the ear closer to the source. The brain is also thought to be responsible for listening in the presence of background noise. This ability is thwarted by hearing asymmetry, as input from both ears is needed for this function. Additionally, the brain can squelch echoes in somewhat in reverberant rooms, but needs two good ears to do so. These consequences can be summarized by stating that single-sided hearing is effective only in quiet spaces with good acoustics and preferably when using eye contact.
Several options for treatment are available. If the poorer ear is near-normal, the patient may opt to wait until the hearing decreases to a more significant level. With greater losses, a hearing aid on the poor side is often extremely helpful for increasing hearing, improving communication and restoring sound localization. In the case of profound or even total loss of hearing, often known as “single sided deafness”, a traditional high-powered hearing aid may not suffice. One option is a CROS (contralateral routing of sound) instrument that places a microphone on the poor side and transmits the sound to the functional ear. Patients eventually learn to differentiate sounds from each side, even if they are being perceived in the same ear.
We should neither underestimate the importance of hearing from both ears, nor fail to recognize the importance of a correct diagnosis and follow-through. It begins with a single appointment for thorough diagnostic testing and continues as a collaboration between an educated patient and a professional. Let us put you on a clear path to good hearing and health.
