Hidden Hearing Loss and Its Connection to Tinnitus and Hyperacusis
Hidden hearing loss is different from typical hearing loss.
It doesn’t show up on a standard audiogram, since that test only measures the
softest sounds a person can hear — essentially how sensitive the cochlear hair
cells are — but it doesn’t tell us much about how clearly we hear or how well
we understand speech in complex environments.
This condition, which currently has no known cure, was first
described in 2009 by Drs. Sharon Kujawa and Charles Liberman. Their research
showed that some people had difficulty understanding speech in noisy
environments — like parties or busy restaurants — even though their audiograms
were normal. What they discovered was that the issue was not in the hair cells
of the cochlea, but in the auditory nerve. Specifically, the synapses — the
connections between the hair cells and the nerve — were damaged. This meant
that although sound entered the ear, the information wasn’t being properly
transmitted to the brain. This form of hearing damage was later called cochlear
synaptopathy, and it’s often caused by exposure to loud sounds, as well as
aging. Other potential causes include ototoxic medications or autoimmune
conditions.
In 2015, a study led by Dr. Stéphane Maison also found that
underuse of the ears — due to lack of sound exposure for any number of reasons
— could also lead to cochlear synaptopathy.
The discovery of hidden hearing loss in people who have
normal audiograms has given further weight to a popular theory: that when the
brain doesn’t receive the expected amount of auditory input, it tries to
compensate by creating a phantom sound — what we know as tinnitus. This might
help explain cases where people have both tinnitus and hyperacusis, yet their
hearing tests come back as normal (or even above average for their age). Still,
it’s important to note that not all people with tinnitus or hyperacusis and
normal hearing test results necessarily have hidden hearing loss.
One possible way to identify hidden hearing loss is by
testing how well someone can understand speech in noisy environments.
Researchers are working on developing better diagnostic tools for this purpose,
including tests based on otoacoustic emissions. Interestingly, a recent study
(2023) found that eye movement tracking could be another method for early
detection. Reduced eye movement while trying to follow a conversation in a
noisy setting may be a sign of hidden hearing loss and related auditory difficulties.
Sources:
- https://hearinghealthfoundation.org/blogs/tackling-hidden-hearing-loss
- https://www.facebook.com/reel/709272184552817
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