The imaging tool optical coherence tomography (OCT), routinely used to diagnose and plan treatment for eye diseases, has been modified to collect images of and measure fluid levels in the inner ear.
Researchers from the Keck School of Medicine of the University of Southern California (USC) in the US adapted the method developed for ophthalmology and used it to visualise tiny structures in the inner ear.
Their proof-of-concept study found the imaging can measure fluid levels in the inner ear, which correlate with a patient’s degree of hearing loss.
Their team tested the new tool in 19 patients undergoing ear surgery for various conditions. They found OCT could reliably detect fluid imbalance in the inner ear, which was correlated with the severity of a patient’s hearing loss.
Although the tool is limited to use during surgery, the researchers are working to adapt it for application in the clinic and said it may be able to improve diagnosis and treatment of hearing loss.
OCT uses light waves to scan tissue and create 3D images, similar to the way ultrasound produces images using sound waves.
They published their findings in Science Translational Medicine on 23 July 2025.
“These findings are exciting because hearing loss can happen very suddenly, and we often don’t know why,” said senior author, Professor John Oghalai. “OCT offers a way to explore the underlying cause and potentially guide treatment.”
Professor Oghalai is professor and chair in the Caruso Department of Otolaryngology – Head and Neck Surgery and the Leon J. Tiber and David S. Alpert Chair in Medicine at the Keck School of Medicine.
Sudden hearing loss, sometimes accompanied by vertigo, happens in Ménière’s disease, cochlear hydrops and other ear conditions. One hallmark of these diseases is an imbalance of fluids in the inner ear, but measuring fluid balance is a challenge, he said. The best available technology, magnetic resonance imaging (MRI), lacks the resolution needed to reliably diagnose or guide treatment, he added.
OCT offers a quicker, more accurate and less expensive way to see inner ear fluids, hair cells and other structures relevant to diagnosing and treating hearing loss, Prof Oghalai said.
With funding from USC and the National Institutes of Health, he joined with Professor Brian Appelgate, professor of otolaryngology – head and neck surgery, and ophthalmology at the medical school, and biomedical engineering and electrical and computer engineering at USC Viterbi School of Engineering.
The findings build on the team’s earlier work where they used OCT to collect images of the cochlea in awake animals for the first time.
With improvements, the tool could help clinicians more quickly find the cause of hearing loss, determine how to treat it, and even support efforts to develop new therapies to restore hearing, Prof Oghalai said.
Measuring fluid balance
Six patients in whom the tool scanned the inner had normal inner ear function, four had Ménière’s disease, and nine had vestibular schwannoma.
During surgery, the mastoid was temporarily removed, allowing researchers to use OCT to collect images of the fluid compartments in the inner ear.
OCT images found patients with Ménière’s disease or vestibular schwannoma had higher levels of endolymph fluid, compared with those with normal inner ear function.
Increased endolymph levels were linked to greater hearing loss, indicating that measuring these fluid levels could help predict the severity of symptoms.
“We’ve known for a long time that endolymph is related to hearing loss, but until now, measuring it in a living patient has been a major challenge,” Prof Oghalai said.
He said OCT could help surgeons, including by helping to avoid damage to delicate ear structures and distinguishing brain tumours from healthy tissue. The researchers are working to develop a smaller, more affordable version of the tool that they plan to distribute and test with surgeons.
OCT could benefit many more people if it could be used to collect images of the inner ear while patients are awake in the clinic, he said.
Developing a clinic tool
To achieve this goal, the team has received funding and are working to improve the software and image-processing techniques to obtain clear images from patients without removing the mastoid bone.
OCT could offer major benefits over MRI because it is less expensive, faster and can be done back-to-back to test treatment effectiveness, Prof Oghalai said.
For example, a provider could collect an image, give medication treatment for a fluid imbalance, then take another image 30 minutes later.
“Patient symptoms – sensations of hearing loss, pressure in the ear, or vertigo – can be affected by many unrelated factors such as mood, stress, nasal congestion and allergies,” he said.
“However, inner ear fluid levels reliably assess what is going on inside the inner ear. We have lots of treatment options available, but it often takes many weeks to figure out what works for a given patient. This could be a faster way to help.”
If OCT could be used outside the operating room, it may also support development of new treatments for hearing loss, he added. Several gene therapies, which aim to regenerate lost hair cells in the inner ear, are in clinical trials. OCT may provide a fast and precise way to test the effectiveness of such therapies by collecting images of hair cells as they grow.
“OCT helped researchers develop treatments for retinal diseases, including macular degeneration, so we’re hoping it can have a similar impact for hearing loss,” Prof Oghalai said.
*Professors Oghalai and Applegate are founders of AO technologies, whose goal is to translate inner ear imaging technologies for clinical purposes. It is directly related to this work.
More reading
Grant for OCT imaging of the cochlea to better understand ear conditions’ pathology
Study finds new OCT otoscope enhances diagnosis of ear disease
Researchers discover how the inner ear is formed
