OBJECTIVE:Assessment of human vocal fold (VF) morphology and vibration is largely limited to surface visualization via laryngeal videostroboscopy. Using optical coherence tomography (OCT), this study aims to measure VF vibratory dynamics in the coronal plane of healthy volunteers to support a quantitative assessment of VF biomechanics. STUDY DESIGN:Cross-sectional observational pilot study METHODS: Twelve healthy participants underwent awake, transoral imaging using a custom-built, hand-held rigid laryngoscope equipped with OCT technology. Phonation was captured during sustained vowel /i/ production at a modal pitch and loudness. A novel algorithm was utilized to reconstruct the phase-resolved VF vibratory cycle during phonation from the OCT data. Seven dynamic metrics were extracted from each video reconstruction, including closed quotient (CQ), angle at closure (AaC), divergent phase vertical thickness (DPVT), closed phase vertical span (CPVS), mucosal peak, amplitude of lateral excursion (amplitude), and vertical phase difference (VPD). Data were grouped by gender, and applicable metrics were stratified into right vocal fold and left vocal fold regions. Independent t-tests were performed to assess gender and laterality differences for each metric. Pairwise Bonferroni-adjusted Pearson correlations were performed between metrics. RESULTS:Seven novel metrics were successfully extracted and measured from OCT data in all subjects. Significant gender differences were found for DPVT (p = 0.015), amplitude (p = 0.049), and VPD (p = 0.043). No significant laterality differences were observed except for DPVT in the female group. Correlation analyses showed a positive correlation between DPVT and CPVS (r = +0.89). CQ was negatively correlated with AaC (r = -0.74) and positively correlated with VPD (r = +0.83) CONCLUSION: OCT imaging of the VFs can be successfully performed in normal subjects during phonation to visualize sub-surface VF anatomy and vibration, enabling quantitative characterization of VF dynamics.

PURPOSE OF REVIEW:Optical coherence tomography (OCT) is a noninvasive optical imaging technique to image soft tissue and thin bony structures with high resolution, approaching that of histology. This review summarizes recent progress in the clinical application of OCT for tympanic membrane and middle ear disease. RECENT FINDINGS:Recent reports from clinical trials show that OCT is having a meaningful impact on the diagnosis of fluid in the middle ear. In parallel with this, numerous groups are obtaining previously unattainable normative data in vivo on human middle ear structures. OCT is also starting to be used for functional assessments of the middle ear in the clinical setting by detecting sound and pressure-evoked motion. SUMMARY:OCT allows real-time noninvasive radiation-free structural and functional imaging of the tympanic membrane and middle ear at the point of care. As artificial intelligence becomes more commonplace in medicine, it is likely that OCT will become a key technology for the otolaryngologist. The data provided by OCT can be used to train machine learning algorithms for the segmentation of ear structures, which will ultimately support the automated diagnosis of ear disease. This will also aid in objectively tracking disease progression over time. Thus, OCT presents much promise for our field by revolutionizing office-based otological diagnostics.

Significance:Cholesteatomas, benign tumors that grow in the middle ear, can lead to conductive hearing loss. If not completely removed during surgery, these tumors may regrow. Current imaging technologies struggle to detect residual tumors noninvasively due to limitations in contrast and resolution, often necessitating additional surgery for inspection. To address this, we developed a catheter endoscope capable of being inserted through the Eustachian tube, allowing detailed examination of the middle ear without surgery. Using two-photon polymerization (2PP) technology, we fabricated miniature, side-viewing reflective endoscope objectives. This approach enabled the rapid production of single-element objectives with highly repeatable optical properties, easily adaptable to specific imaging needs. Aim:We aim to design, fabricate, and demonstrate a catheter endoscope for optical coherence tomography (OCT) endoscopy of the middle ear via the Eustachian tube. Approach:Side-viewing, reflective lenses were designed in OpticStudio and 3D printed using 2PP followed by sputter coating with gold. Standard metrology techniques were used to verify and optimize the objective's shape. The optical performance of the catheter endoscopes was measured with a beam profiler. Finally, OCT imaging of the middle ear of a pig via the Eustachian tube was completed using the fully assembled catheter endoscope. Results:Metrology showed the printed lenses conformed closely to the design. The catheter endoscope's FWHM spot size had a mean ± standard deviation of 25.3 ± 1.8    μ m with a measured working distance of 1.960 ± 0.057    mm . Volumetric OCT images of the middle ear, inner ear, and Eustachian tube were captured in a postmortem pig head using the catheter endoscope. Conclusions:The 2PP approach is fast and highly repeatable for miniature reflective objective fabrication. OCT catheter endoscopy via the Eustachian tube enabled imaging of the middle ear, Eustachian tube, and surprisingly part of the inner ear.

Significance:There is no clinical imaging method to visualize the soft tissues of the human cochlea, which are crucial for sound transduction and are damaged in sensorineural hearing loss. Although optical coherence tomography (OCT) has been effective in small animal models, we show for the first time that it can image through the full thickness of the ex-vivo human otic capsule and resolve cochlear microstructures despite increased scattering. Aim:We aim to investigate whether OCT could image the cochlea through the otic capsule. We compared 1.7 and 1.3    μ m OCT to test if the reduced scattering at 1.7    μ m provided any appreciable advantage for imaging the cochleae. Approach:OCT interferometers were built for both 1.3 and 1.7    μ m wavelengths, using identical sample and reference arm optics in both systems. Imaging was performed on two fixed human temporal bones with intact cochleae. The interferometers were designed to allow seamless switching between 1.3 and 1.7    μ m OCT without disrupting the temporal bone during imaging. Results:We took volumetric OCT images at the base, apex, and hook regions of fixed ex-vivo human cochleae and compared the images taken at 1.3    μ m with those taken at 1.7    μ m . At both wavelengths, we could see through the otic capsule and identify cochlear structures. In some cases, 1.7    μ m OCT resulted in clearer images of the lateral wall, interior scala, and fine cochlear structures due to reduced multiple scattering at depth compared with 1.3    μ m . Conclusions:We conclude that both 1.7    μ m and 1.3    μ m OCT can image through the human otic capsule, offering the potential for direct measurement of cochlear vibrometry or blood flow in living humans. Using 1.7    μ m light, we observed reduced multiple scattering in the otic capsule, leading to enhanced contrast of cochlear structures compared with 1.3    μ m . However, these improvements were marginal and came with trade-offs.

Significance:Early detection of ear pathology is essential for preventing hearing loss, yet the sensitivity of otoscopic examinations by primary care providers during annual physicals remains low. Optical coherence tomography (OCT) offers a promising alternative for detailed imaging of the tympanic membrane (TM) and middle ear (ME), providing the potential for early identification of ear disease. Aim:We aim to develop a quantitative method for assessing symmetry between the right and left ears and to establish a baseline for this approach in normal subjects. Approach:Volumetric OCT images were acquired from 12 normal subjects using a custom hand-held OCT otoscope. A volume registration and fusion method was applied to expand the TM field of view, followed by TM thickness measurement and generation of 3D thickness maps. The symmetry between left and right TMs was quantitatively analyzed using the Dice similarity coefficient. Results:The average TM thickness was measured as 73.89 ± 14.79    μ m for left ears and 70.72 ± 11.58    μ m for right ears, with no statistically significant difference at the 0.05 level. The symmetry analysis revealed a mean similarity coefficient of 0.79 ± 0.02 between left and right ears among the 12 normal subjects. Conclusions:OCT imaging enables quantitative assessment of TM thickness and symmetry, offering a baseline for identifying early ear pathologies.

Snapshot spectrometers capture spatial and spectral data in real-time, offering transformative potential in biomedical imaging and environmental monitoring. However, conventional designs struggle to reconcile high spatial-spectral sampling density with device miniaturization. To address this, we present a compact snapshot imaging spectrometer leveraging a densely packed 3D waveguide array fabricated via two-photon polymerization (2PP), an additive manufacturing technique that achieves submicron precision in complex geometries. The design features 26,000 straight waveguides in an angled end-face configuration, with a 4 µm pitch and 2.5 µm core size. By introducing a vertical layer height increment of 32 µm, the array facilitates spectral data distribution across 40 pixels. The compact structure, measuring 852 µm x 552 µm x 4093 µm, offers new opportunities for integrating snapshot spectroscopy into portable devices. The system's performance is evaluated through measurements of spectral resolution, crosstalk, and throughput. Validation using USAF resolution target imaging and the biological microscopic samples demonstrates its potential to deliver accurate and high-efficiency spectral data.

Background: Skull base tumors can extend into the temporal bone and occasionally even be visible through the tympanic membrane (TM) if they grow into the middle ear cavity. The differential diagnosis of a skull base mass is extensive and ranges from non-tumorous lesions like cholesteatoma to benign tumors like schwannoma and to malignant lesions like metastatic cancer. Optical coherence tomography (OCT) is a noninvasive imaging technique that can image tissue with high resolution in three dimensions, including through structures such as the TM and bone. OCT angiography is also able to assess tissue vascularity. We hypothesized that OCT could help shrink the differential diagnosis in clinic on the day of initial presentation. Specifically, we thought that OCT angiography could help distinguish between highly vascular skull base tumors such as glomus jugulare and other less vascular tumors and middle ear pathologies such as cholesteatoma and schwannoma. Objectives: We sought to determine whether OCT can image through the TM in clinic to distinguish a normal ear from an ear with a mass behind the tympanic membrane. Furthermore, we sought to assess whether OCT angiography can detect vascularity in these masses to help inform the diagnosis. Methods: We designed and built a custom handheld OCT system that can be used like an otoscope in clinic. It is based off a 200 kHz swept-source laser with a center wavelength of 1310 nm and a bandwidth of 39 nm. It provides a 33.4 μm axial and 38 μm lateral resolution. Cross-sectional images of the middle ear space, including OCT angiography, were captured in an academic neurotology clinic. Patients with normal ear exams, glomus tumors, cholesteatomas, and facial nerve schwannoma were imaged. Results: OCT images revealed key structures within the middle ear space, including the TM, ossicles (malleus and incudostapedial joint), chorda tympani, and cochlear promontory. OCT also identified middle ear pathology (using pixel intensity ratio in the middle ear normalized to the TM) when compared with patients with normal ear exams (mean 0.082, n = 6), in all patients with a glomus tumor (mean 0.620, n = 6, p < 0.001), cholesteatoma (mean 0.153, n = 4, p < 0.01), and facial nerve schwannoma (0.573, n = 1). OCT angiography revealed significant vascularity within glomus tumors (mean 1.881, n = 3), but minimal vascularity was found in normal ears (mean 0.615, n = 3, p < 0.05) and ears with cholesteatoma (mean 0.709, n = 3, p < 0.01), as expected. Conclusions: OCT is able to image through the TM and detect middle ear masses. OCT angiography correctly assesses the vascularity within these masses. Thus, OCT permits the clinician to have additional point-of-care data that can help make the correct diagnosis.

The mammalian cochlea receives efferent feedback from the brain. Many functions for this feedback have been hypothesized, including on short timescales, such as mediating attentional states, and long timescales, such as buffering acoustic trauma. Testing these hypotheses has been impeded by an inability to make direct measurements of efferent effects in awake animals. Here, we assessed the role of the medial olivocochlear (MOC) efferent nerve fibers on cochlear amplification by measuring organ of Corti vibratory responses to sound in both sexes of awake and anesthetized mice. We studied long-term effects by genetically ablating the efferents and/or afferents. Cochlear amplification increased with deafferentation using VGLUT3-/- mice, but only when the efferents were intact, associated with increased activity within OHCs and supporting cells. Removing both the afferents and the efferents using VGLUT3-/- Alpha9-/- mice did not cause this effect. To test for short-term effects, we recorded sound-evoked vibrations while using pupillometry to measure neuromodulatory brain state. We found no state dependence of cochlear amplification or of the auditory brainstem response. However, state dependence was apparent in the downstream inferior colliculus. Thus, MOC efferents upregulate cochlear amplification chronically with hearing loss, but not acutely with brain state fluctuations. This pathway may partially compensate for hearing loss while mediating associated symptoms, such as tinnitus and hyperacusis.

Hearing loss and vertigo occur when there is an imbalance between the two inner ear fluids, endolymph and perilymph. The inner ear is a small delicate structure encased in dense bone deep in the base of the skull, making it challenging to image with high resolution. Because the fluid chambers are so small, there is no reliable way to measure their balance in a living patient to guide therapy. Here, we translated the technology of optical coherence tomography (OCT) for use in the human inner ear. Peering through the otic capsule bone during mastoid surgery, we imaged the lateral and posterior semicircular canals of patients with Ménière’s disease or vestibular schwannoma and measured the endolymph-to-perilymph ratio. Compared with normal controls, both patient groups demonstrated increased endolymph and reduced perilymph, a disorder termed endolymphatic hydrops. OCT imaging demonstrated good repeatability for measuring the endolymph-to-perilymph ratio. Our data indicate that increased endolymph-to-perilymph ratios correlated with the degree of hearing loss. Thus, small yet meaningful changes in inner ear fluid balance are detectable with this approach with better resolution than gadolinium-enhanced 3 Tesla magnetic resonance imaging, the current gold standard clinical imaging modality. Our findings support the feasibility of imaging the human inner ear during surgical procedures with OCT and demonstrate the ability to detect endolymphatic hydrops. Moreover, this technique permits the measurement of the fluid chambers within the inner ear in real time during surgical procedures with adequate sensitivity to guide the management of complex but common ear diseases.

Significance:Our understanding of mechanotransduction in mammalian inner ears remains incomplete, in part due to imaging limitations: current systems cannot simultaneously provide high-resolution images needed for subcellular analysis and the deep focus required for structural mechanics. Optical coherence tomography (OCT) enables structural and vibrational imaging through the bone of the intact cochlea in models such as mice, supporting studies of cochlear mechanics in animals with functional hearing. However, capturing both cellular ( < 10 μ m ) and structural ( > 200 μ m ) details requires rapid switching between optical configurations with numerical apertures ranging from 0.13 to 0.8. A spectral-domain OCT system combined with two-photon fluorescence microscopy (TPM) and interchangeable objectives could overcome this challenge, enabling high-precision vibration and fluorescence imaging across multiple scales in a single experiment. Aim:We aim to develop an integrated OCT and two-photon microscope optimized for imaging the morphology and function of the cochlea. Approach:We integrated a custom SD-OCT/TPM system into an upright microscope with a high-precision stage for animal positioning. The system uses two tunable liquid lenses to form a beam expander, enabling dynamic adjustment of the beam diameter at the back aperture of each objective. This optimized light throughput and maintained a high signal-to-noise ratio (SNR) across all objectives. In addition, we automated optical adjustments to facilitate seamless imaging with a wide range of objectives. Results:For each objective, we measured the SNR difference between a beam expanded to match the largest back aperture and a beam adjusted to match the back aperture of the objective. Except for the 4 × objective, the measured SNR improvements closely matched theoretical predictions. Using four selected objectives spanning the required numerical aperture (NA) range, we successfully imaged excised murine cochlea samples, obtaining relevant structural information across scales. In living murine models, we used TPM to locate fluorescent outer hair cells and make vibrometry measurements through the round window membrane. We found that hair cells, the basilar membrane, and the reticular lamina moved in phase in response to a 70 kHz stimulus at 90 dB SPL, consistent with expected cochlear mechanics. Conclusions:Automation and optimization of the optical system enabled seamless multiscale imaging of the murine cochlea, providing high-quality morphological, functional, and two-photon fluorescence images. The dynamic adjustment of the beam diameter within the microscope was essential for maintaining high SNR across a wide range of numerical apertures.

Optical Coherence Tomography (OCT) has been used to characterize cochlear endolymphatic hydrops (ELH) with distention of Reissner's membrane in mice after noise exposure. Noise exposure has been correlated with vestibular dysfunction, so we hypothesized that noise exposure can lead to ELH in the vestibular system. Little work has been performed using OCT to image the membranous labyrinth in the lateral and posterior semicircular canals (SCCs). We show that OCT with 12.5 µm axial resolution and 13.2 µm lateral resolution can image the SCCs and delineate the membranous labyrinth in anesthetized mice. A high-resolution OCT system with 2.45 µm axial and 3.95 µm lateral resolution provides improved distinction between the endolymphatic and perilymphatic fluid spaces that enables quantification of the endolymph to perilymph (E/P) area ratio in the SCCs. The LSCC E/P ratio in noise exposed mice (5.16 ± 0.67, mean ± standard deviation, n = 12) is significantly increased (p = 0.0014, unpaired Student's t-test) compared to control mice (4.26 ± 0.41, n = 10). Similarly, the PSCC E/P ratio in noise exposed mice (4.92 ± 0.52, n = 12) is significantly increased (p = 3.65e-6, unpaired Student's t-test) compared to control mice (4.00 ± 0.37, n = 11). Furthermore, the PSCC and LSCC E/P ratios correlate significantly (R2 = 0.284, p = 0.0063, linear regression). These data demonstrate that noise exposure leads to increased E/P ratio, a measurement of ELH, in both the LSCC and PSCC in mice, and this corresponds to ELH present in the cochlea after noise exposure. Therefore, noise exposure leads to ELH in both the cochlea and the vestibular system, suggesting a pathway for noise exposure to cause vestibular dysfunction.

The human cochlea, which encapsulates the hearing organ, remains difficult to image using current medical tools due to its delicate structure and location behind dense bone. Optical coherence tomography (OCT) has become an essential technology for imaging cochlear morphology and function in animal models, offering high spatial and temporal resolution. Our previous work demonstrated OCT’s ability to image cochlear structures in mouse models and to measure sound-induced vibrations at a nanometer scale. Translating this approach to human patients, however, requires overcoming challenges such as accessing the cochlea non-invasively through the ear canal. We previously designed a hand-held OCT endoscope for this purpose, but the initial design and lack of a camera made it very difficult to use in a clinical setting. In this paper, we present a redesigned OCT endoscope to image the human cochlea that addresses these limitations by reducing its size, improving visibility, and incorporating a forward-looking fiber bundle and camera for better navigation. We validated the device using both an opal checkerboard target and a cadaver temporal bone, demonstrating the ability to navigate to the round window niche via the ear canal. These advancements allow for detailed, real-time imaging of cochlear structures and represent a step toward the clinical application of OCT for diagnosing and treating hearing disorders of the inner ear.

Advances in optical coherence tomography have improved diagnostic imaging for otologic pathologies. We investigated handheld OCT (HHOCT) otoscopic device's ability to quantitatively analyze the middle ear and provide valuable information for the management of middle ear pathologies. Cross-sectional cohort. Eleven healthy patients, 5 patients with unilateral pathology, 6 patients with retraction pockets, and 1 patient undergoing ossiculoplasty were imaged using HHOCT in the clinic. Middle ear distances and retraction pocket depth were calculated using OCT volumes and compared to those on CT and in literature. Partial ossicular replacement prosthesis length was calculated before surgery and compared to the length chosen by an expert otologist. Data were characterized using descriptive statistics and paired t -tests. Volumes were analyzed and postprocessed using Amira (Thermofisher Scientific, Waltham, MA) and Fiji (NIH). HHOCT could image and obtain quantitative measurements of the middle ear at the point of care with greater resolution and precision than traditional imaging modalities. Mean incus diameter on OCT was 0.728 ± 0.089 mm, in agreement with cadaver studies. Measured middle ear distances and retraction pocket depths were not statistically significantly different from those measured on CT. The predicted prosthesis size for the ossiculoplasty patient was 2.46 mm, closely matching the 2-mm length chosen by an expert otologist. OCT can provide reliable measurements of the tympanic membrane and middle ear structures not readily available through traditional imaging modalities. Pre- or intrasurgical measurements with OCT may be beneficial for guidance on size and placement of ossicular prosthetics and may improve hearing outcomes.

Novel therapeutic delivery systems and delivery methods to the inner ear are necessary to treat hearing loss and inner ear disorders. However, numerous barriers exist to therapeutic delivery into the bone-encased and immune-privileged environment of the inner ear and cochlea, which makes treating inner ear disorders challenging. Nanoparticles (NPs) are a type of therapeutic delivery system that can be engineered for multiple purposes, and posterior semicircular canal (PSCC) infusion is a method to directly deposit them into the cochlea. We sought to assess PSCC infusion of gold NPs into the cochlea, including the NPs’ distribution and effect on cochlear mechanics. We performed optical coherence tomography (OCT) imaging to monitor PSCC infusion of gold NPs into the cochlear chambers. OCT imaging demonstrated that the infusion specifically targeted the perilymphatic spaces within the cochlea. We assessed cochlear mechanics by using OCT vibrometry to measure sound-evoked movements of the basilar membrane. We found no changes in cochlear mechanics between measurements at baseline, after the PSCC canalostomy, immediately after the infusion, and 1 h after the infusion of gold NPs (p > 0.05, paired t-test). These findings validate the PSCC infusion approach for perfusing the cochlear perilymphatic space with a nanoparticle delivery system. Thus, PSCC infusion of nanoparticles is a feasible therapeutic delivery technique for treating inner ear disorders while preserving residual cochlear function.

OBJECTIVES:There is currently no method of diagnosing eosinophilic chronic rhinosinusitis with nasal polyps (ECRSwNP) without histologic evidence of tissue eosinophilia. We aimed to quantify eosinophils in fresh sinonasal tissue using optical coherence tomography (OCT), a non-contact imaging modality, and compare these counts with eosinophils per high-power field (HPF) on histology. METHODS:Sinonasal tissue was collected from patients undergoing endoscopic sinus surgery for CRS. Half of each sample was sent for histologic processing, and eosinophils per HPF were quantified and averaged over three hematoxylin-and-eosin slides per sample. The other half of each tissue sample was imaged with high-resolution OCT directly without histologic processing, and globules with the appearance of eosinophils were counted and averaged over three images per sample. Mean globule counts in OCT images and eosinophils per HPF on histology were correlated. RESULTS:Sinonasal tissue was collected from 14 patients including six with ECRSwNP (42.9%). Mean globules resembling eosinophils in tissue from patients with ECRSwNP were significantly greater than in other patients (101.9 ± 39.9 vs. 24.3 ± 17.1, p < 0.001). There was a statistically significant correlation between globule counts on OCT and eosinophils per HPF on histology across all samples (ρ = 0.90, p < 0.001). A cutoff of 45 globules on OCT was 100% sensitive and 87.5% specific for diagnosing ECRSwNP using a cutoff of 55 eosinophils per HPF on histology. CONCLUSION:OCT may be used to diagnose ECRSwNP in excised sinonasal tissue. These results may serve as a proof-of-concept for developing an intranasal OCT system to diagnose ECRSwNP non-invasively. LEVEL OF EVIDENCE: 4:

We have been investigating Optical Coherence Tomography (OCT) as a tool to measure the tympanic membrane and middle ear morphology and vibrational response. The hand-held OCT ostoscope system, based on a 1.3 µm swept laser, is integrated into an endoscopy cart. It has an ~ 8 mm diameter field of view, 38 µm lateral resolution, 35 µm axial resolution, A-line rate of 200 kHz, and subnanometer sensitivity to vibration within the tympanic membrane and middle ear. The system has been used in the clinic at USC Keck Medical Center to image over 100 patients and healthy volunteers. Total imaging time is ~2 minutes, which allows it to easily fit into the clinic workflow, while providing high-resolution images and vibrometric assessment of the tympanic membrane and middle ear. The functional and morphological features visible within these image sets that allow us to readily differentiate among pathologies, will be discussed.

Significance:Pathologies within the tympanic membrane (TM) and middle ear (ME) can lead to hearing loss. Imaging tools available in the hearing clinic for diagnosis and management are limited to visual inspection using the classic otoscope. The otoscopic view is limited to the surface of the TM, especially in diseased ears where the TM is opaque. An integrated optical coherence tomography (OCT) otoscope can provide images of the interior of the TM and ME space as well as an otoscope image. This enables the clinicians to correlate the standard otoscopic view with OCT and then use the new information to improve the diagnostic accuracy and management. Aim:We aim to develop an OCT otoscope that can easily be used in the hearing clinic and demonstrate the system in the hearing clinic, identifying relevant image features of various pathologies not apparent in the standard otoscopic view. Approach:We developed a portable OCT otoscope device featuring an improved field of view and form-factor that can be operated solely by the clinician using an integrated foot pedal to control image acquisition. The device was used to image patients at a hearing clinic. Results:The field of view of the imaging system was improved to a 7.4 mm diameter, with lateral and axial resolutions of 38    μ m and 33.4    μ m , respectively. We developed algorithms to resample the images in Cartesian coordinates after collection in spherical polar coordinates and correct the image aberration. We imaged over 100 patients in the hearing clinic at USC Keck Hospital. Here, we identify some of the pathological features evident in the OCT images and highlight cases in which the OCT image provided clinically relevant information that was not available from traditional otoscopic imaging. Conclusions:The developed OCT otoscope can readily fit into the hearing clinic workflow and provide new relevant information for diagnosing and managing TM and ME disease.

We present a flexible catheter endoscope using a 3D printed miniature side-viewing reflective lens for OCT imaging. A reflective lens with a depth of field (DOF) of 3mm and a maximum spot size of 80 microns was first designed and optimized in OpticStudio (ZEMAX). The structure of the lens and the fiber mating part of the optic was then constructed using 2-photon polymerization technique, and a gold reflective coating was added as the final step for the reflective lens. The reflective lens was then glued to cleaved optical fiber, and the assembly was covered by a torque coil to allow rotation of the catheter endoscope. This endoscope was used with a fiber-optic rotary joint and custom-built Mach-Zehnder interferometer to acquire OCT images.

Beginning in 2006, optical coherence tomography (OCT) has been adapted for use as a vibrometer for hearing research. The application of OCT in this field, particularly for studying cochlear mechanics, represents a revolutionary advance over previous technologies. OCT provides detailed evidence of the motions of components within the organ of Corti, extending beyond the first-encountered surface of observation. By imaging through the bony capsule as well as through the round window membrane, OCT has measured vibration at multiple locations along the cochlear spiral, in vivo, under nearly natural conditions. In this document, we present examples of recent research findings to illustrate the applications of OCT in studying cochlear mechanics in both normal and impaired ears.