Dual-channel air-pulse optical coherence elastography for frequency-response analysis.

Microliter air-pulse optical coherence elastography (OCE) has recently been proposed for the characterization of soft-tissue biomechanics using transient, sub-nanometer to micrometer-scale natural frequency oscillations. However, previous studies have not been able to provide real-time air-pulse monitoring during OCE natural frequency measurement, which could lead to inaccurate measurement results due to the unknown excitation spectrum. To address this issue, we introduce a dual-channel air-pulse OCE method, with one channel stimulating the sample and the other being simultaneously measured with a pressure sensor. This allows for more accurate natural frequency characterization using the frequency response function, as proven by a comprehensive comparison under different conditions with a diverse range of excitation spectra (from broad to narrow, clean to noisy) as well as a diverse set of sample response spectra. We also demonstrate the capability of the frequency-response analysis in distinguishing samples with different stiffness levels: the dominant natural frequencies increased with agar concentrations (181-359 Hz, concentrations: 1-2%, and maximum displacements: 0.12-0.47 µm) and intraocular pressures (IOPs) for the silicone cornea (333-412 Hz, IOP: 5-40 mmHg, and maximum displacements: 0.41-0.52 µm) under a 200 Pa stimulation pressure. These frequencies remained consistent across different air-pulse durations (3 ms to 35 ms). The dual-channel OCE approach that uses transient, low-pressure stimulation and high-resolution imaging holds the potential to advance our understanding of sample frequency responses, especially when investigating delicate tissues such as the human cornea in vivo.

Corneal Surface Wave Propagation Associated with Intraocular Pressures: OCT Elastography Assessment in a Simplified Eye Model.

Assessing corneal biomechanics in vivo has long been a challenge in the field of ophthalmology. Despite recent advances in optical coherence tomography (OCT)-based elastography (OCE) methods, controversy remains regarding the effect of intraocular pressure (IOP) on mechanical wave propagation speed in the cornea. This could be attributed to the complexity of corneal biomechanics and the difficulties associated with conducting in vivo corneal shear-wave OCE measurements. We constructed a simplified artificial eye model with a silicone cornea and controllable IOPs and performed surface wave OCE measurements in radial directions (54-324°) of the silicone cornea at different IOP levels (10-40 mmHg). The results demonstrated increases in wave propagation speeds (mean ± STD) from 6.55 ± 0.09 m/s (10 mmHg) to 9.82 ± 0.19 m/s (40 mmHg), leading to an estimate of Young's modulus, which increased from 145.23 ± 4.43 kPa to 326.44 ± 13.30 kPa. Our implementation of an artificial eye model highlighted that the impact of IOP on Young's modulus (ΔE = 165.59 kPa, IOP: 10-40 mmHg) was more significant than the effect of stretching of the silicone cornea (ΔE = 15.79 kPa, relative elongation: 0.98-6.49%). Our study sheds light on the potential advantages of using an artificial eye model to represent the response of the human cornea during OCE measurement and provides valuable insights into the impact of IOP on wave-based OCE measurement for future in vivo corneal biomechanics studies.

Deep-learning visualization enhancement method for optical coherence tomography angiography in dermatology.

Optical coherence tomography angiography (OCTA) in dermatology usually suffers from low image quality due to the highly scattering property of the skin, the complexity of cutaneous vasculature, and limited acquisition time. Deep-learning methods have achieved great success in many applications. However, the deep learning approach to improve dermatological OCTA images has not been investigated due to the requirement of high-performance OCTA systems and difficulty of obtaining high-quality images as ground truth. This study aims to generate proper datasets and develop a robust deep learning method to enhance the skin OCTA images. A swept-source skin OCTA system was employed to create low-quality and high-quality OCTA images with different scanning protocols. We propose a model named vascular visualization enhancement generative adversarial network and adopt an optimized data augmentation strategy and perceptual content loss function to achieve better image enhancement effect with small amount of training data. We demonstrate the superiority of the proposed method in skin OCTA image enhancement by quantitative and qualitative comparisons.

In vivo corneal elastography: A topical review of challenges and opportunities.

Clinical measurement of corneal biomechanics can aid in the early diagnosis, progression tracking, and treatment evaluation of ocular diseases. Over the past two decades, interdisciplinary collaborations between investigators in optical engineering, analytical biomechanical modeling, and clinical research has expanded our knowledge of corneal biomechanics. These advances have led to innovations in testing methods (ex vivo, and recently, in vivo) across multiple spatial and strain scales. However, in vivo measurement of corneal biomechanics remains a long-standing challenge and is currently an active area of research. Here, we review the existing and emerging approaches for in vivo corneal biomechanics evaluation, which include corneal applanation methods, such as ocular response analyzer (ORA) and corneal visualization Scheimpflug technology (Corvis ST), Brillouin microscopy, and elastography methods, and the emerging field of optical coherence elastography (OCE). We describe the fundamental concepts, analytical methods, and current clinical status for each of these methods. Finally, we discuss open questions for the current state of in vivo biomechanics assessment techniques and requirements for wider use that will further broaden our understanding of corneal biomechanics for the detection and management of ocular diseases, and improve the safety and efficacy of future clinical practice.

Micron-scale hysteresis measurement using dynamic optical coherence elastography.

We present a novel optical coherence elastography (OCE) method to characterize mechanical hysteresis of soft tissues based on transient (milliseconds), low-pressure (<20 Pa) non-contact microliter air-pulse stimulation and micrometer-scale sample displacements. The energy dissipation rate (sample hysteresis) was quantified for soft-tissue phantoms (0.8% to 2.0% agar) and beef shank samples under different loading forces and displacement amplitudes. Sample hysteresis was defined as the loss ratio (hysteresis loop area divided by the total loading energy). The loss ratio was primarily driven by the sample unloading response which decreased as loading energy increased. Samples were distinguishable based on their loss ratio responses as a function loading energy or displacement amplitude. Finite element analysis and mechanical testing methods were used to validate these observations. We further performed the OCE measurements on a beef shank tissue sample to distinguish the muscle and connective tissue components based on the displacement and hysteresis features. This novel, noninvasive OCE approach has the potential to differentiate soft tissues by quantifying their viscoelasticity using micron-scale transient tissue displacement dynamics. Focal tissue hysteresis measurements could provide additional clinically useful metrics for guiding disease diagnosis and tissue treatment responses.

Spatial Assessment of Heterogeneous Tissue Natural Frequency Using Micro-Force Optical Coherence Elastography.

Analysis of corneal tissue natural frequency was recently proposed as a biomarker for corneal biomechanics and has been performed using high-resolution optical coherence tomography (OCT)-based elastography (OCE). However, it remains unknown whether natural frequency analysis can resolve local variations in tissue structure. We measured heterogeneous samples to evaluate the correspondence between natural frequency distributions and regional structural variations. Sub-micrometer sample oscillations were induced point-wise by microliter air pulses (60-85 Pa, 3 ms) and detected correspondingly at each point using a 1,300 nm spectral domain common path OCT system with 0.44 nm phase detection sensitivity. The resulting oscillation frequency features were analyzed via fast Fourier transform and natural frequency was characterized using a single degree of freedom (SDOF) model. Oscillation features at each measurement point showed a complex frequency response with multiple frequency components that corresponded with global structural features; while the variation of frequency magnitude at each location reflected the local sample features. Silicone blocks (255.1 ± 11.0 Hz and 249.0 ± 4.6 Hz) embedded in an agar base (355.6 ± 0.8 Hz and 361.3 ± 5.5 Hz) were clearly distinguishable by natural frequency. In a beef shank sample, central fat and connective tissues had lower natural frequencies (91.7 ± 58.2 Hz) than muscle tissue (left side: 252.6 ± 52.3 Hz; right side: 161.5 ± 35.8 Hz). As a first step, we have shown the possibility of natural frequency OCE methods to characterize global and local features of heterogeneous samples. This method can provide additional information on corneal properties, complementary to current clinical biomechanical assessments, and could become a useful tool for clinical detection of ocular disease and evaluation of medical or surgical treatment outcomes.

High resolution imaging and quantification of the nailfold microvasculature using optical coherence tomography angiography (OCTA) and capillaroscopy: a preliminary study in healthy subjects.

Background: A wide range of diseases, such as systemic sclerosis, can be diagnosed by imaging the nailfold microcirculation, which is conventionally performed using capillaroscopy. This study applied optical coherence tomography angiography (OCTA) as a novel high resolution imaging method for the qualitative and quantitative assessment of the nailfold microvasculature, and compared OCTA imaging with capillaroscopy. Methods: For qualitative assessment, high resolution OCTA imaging was used to achieve images that contained a wide field of view of the nailfold microvasculature through mosaic scanning. OCTA imaging was also used to observe the characteristic changes in the microvasculature under external compression of the upper arm. For quantitative evaluation, the capillary density and the capillary diameter of the nailfold microvasculature were assessed with both OCTA and capillaroscopy by repeated measurements over 2 days in 13 normal subjects. The results were analyzed using the intraclass correlation coefficient (ICC). Results: OCTA imaging showed the typical nailfold microvasculature pattern, part of which was not directly seen with the capillaroscopy. OCTA imaging revealed significant changes in the nailfold microvasculature when a large external pressure was applied via arm compression, but no significant changes were observed using capillaroscopy. The capillary density measured by OCTA and capillaroscopy was 6.8±1.5 and 7.0±1.2 loops/mm, respectively, which was not significantly different (P=0.51). However, the capillary diameter measured by OCTA was significantly larger than that measured using capillaroscopy (19.1±2.5 vs. 13.3±2.3 µm, P<0.001). The capillary diameter measurements using OCTA and capillaroscopy were highly reproducible (ICC =0.926 and 0.973, respectively). While the capillary diameter measured with OCTA was significantly larger, it was rather consistent with the diameter measured using capillaroscopy (ICC =0.705). Conclusions: This study demonstrated that OCTA is a potentially viable and reproducible tool for the imaging and quantification of the capillaries in the nailfold microvasculature. The results of this study provide a solid basis for future applications of OCTA in qualitative and quantitative assessment of nailfold microcirculation in vivo.

Customized eye modeling for optical quality assessment in myopic femto-LASIK surgery.

Refractive surgery is recognized as an effective method for myopia treatment, but it can induce night vision disturbances such as glare. We present an eye modeling method for the optical quality assessment in response to the structural changes in the eyes by femto-LASIK surgery. Customized eye models were built from the measurements of 134 right eyes pre- and post-operatively. Optical performance was evaluated using spot diagrams, point spread functions (PSFs), modulation transfer functions (MTFs), and chromatic aberrations at various fields (0°-30°), different pupil diameters (2-6 mm), and initial myopias (- 1.25 to - 10.5 D). Pupil size and initial myopia are the two major factors that affect visual performance of post-operative eyes. The results of spot diagrams, PSFs, and MTFs indicated that post-operative visual performance deteriorated as the visual field and pupil size increased, and it was significantly influenced by initial myopia. Post-operative chromatic aberrations were also affected by initial myopia. As pupil size increased, the post-operative longitudinal chromatic aberrations tended to decrease slightly, while the transverse chromatic aberrations remained similar. The use of eye modeling for refractive surgery assessment could possibly provide a more personalized surgical approach, could improve the prediction accuracy of refractive surgery outcomes, and promote the invention and development of better surgical methods.

Factors associated with corneal high-order aberrations before and after femtosecond laser-assisted in situ keratomileusis.

BACKGROUND: Corneal high-order aberrations (HOAs) are related to visual quality. However, the factors associated with corneal HOAs before and after femtosecond laser-assisted in situ keratomileusis (FS-LASIK) have not yet been elucidated. The aim of this study is to observe the factors related to corneal HOAs before and after FS-LASIK. METHODS: Prospective observational study was designed to measure corneal HOAs in 149 eyes of 75 patients before and 6 months after FS-LASIK. The relationship between spherical diopter and corneal parameters, including K1 and K2 (horizontal and vertical refractive power of the cornea, respectively), the aspheric characteristics of the cornea (Q), mean radius of the curvature of the cornea (Rm), and central corneal thickness (CCT), with corneal HOAs were analyzed. RESULTS: The spherical diopter was correlated with trefoil at 30° before surgery and with vertical coma, four-order astigmatism at 0°, trefoil at 30°, spherical aberration, and six-order spherical aberration after surgery (P<0.05). CCT was correlated with vertical coma, four-order astigmatism at 0°, trefoil at 30°, and six-order spherical aberration after surgery (P<0.05). K1 was correlated with spherical aberration and six-order astigmatism at 0° before surgery (P<0.05). K2 was correlated with spherical aberration, six-order astigmatism at 45°, astigmatism at 0°, six-order astigmatism at 0° before surgery, and trefoil at 30° after surgery (P<0.05). Q was correlated with spherical aberration, six-order spherical aberration, and six-order astigmatism at 45° (P<0.05). Rm was correlated with six-order astigmatism at 0°, spherical aberration, six-order astigmatism at 45° before surgery, and astigmatism at 0° after surgery (P<0.05). CONCLUSIONS: Corneal parameters and spherical diopter are related to the HOAs of the cornea before and after FS-LASIK.

In vivo human corneal natural frequency quantification using dynamic optical coherence elastography: Repeatability and reproducibility.

Reliable and quantitative assessment of corneal biomechanics is important for the detection and treatment of corneal disease. The present study evaluates the repeatability and reproducibility of a novel optical coherence tomography (OCT)-based elastography (OCE) method for in vivo quantification of corneal natural frequency in 20 normal human eyes. Sub-micron corneal oscillations were induced by repeated low-force (13 Pa) microliter air pulses at the corneal apex and were observed by common-path phase-sensitive OCT imaging adjacent to a measurement region of 1-6.25 mm2. Corneal natural frequencies were quantified using a single degree of freedom model based on the corneal oscillations. Corneal natural frequencies ranged from 234 to 277 Hz (coefficient of variation: 3.2%; n = 286 for a 2.5 × 2.5 mm2 area; time: 28.6 s). The same natural frequencies can be acquired using a smaller sampling size (n = 9 for 1 mm2) and a shorter time (0.9 s). Spatial distribution and local changes in natural frequencies can be distinguished using denser sampling (e.g., 26 × 41 points for 2.5 × 5 mm2). This novel optical method demonstrates highly repeatable and reliable in vivo measurements of human corneal natural frequencies. While further studies are required to fully characterize anatomical and structural dependencies, this method may be complementary to the current OCE methods used to estimate Young's modulus from strain- or shear-wave-based measurements for the quantitative determination of corneal biomechanics.

In Vivo Human Corneal Shear-wave Optical Coherence Elastography.

SIGNIFICANCE: A novel imaging technology, dynamic optical coherence elastography (OCE), was adapted for clinical noninvasive measurements of corneal biomechanics. PURPOSE: Determining corneal biomechanical properties is a long-standing challenge. Elasticity imaging methods have recently been developed and applied for clinical evaluation of soft tissues in cancer detection, atherosclerotic plaque evaluation, surgical guidance, and more. Here, we describe the use of dynamic OCE to characterize mechanical wave propagation in the human cornea in vivo, thus providing a method for clinical determination of corneal biomechanical properties. METHODS: High-resolution phase-sensitive optical coherence tomography imaging was combined with microliter air-pulse tissue stimulation to perform dynamic elasticity measurements in 18 eyes of nine participants. Low-pressure (0.1 mmHg), spatiotemporally discreet (150 µm, 800 µs) tissue stimulation produced submicron-scale tissue deformations that were measured at multiple positions over a 1-mm2 area. Surface wave velocity was measured and used to determine tissue stiffness. Elastic wave propagation velocity was measured and evaluated as a function of IOP and central corneal thickness. RESULTS: Submicron corneal surface displacement amplitude (range, 0.005 to 0.5 µm) responses were measured with high sensitivity (0.24 nm). Corneal elastic wave velocity ranged from 2.4 to 4.2 m/s (mean, 3.5; 95% confidence interval, 3.2 to 3.8 m/s) and was correlated with central corneal thickness (r = 0.64, P < .001) and IOP (r = 0.52, P = .02). CONCLUSIONS: Phase-sensitive optical coherence tomography imaging combined with microliter air-pulse mechanical tissue stimulation has sufficient detection sensitivity to observe submicron elastic wave propagation in corneal tissue. These measurements enable in vivo corneal stiffness determinations that will be further studied for use with disease detection and for monitoring clinical interventions.

Clinical Corneal Optical Coherence Elastography Measurement Precision: Effect of Heartbeat and Respiration.

Purpose: Normal physiological movements (e.g., respiration and heartbeat) induce eye motions during clinical measurements of human corneal biomechanical properties using optical coherence elastography (OCE). We quantified the effects of respiratory and cardiac-induced eye motions on clinical corneal OCE measurement precision and repeatability. Methods: Corneal OCE was performed using low-force, micro-air-pulse tissue stimulation and high-resolution phase-sensitive optical coherence tomography (OCT) imaging. Axial surface displacements of the corneal apex were measured (M-mode) at a 70-kHz sampling rate and three different stimulation pressures (20-60 Pa). Simultaneously, the axial corneal position was tracked with structural OCT imaging, while the heartrate and respiration were monitored over a 90 second period. Results: Respiratory- and cardiac-induced eye motions have distinctly lower frequency (0.1-1 Hz) and much greater amplitude (up to ± 50 µm movements) than air-pulse-induced corneal tissue deformations (∼250 Hz, <1 µm). The corneal displacements induced during OCE measurements in vivo were -0.41 ± 0.06 µm (n = 22 measurements, coefficient of variation [CV]: 14.6%) and -0.44 ± 0.07 µm (n = 50 measurements, CV: 15.9%), respectively, from two human subjects at 40 Pa stimulation pressure. Observed variation in corneal tissue displacements were not associated with tissue stimulation magnitude, or the amplitude of physiologically induced axial eye motion. Conclusions: The microsecond timescale and submicron tissue displacements observed during corneal OCE measurements are separable from normal involuntary physiological movements, such as the oculocardiac pulse and respiratory movements. Translational Relevance: This work advances innovations in biomedical imaging and engineering for clinical diagnostic applications for soft-tissue biomechanical testing.

Characterization of natural frequencies from nanoscale tissue oscillations using dynamic optical coherence elastography.

We demonstrate the use of OCT-based elastography for soft-tissue characterization using natural frequency oscillations. Sub-micrometer to sub-nanometer oscillations were induced in tissue phantoms and human cornea in vivo by perpendicular air-pulse stimulation and observed by common-path OCT imaging (sensitivity: 0.24 nm). Natural frequency and damping ratio were acquired in temporal and frequency domains using a single degree of freedom method. The dominant natural frequency was constant for different stimulation pressures (4-32 Pa) and measured distances (0.3-5.3 mm), and decreased as the sample thickness increased. The dominant natural frequencies of 0.75-2% agar phantoms were 127-774 Hz (mean coefficient of variation [CV]: 0.9%), and correlated with the square root of Young's moduli (16.5-117.8 kPa, mean CV: 5.8%). These preliminary studies show repeatable in vivo corneal natural frequency measurements (259 Hz, CV: 1.9%). This novel OCE approach can distinguish tissues and materials with different mechanical properties using the small-amplitude tissue oscillation features, and is suitable for characterizing delicate tissues in vivo such as the eye.

Theory and design of Schwarzschild scan objective for Optical Coherence Tomography.

Optical coherence elastography (OCE) is one form of multi-channel imaging that combines high-resolution optical coherence tomography (OCT) imaging with mechanical tissue stimulation. This combination of structural and functional imaging can require additional space to integrate imaging capabilities with additional functional elements (e.g., optical, mechanical, or acoustic modulators) either at or near the imaging axis. We address this challenge by designing a novel scan lens based on a modified Schwarzchild objective lens, comprised of a pair of concentric mirrors with potential space to incorporate additional functional elements and minimal compromise to the available scan field. This scan objective design allows perpendicular tissue-excitation and response recording. The optimized scan lens design results in a working distance that is extended to ~140 mm (nearly 2x the focal length), an expanded central space suitable for additional functional elements (>15 mm in diameter) and diffraction-limited lateral resolution (19.33 µm) across a full annular scan field ~ ± 7.5 mm to ± 12.7 mm.

Large-depth-of-field full-field optical angiography.

A large-depth-of-field full-field optical angiography (LD-FFOA) method is developed to expand the depth-of-field (DOF) using a contrast pyramid fusion algorithm (CPFA). The absorption intensity fluctuation modulation effect is utilized to obtain full-field optical angiography (FFOA) images at different focus positions. The CPFA is used to process these FFOA images with different focuses. By selecting high-contrast areas, the CPFA can highlight the characteristics and details of blood vessels to obtain LD-FFOA images. In the optimal case of the proposed method, the DOF for FFOA is more than tripled using 10 differently focused FFOA images. Both the phantom and animal experimental results show that the LD-FFOA resolves FFOA defocusing issues induced by surface and thickness inhomogeneities in biological samples. The proposed method can be potentially applied to practical biological experiments.

Common-path phase-sensitive optical coherence tomography provides enhanced phase stability and detection sensitivity for dynamic elastography.

Phase-sensitive optical coherence elastography (PhS-OCE) is an emerging optical technique to quantify soft-tissue biomechanical properties. We implemented a common-path OCT design to enhance displacement sensitivity and optical phase stability for dynamic elastography imaging. The background phase stability was greater in common-path PhS-OCE (0.24 ± 0.07nm) than conventional PhS-OCE (1.60 ± 0.11µm). The coefficient of variation for surface displacement measurements using conventional PhS-OCE averaged 11% versus 2% for common-path PhS-OCE. Young's modulus estimates showed good precision (95% CIs) for tissue phantoms: 24.96 ± 2.18kPa (1% agar), 49.69 ± 4.87kPa (1.5% agar), and 116.08 ± 12.14kPa (2% agar), respectively. Common-path PhS-OCE effectively reduced the amplitude of background dynamic optical phase instability to a sub-nanometer level, which provided a larger dynamic detection range and higher detection sensitivity for surface displacement measurements than conventional PhS-OCE.

Design of a k-space spectrometer for ultra-broad waveband spectral domain optical coherence tomography.

Nonlinear sampling of the interferograms in wavenumber (k) space degrades the depth-dependent signal sensitivity in conventional spectral domain optical coherence tomography (SD-OCT). Here we report a linear-in-wavenumber (k-space) spectrometer for an ultra-broad bandwidth (760 nm-920 nm) SD-OCT, whereby a combination of a grating and a prism serves as the dispersion group. Quantitative ray tracing is applied to optimize the linearity and minimize the optical path differences for the dispersed wavenumbers. Zemax simulation is used to fit the point spread functions to the rectangular shape of the pixels of the line-scan camera and to improve the pixel sampling rates. An experimental SD-OCT is built to test and compare the performance of the k-space spectrometer with that of a conventional one. Design results demonstrate that this k-space spectrometer can reduce the nonlinearity error in k-space from 14.86% to 0.47% (by approximately 30 times) compared to the conventional spectrometer. The 95% confidence interval for RMS diameters is 5.48 ± 1.76 µm-significantly smaller than both the pixel size (14 µm × 28 µm) and the Airy disc (25.82 µm in diameter, calculated at the wavenumber of 7.548 µm-1). Test results demonstrate that the fall-off curve from the k-space spectrometer exhibits much less decay (maximum as -5.20 dB) than the conventional spectrometer (maximum as -16.84 dB) over the whole imaging depth (2.2 mm).

Design of high-performance adaptive objective lens with large optical depth scanning range for ultrabroad near infrared microscopic imaging.

We report on the theory and design of adaptive objective lens for ultra broadband near infrared light imaging with large dynamic optical depth scanning range by using an embedded tunable lens, which can find wide applications in deep tissue biomedical imaging systems, such as confocal microscope, optical coherence tomography (OCT), two-photon microscopy, etc., both in vivo and ex vivo. This design is based on, but not limited to, a home-made prototype of liquid-filled membrane lens with a clear aperture of 8mm and the thickness of 2.55mm ~3.18mm. It is beneficial to have an adaptive objective lens which allows an extended depth scanning range larger than the focal length zoom range, since this will keep the magnification of the whole system, numerical aperture (NA), field of view (FOV), and resolution more consistent. To achieve this goal, a systematic theory is presented, for the first time to our acknowledgment, by inserting the varifocal lens in between a front and a back solid lens group. The designed objective has a compact size (10mm-diameter and 15mm-length), ultrabroad working bandwidth (760nm - 920nm), a large depth scanning range (7.36mm in air) - 1.533 times of focal length zoom range (4.8mm in air), and a FOV around 1mm × 1mm. Diffraction-limited performance can be achieved within this ultrabroad bandwidth through all the scanning depth (the resolution is 2.22 µm - 2.81 µm, calculated at the wavelength of 800nm with the NA of 0.214 - 0.171). The chromatic focal shift value is within the depth of focus (field). The chromatic difference in distortion is nearly zero and the maximum distortion is less than 0.05%.

High-resolution 1050 nm spectral domain retinal optical coherence tomography at 120 kHz A-scan rate with 6.1 mm imaging depth.

We report a newly developed high speed 1050nm spectral domain optical coherence tomography (SD-OCT) system for imaging posterior segment of human eye. The system is capable of an axial resolution at ~10 µm in air, an imaging depth of 6.1 mm in air, a system sensitivity fall-off at ~6 dB/3mm and an imaging speed of 120,000 A-scans per second. We experimentally demonstrate the system's capability to perform phase-resolved imaging of dynamic blood flow within retina, indicating high phase stability of the SDOCT system. Finally, we show an example that uses this newly developed system to image posterior segment of human eye with a large view of view (10 × 9 mm(2)), providing detailed visualization of microstructural features from anterior retina to posterior choroid. The demonstrated system parameters and imaging performances are comparable to those that a typical 1 µm swept source OCT would deliver for retinal imaging.

Extended imaging depth to 12 mm for 1050-nm spectral domain optical coherence tomography for imaging the whole anterior segment of the human eye at 120-kHz A-scan rate.

ABSTRACT. We demonstrate a 1050-nm spectral domain optical coherence tomography (OCT) system with a 12 mm imaging depth in air, a 120 kHz A-scan rate and a 10 µm axial resolution for anterior-segment imaging of human eye, in which a new prototype InGaAs linescan camera with 2048 active-pixel photodiodes is employed to record OCT spectral interferograms in parallel. Combined with the full-range complex technique, we show that the system delivers comparable imaging performance to that of a swept-source OCT with similar system specifications.