Transparency of ocular structures affects contrast in the retinal image and has an impact on visual quality. Vitreous constitutes the largest volumetric component of the human eye, thus it contributes to the intraocular scattering. The vitreous can contain subtle opacifications causing an increase in scattering and a reduction in vision. We report three-dimensional enhanced depth imaging of the anterior vitreous with SS-OCT. We show visualization of anterior vitreous opacities (floaters). We also demonstrate the quantification of vitreal opacities with respect to the age of the subjects.
The aim of this study was to develop a comprehensive biomechanical model to predict biomechanical properties of all ocular tissues and to compare the simulations with air-puff swept-source OCT data.
We developed a novel rheological model of the whole eye. The cornea and the crystalline lens were modelled as a combination of spring and dashpot(s) to describe their viscoelastic properties. In addition, a mass element was included to model lenticular wobbling after air pulse. Finally, the eye retraction (depending on the fatty and muscle tissues behind the eye globe) was modeled by a parallel combination of a spring and dashpot elements, and a mass component described the weight of the eye.
We measured deformation profiles of ocular components of the human eyes in-vivo using long-range SS-OCT instrument integrated with air-puff stimulation, which enables to visualize the dynamics of eye through its entire length and to measure the intraocular distances (SS-OCT ocular biometer). The deformations calculated from the model were fitted to the measured profiles data using Levenberg-Marquardt method. The rheological model allowed for predicting the displacements of the cornea and the crystalline lens (1.25mm and 0.115mm, respectively), the eye retraction (0.28mm) and the axial wobbling of the lens within 40ms. The developed model outcomes match well to experimental data of corneal and lenticular hysteresis curves identifying viscoelastic properties of the ocular tissues
In conclusion, the proposed rheological model correctly predicts the effects observed with air-puff SS-OCT ocular biometer and it can be used in future modelling of the whole eye biomechanics.
Transparency of ocular structures is an important factor determining contrast in the retinal image. Although opacities are most commonly formed in the crystalline lens of aging eye (cataract formation), visual function can be also altered by the opacities in the vitreous body. Therefore, macro- and micro-scale visualization of vitreous is clinically relevant since alterations of vitreous organization impact retinal diseases and affect vision. However, optical imaging of the vitreous body is challenging due to its transparency. We demonstrate visualization of vitreous and its opacities in vivo using optical coherence tomography (OCT). We developed a prototype long-depth-range Swept-Source OCT instrument operating at the speed of 30 kA-scans/second and at the central wavelength of 1 μm to perform high-resolution imaging through the entire vitreous depth. The interface with focus-tunable optics has been used to optimize the field of view. 2-D and 3-D OCT data sets of eyes with vitreous opacities were acquired and processed to obtain contrast-enhanced high-resolution images of vitreous. The results demonstrate the ability of the OCT imaging to characterize the opacities that cause floaters. In conclusion, long-depth-range SS-OCT enables volumetric visualization of in vivo microstructural changes in the vitreous body. This instrument might be a useful tool in high-resolution evaluation and surgical management of vitreous opacities.
Optical methods have been recently used to perform objective assessment of crystalline lens and corneal opacities. Swept-source optical coherence tomography (SS-OCT) enables measurements of the back-reflected or back-scattered photons from the internal objects. In this work, we present a long-depth range SS-OCT system, with a focus tunable lens, optimized for the visualization of large sections of the posterior segment of the eye, including the vitreous. The system was validated using an eye model.
Confocal Microscopy (CM) enables 3-D high-resolution images acquisition of biological samples by confocal pinhole application. Whereas transverse scanning can be provided by implementation of scanning mirrors, axial scanning can be achieved by moving the sample, which limits the acquisition speed. On the other hand, with coherence gating Optical Coherence Microscopy (OCM) allows to generate micrometer resolution, cross-sectional images and volumetric data on the internal structure of back-scattering objects. The aim of our study was to assess imaging performance of different designs of CM and OCM with tunable lens technology. Mechanical scanning in axial direction was replaced by remote control of the objective focus position with the two types of lenses: Electrically Tunable Lens (ETL; up to 500 Hz) and Acousto-Optic Lens (AOL; 250 kHz). We compared focus tuning ability of ETL and AOL technologies by applying beam profiling and wavefront sensing. We assessed the impact of tunable lens technology on the CM and OCM system performance. We designed the confocal microscopic system with Bessel beam illumination to extend the depth-of-focus. The axial scanning of the collection point will be provided by our AOL. Combination of Bessel beam illumination and AOL allowed high-speed image acquisition from well-controlled depth positions along with better quality of PSF due to self-healing properties of the Bessel beam. We compared image quality of the proposed configurations with the standard design using biological specimens. To conclude, tunable lens technology implemented to CM and OCM instruments enables enhancement of instrument performance.
Proc. SPIE. 10496, Optical Elastography and Tissue Biomechanics V
KEYWORDS: Eye, Cornea, Coherence (optics), Modulation, Tissues, Optical coherence tomography, Control systems, In vivo imaging, Elastography, Animal model studies
Biomechanical properties of the cornea play key role in accurate measurement of the intraocular pressure (IOP). The aim of this study is to assess the impact of IOP on corneal hysteresis in porcine (ex vivo) and human (in vivo) eyes using swept source optical coherence tomography combined with the air-puff system (air-puff SS-OCT).
We developed air-puff SS-OCT to assess rapid dynamics of porcine corneas during the air pulse application. Both tissue displacement x(t) and air stimulus F(t) are acquired simultaneously that enables generation of corneal hysteresis F(x), which is a direct signature of viscoelastic properties of the cornea. The hysteresis loop can be quantified by calculation the parameters including maximum apex displacement, central corneal thickness, hysteresis area, elastic moduli etc.
Firstly, the corneal response of 35 ex-vivo porcine eyes to the air puff is determined for IOP ranging from 5 to 35 mmHg. The IOP level is set by a custom pressure control system. The IOP causes highly correlated changes in the proposed parameters of the hysteresis curve. Secondly, we investigate the modification of corneal hysteresis in 30 human corneas in vivo. The IOP is modulated by installation of 0,2% brimonidine eye drops (Alphagan) decreasing the IOP. The IOP is measured with air-puff non-contact tonometer (Topcon) and Goldmann tonometer and compared with hystereses generated by air-puff SS-OCT.
To conclude, IOP generates changes of corneal viscoelasticity in ex vivo animal model and in vivo human eyes. Non-invasive character, micrometer resolution and fast acquisition make our approach attractive for in vivo studies.
Transparency of the ocular structures affect the contrast in the retinal image and has an impact on final visual quality. Although opacities are mostly formed in the crystalline lens of aging eye (cataract formation), visual function can be also altered by the opacities in the vitreous body. We demonstrate three-dimensional (3-D) visualization of vitreous opacities in vivo. We developed a prototype long-depth-range Swept-Source OCT instrument operating at the speed of 50 kA-scans/second and at the central wavelength of 1 μm to perform high-resolution imaging of the whole anterior segment of the eye or the retina. Different configurations of the interface with focus-tunable optics have been developed to optimize vitreous imaging. Volumetric data sets of eyes with vitreous opacities were acquired and processed to obtain contrast-enhanced high-resolution images. Vitreous surface segmentation enabled generation of 3-D rendering and en-face views of vitreous opacities in its anterior and posterior interfaces. The results demonstrate the ability of the OCT imaging to characterize the opacities. In conclusion, 3-D long-depth-range SS-OCT enables volumetric visualization of in vivo microstructural changes in the vitreous related to opacification. The instrument might be a useful tool in the high-resolution evaluation and surgical management of vitreous opacities.
In this paper, we use swept source optical coherence tomography combined with air-puff module (air-puff SS-OCT) to
investigate the properties of the cornea. During OCT measurement the cornea was stimulated by short, air pulse, and
corneal response was recorded. In this preliminary study, the air-puff SS-OCT instrument was applied to measure behavior
of the porcine corneas under varied, well-controlled intraocular pressure conditions. Additionally, the biomechanical
response of the corneal tissue before, during and after crosslinking procedure (CXL) was assessed. Air-puff swept source
OCT is a promising tool to extract information about corneal behavior as well as to monitor and assess the effect of CXL.
Availability of the long-depth-range OCT systems enables comprehensive structural imaging of the eye and extraction of biometric parameters characterizing the entire eye. Several approaches have been developed to perform OCT imaging with extended depth ranges. In particular, current SS-OCT technology seems to be suited to visualize both anterior and posterior eye in a single measurement. The aim of this study is to demonstrate integrated anterior segment and retinal SS-OCT imaging using a single instrument, in which the sample arm is equipped with the electrically tunable lens (ETL). ETL is composed of the optical liquid confined in the space by an elastic polymer membrane. The shape of the membrane, electrically controlled by a specific ring, defines the radius of curvature of the lens surface, thus it regulates the power of the lens. ETL can be also equipped with additional offset lens to adjust the tuning range of the optical power. We characterize the operation of the tunable lens using wavefront sensing. We develop the optimized optical set-up with two adaptive operational states of the ETL in order to focus the light either on the retina or on the anterior segment of the eye. We test the performance of the set-up by utilizing whole eye phantom as the object. Finally, we perform human eye in vivo imaging using the SS-OCT instrument with versatile imaging functionality that accounts for the optics of the eye and enables dynamic control of the optical beam focus.
In the last 2 years, the field of micro-electro-mechanical systems tunable vertical cavity surface-emitting lasers (MEMS-VCSELs)
has seen dramatic improvements in laser tuning range and tuning speed, along with expansion into unexplored
wavelength bands, enabling new applications. This paper describes the design and performance of high-speed ultra-broad
tuning range 1050nm and 1310nm MEMS-VCSELs for medical imaging and spectroscopy. Key results include
achievement of the first MEMS-VCSELs at 1050nm and 1310nm, with 100nm tuning demonstrated at 1050nm and
150nm tuning at shown at 1310nm. The latter result represents the widest tuning range of any MEMS-VCSEL at any
wavelength. Wide tuning range has been achieved in conjunction with high-speed wavelength scanning at rates beyond 1
MHz. These advances, coupled with recent demonstrations of very long MEMS-VCSEL dynamic coherence length,
have enabled advancements in both swept source optical coherence tomography (SS-OCT) and gas spectroscopy.
VCSEL-based SS-OCT at 1050nm has enabled human eye imaging from the anterior eye through retinal and choroid
layers using a single instrument for the first time. VCSEL-based SS-OCT at 1310nm has enabled real-time 3-D SS-OCT
imaging of large tissue volumes in endoscopic settings. The long coherence length of the VCSEL has also enabled, for
the first time, meter-scale SS-OCT applicable to industrial metrology. With respect to gas spectroscopy, narrow dynamic
line-width has allowed accurate high-speed measurement of multiple water vapor and HF absorption lines in the 1310nm
wavelength range, useful in gas thermometry of dynamic combustion engines.
Recent advances in swept-source / Fourier domain optical coherence tomography (SS-OCT) technology enable in vivo ultrahigh speed imaging, offering a promising technique for four-dimensional (4-D) imaging of the eye. Using an ultrahigh speed tunable vertical cavity surface emitting laser (VCSEL) light source based SS-OCT prototype system, we performed imaging of human eye dynamics in four different imaging modes: 1) Pupillary reaction to light at 200,000 axial scans per second and 9 μm resolution in tissue. 2) Anterior eye focusing dynamics at 100,000 axial scans per second and 9 μm resolution in tissue. 3) Tear film break up at 50,000 axial scans per second and 19 μm resolution in tissue. 4) Retinal blood flow at 800,000 axial scans per second and 12 μm resolution in tissue. The combination of tunable ultrahigh speeds and long coherence length of the VCSEL along with the outstanding roll-off performance of SS-OCT makes this technology an ideal tool for time-resolved volumetric imaging of the eye. Visualization and quantitative analysis of 4-D OCT data can potentially provide insight to functional and structural changes in the eye during disease progression. Ultrahigh speed imaging using SS-OCT promises to enable novel 4-D visualization of realtime dynamic processes of the human eye. Furthermore, this non-invasive imaging technology is a promising tool for research to characterize and understand a variety of visual functions.
Examination of brain functions in small animal models may help improve the diagnosis and treatment of neurological conditions. Transcranial imaging of small rodents' brains poses a major challenge for optical microscopy. Another challenge is to reduce the measurement time. We describe methods and algorithms for three-dimensional assessment of blood flow in the brains of small animals, through the intact skull, using spectral and time domain optical coherence tomography. By introducing a resonant scanner to the optical setup of the optical coherence tomography (OCT) system, we have developed and applied a high-speed spectral OCT technique that allows us to vary the imaging range of flow and to shorten measurement time. Multi-parameter signal analysis enables us to obtain both qualitative and quantitative information about flow velocity from the same set of data.
We have developed and applied a high-speed Spectral OCT system to image small animal brains. OCT imaging with
high spatial resolution and application of multi-parameter approach enabled cortical blood flow visualization. We
imaged the brain vascular network of an anesthetized mouse stroke model. We demonstrated the impact of induced
stroke on the brain vasculature. The preliminary studies have revealed local ischemia in the areas of the stroke.
In this paper we demonstrate applicability of Optical Coherence Tomography (OCT) for three-dimensional analysis of
blood flow in brain of small animals. We proposed scanning protocols that enable receiving both qualitative and
quantitative information about flow. Presented data are obtained with a laboratory high resolution and high speed
Spectral OCT system. Data analysis is performed using joint Spectral and Time domain OCT.
Recently introduced smart scanning protocols called segmented protocols offer possibility to create Spectral
Optical Coherence Tomography images with strongly reduced speckle contrast. The algorithm is fast, robust and
gives cross-sectional images with preserved high lateral resolution. To obtain efficient speckle reduction only
slight modification to the optical setup is required. Cross-sectional images of anterior and posterior parts of the
human eye with reduced speckle noise are presented.
Proc. SPIE. 7790, Interferometry XV: Techniques and Analysis
KEYWORDS: Signal to noise ratio, Mirrors, Sensors, Blood, Optical coherence tomography, Fourier transforms, In vivo imaging, Tissue optics, Signal detection, Doppler tomography
Recently rapid development of ultrahigh speed optical coherence tomography (OCT) instruments have been observed.
This imaging modality enables performing cross-sectional in vivo imaging of biological samples with speeds of more
than 100,000,000 axial scans per second. This progress has been achieved by the introduction of Fourier domain
detection techniques to OCT instruments. High-speed imaging capabilities lifts the primary limitation of early OCT
technology by giving access to in vivo 3-D volumetric reconstructions in large scales within reasonable time constraints.
New perspectives for existing OCT applications has been added by creating new instrumentation including the functional
imaging. The latter shows a potential to differentiate tissue pathologies via metabolic properties or functional responses.
We present an application of the Joint Spectral and Time domain OCT (STdOCT) method for detection of wide range of
flows in the retinal vessels. We utilized spectral/Fourier domain OCT (SOCT) technique for development of scan
protocols for Doppler signal analysis. We performed retinal imaging in normal eyes using ultrahigh speed (200 000 axial
scans/s) SOCT instrument with a CMOS camera. Various raster scan protocols were implemented for investigation of
blood flow in the retina. Data analysis was performed using the method of joint Spectral and Time domain OCT
(STdOCT). Detection of blood flow velocities ranging from several tens of mm/s to a fraction of mm/s was possible with
scanning methods allowing for appropriate selection of time intervals between data taken for Doppler OCT analysis.
Axial blood flow velocity measurement was possible in retinal vessels. Doppler OCT signal can be utilized as a contrast
mechanism for visualization of retinal capillaries.
We present both axial and transverse components estimation using joint Spectral and Time domain Optical
Coherence Tomography (STdOCT) method. Whereas axial component of velocity vector can be determined
from the time-dependent Doppler beating frequency, the transverse component can be assessed by the analysis of
the broadening of flow velocity profiles (Doppler bandwidth). This enables us to quantitatively determine the
absolute value of the velocity vector. The accurate analyses are performed using well-defined flow of Intralipid
solution in the glass capillary. This enables performing in vivo imaging and allows to calculate velocity maps of
the retinal vasculature.
We present a simple and efficient numerical technique for segmentation retinal and choroidal blood
vasculature with bulk motion correction in functional Doppler Spectral Optical Coherence Tomography
(Doppler SOCT). The technique uses local variance of velocity tomogram which is higher in the areas of
the tomogram with internal flow. The resulting variance map reveals the position of vessels. This can be
used either for vessel segmentation purposes or for masking the vessels on velocity tomograms. The
remaining velocity information is connected only with static structure velocity offset. As only Fourier
transformations are used in calculations the algorithm removes the bulk motion from velocity tomograms
and provides images of segmented vessels with speed of 80 000 lines/s. The algorithm is shown to work
with velocity tomograms obtained by joint Spectral and Time domain OCT (STdOCT).
In this paper we report that optical inhomogeneity of flowing fluid has influence on Doppler OCT measurement.
Additional Doppler signal from scattering steady medium below blood vessels is visible. To investigate this
phenomenon, the experiments with different scattering mediums and different well controlled experimental
configurations were carried out. Imaging was performed using SOCT instrument with CCD camera, and joint Spectral
and Time domain OCT method was used during data analysis.
We show that recently developed joint Spectral and Time Optical Coherence Tomography data analysis
scheme combined with oscillatory change of optical path difference allows for simultaneous complex
ambiguity removal and quantitative flow velocity estimation. Full range structural tomograms as well as
velocity distributions of Intralipid solution in glass capillaries are presented.
We propose a modified method of acquisition and analysis of Spectral Optical Coherence Tomography (SOCT)
data to provide information about flow velocities in three dimensions. Joint Spectral and Time domain Optical
Coherence Tomography (joint STdOCT) enables flow velocity assessment and segmentation of flows. STdOCT
method is based on direct detection of Doppler shift that arises in time during the measurement. New scanning
protocols and analysis tools are proposed to create velocity distribution maps of the retina and to segment and
visualize 3D flows. STdOCT segmentation is more sensitive than methods based on phase measurements and
calculations are more straightforward than other techniques, which require more complex experimental setup and
more sophisticated numerical tools. We also discuss parameters, which improve the flow based segmentation
procedure with special attention paid to the problem of broadening of flow velocity distribution.
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