Aging and myopia are associated with changes in the biomechanical properties of vitreous, inducing fibrous liquefaction. Characterizing vitreous dynamics (rheology) during eye movements can provide a better understanding of biophysical changes in vitreous with disease, as well as provide a quantifiable clinical index of changes from both aging and myopia. Highly sensitive detection of the scattered light intensity in the eye and micrometer image resolution represent advantages of SS-OCT over other technologies to image vitreous. This investigation aims to characterize vitreous dynamics during eye movement. Specifically, we describe a technique for in vivo measurement of vitreous movement tracked over time using high-speed SS-OCT imaging. We also introduce velocimetry analysis of volumetric OCT data sets, enabling the characterization of velocity distributions of vitreous opacities in emmetropic and myopic eyes during horizontal saccades. In vivo imaging was performed with a prototype SS-OCT instrument. We use a manual tracking analysis method to extract velocimetry information on vitreous movement from in vivo data. The velocity of floaters in the vitreous was established by tracking their movement over time, resulting in the hypothesis that the vitreous is more liquid due to the age at which the floaters move faster.
The Oxford nomenclature was developed to distinguish the type of cataract based on the optical signal discontinuity (OSD) zones. The OSD zones were used to distinguish sections within the crystalline lens in our study using OCT images. A swept-source OCT was used to observe in-vivo age-related changes in the crystalline lens from the 50 healthy eyes with the age range of 9 to 78 years. The C3 layer (from oxford nomenclature) of the cortex was identified as the section of the crystalline that contributes highly to the age-related changes. We compared age-related degradation of the optical quality of the crystalline lens measurements using commercial VAO and OQAS systems with a custom-built SS-OCT system.
A high speed motion detection technique using SS-OCT system is demonstrated. Acquired OCT signal from high speed reflector result in producing artifacts like axial position shifts and broadening of the OCT signal in final processed images. A methodology using forward and backward wavelength sweeps of swept source laser to correct these artifacts is proposed. Analysis of phase changes of interferograms recorded with bi-directional laser sweeps at high sweep rates can be used to determine the true trajectory of the fast moving object. This technique also helps in monitoring velocity of the object exceeding the velocity range set by the acquisition speed of the OCT system.
The focusing power of the human eye is provided by the cornea and the crystalline lens (CL). The latter provides the capacity to alter its shape and provide fine focus adjustment during the accommodation process. We extended standard structural OCT analysis to precisely follow dynamically subtle OCT signal phase changes within the human CL during accommodation. Imaging was performed using the SS-OCT system equipped with the Badal system to provide accommodation demand. The presented phase-sensitive analysis allows for distinct motion extraction such as lens wobbling, bulging, or any other deformation that can be significant for crystalline lens accommodation-associated biomechanics.
We demonstrate micro-scale vibrations of the porcine corneas as the result of the stimulation of the eye with air puff. Phase-resolved swept-source optical coherence tomography instrument was used to examine the post-air-puff reaction of the corneas. The impact of the intraocular pressure on vibration amplitude and frequency was examined. The results showed characteristic modes of vibration that will be correlated with the intraocular pressure level. The presented approach represents the next step towards understanding the eye dynamics due to air-puff-based mechanical stimulation.
Confocal Scanning Laser Ophthalmoscope (cSLO) is a retinal imaging technique based on the principle of confocal microscopy which provides high-contrast and high-resolution fundus eye imaging. Acousto-optic lenses (AOL) are tunable lenses enabling fast focus tuning that can be applied in rapid depth scanning. We propose a cSLO integrated with AOL to generate enhanced in vivo retinal images. We present the performance of the optical system based on the tests with eye phantom. The measurements included also determination of the refractive error (spherical defocus).
Swept source OCT was used to image crystalline lens of 100 eyes (age range: 9-78 years) and 3-dimensional lens suture structure was visualized in vivo for the first time. Lens suture patterns were extracted using average intensity projections (AIP) or cortical layers of crystalline lens. Our imaging system has capacity to extract complex star-sutures from cortical layers of lens and simple Y-sutures from fetal nucleus of crystalline lens. Age-related changes in lens and lens sutures were observed and were characterized quantitatively. The developed imaging system can be used to study growth of crystalline lens and its age-related diseases like cataract, presbyopia.
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.
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 this paper we demonstrate applicability of intensity-based optical coherence tomography technique for noninvasive
visualization of 3D retinal microcapillary network. The study was performed with ultra high resolution and high speed
(180,000 Ascans/sec) spectral optical coherence tomography (SOCT). New scanning protocols and data processing
algorithms have been introduced to visualize microcapillary network. Moreover, results obtained in the eyes of healthy
volunteers and patients with eye diseases were compared with fluorescein angiography.
Presented report shows that SOCT is well suited for visualization of 3D retinal capillary network in the healthy and
pathologic eyes as well. Obtained results demonstrate high correspondence with fluorescein angiography, without using
any contrast agents. Our data suggest that intensity-based SOCT has potential in the early diagnosis of the retinal
vascular diseases.
We show results of a project which focuses on detection of activity in neural tissue with Optical Coherence Tomography (OCT) methods. Experiments were performed in neural cords dissected from the American cockroach (Periplaneta americana L.). Functional OCT imaging was performed with ultrahigh resolution spectral / Fourier domain OCT system (axial resolution 2.5 μm). Electrical stimulation (voltage pulses) was applied to the sensory cercal nerve of the neural cord. Optical detection of functional activation of the sample was performed in the connective between the terminal abdominal ganglion and the fifth abdominal ganglion. Functional OCT data were collected over time with the OCT beam illuminating selected single point in the connectives (i.e. OCT M-scans were acquired). Phase changes of the OCT signal were analyzed to visualize occurrence of activation in the neural cord. Electrophysiology recordings (microelectrode method) were also performed as a reference method to demonstrate electrical response of the sample to stimulation.
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 propose two independent OCT data processing methods allowing visualization and analysis of the blood flow.
These methods utilize variations in the OCT intensity images caused by flowing blood. The first method calculates
standard deviation of intensity to generate retinal OCT angiograms. We present algorithm of this method and results of
application for visualization of the microvasculature in the macular area of the human eye in vivo. The second method
calculates cross power spectra of the volumetric intensity images to assess blood flow velocity in three dimensions.
Validation of this method for OCT imaging was performed in a flow phantom.
In this pilot study we demonstrate results of structural Fourier domain OCT imaging of the nervous system of
Periplaneta americana L. (American cockroach). The purpose of this research is to develop an OCT apparatus enabling
structural imaging of insect neural system. Secondary purpose of the presented research is to develop methods of the
sample preparation and handling during the OCT imaging experiments. We have performed imaging in the abdominal
nerve cord excised from the American cockroach. For this purpose we have developed a Fourier domain / spectral OCT
system operating at 820 nm wavelength range.
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.
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