The aqueous outflow system (AOS) is responsible for maintaining normal intraocular pressure (IOP) in the eye. Structures of the AOS have an active role in regulating IOP in healthy eyes and these structures become abnormal in the eyes with glaucoma. We describe a newly developed system platform to obtain high-resolution images of the AOS structures. By incorporating spectral domain optical coherence tomography (SD-OCT), the platform allows us to systematically control, image, and quantitate the responses of AOS tissue to pressure with a millisecond resolution of pulsed flow. We use SD-OCT to image radial limbal segments from the surface of the trabecular meshwork (TM) with a spatial resolution of ∼5 μm in ex vivo nonhuman primate eyes. We carefully insert a cannula into Schlemm’s canal (SC) to control both pressures and flow rates. The experimental results demonstrate the capability of the platform to visualize the unprecedented details of AOS tissue components comparable to that delivered by scanning electron microscopy, as well as to delineate the complex pressure-dependent relationships among the TM, structures within the SC, and collector channel ostia. The described technique provides a new means to characterize the anatomic and pressure-dependent relationships of SC structures, particularly the active motion of collagenous elements at collector channel ostia; such relationships have not previously been amenable to study. Experimental findings suggest that continuing improvements in the OCT imaging of the AOS may provide both insights into the glaucoma enigma and improvements in its management.
An ultrahigh resolution spectral domain optical coherence tomography (SD-OCT) system is used to observe for the first time in vivo the early effect of sodium iodate (NaIO 3 ) toxicity on retinal morphology. Retinal degeneration is induced in rats via tail vein injection of NaIO 3 and structural changes in the outer retina are assessed longitudinally at baseline and 1, 2, 3, 6, 8, and 10 h, and 12 post drug administration with OCT, H&E histology, and IgG immunochemistry. Disruption of the structural integrity and changes in the optical reflectivity of the photoreceptor inner (IS) and outer segment (OS) layers are observed as early as 1 h post NaIO 3 injection. A new layer is observed in the OCT tomograms to form between the retinal pigmented epithelium and the photoreceptors OS a few hours post NaIO 3 injection. The dynamics and the low optical reflectivity of this layer, as well as cell swelling and disruption of the blood-retina barrier observed in the histological and immunohistochemistry cross-sections suggest that the layer corresponds to temporary fluid accumulation in the retina. Results from this study demonstrate the effectiveness of OCT technology for monitoring dynamic changes in the retinal morphology and provide better understanding of the early stages of outer retina degeneration induced by NaIO 3 toxicity.
Visually evoked fast intrinsic optical signals (IOSs) were recorded for the first time in vivo from all layers of healthy chicken retina by using a combined functional optical coherence tomography (fOCT) and electroretinography (ERG) system. The fast IOSs were observed to develop within ∼ 5 ms from the on-set of the visual stimulus, whereas slow IOSs were measured up to 1 s later. The visually evoked IOSs and ERG traces were recorded simultaneously, and a clear correlation was observed between them. The ability to measure visually evoked fast IOSs non-invasively and in vivo from individual retinal layers could significantly improve the understanding of the complex communication between different retinal cell types in healthy and diseased retinas.
We have outfitted a 1060nm Spectral Domain Optical Coherence Tomography system with a
prototype, high speed infrared linear array camera and a custom spectrally reshaped
superluminescent diode to achieve 5μm axial resolution at 91,911 A-scans/s image acquisition
rate in-vivo in the human retina. 4dB loss of sensitivity was observed as a result of the reduced
integration time (7μs) of the fast camera as compared to similar commercially available cameras
with 14μs integration time and 47kHz readout rate. Fewer motion artefacts were observed in the
retinal images acquired with the fast camera, while the higher axial resolution along with deeper
penetration allowed for improved visualization of fine morphological details such as retinal and
choroidal capillaries and the deep choroidal structure.
A combined ultrahigh resolution optical coherence tomography (UHROCT) and a electroretinography (ERG) system is presented for simultaneous imaging of the retinal structure and physiological response to light stimulation in the rodent eye. The 1060-nm UHROCT system provides ~3×5 µm (axial×lateral) resolution in the rat retina and time resolution of 22 µs. A custom-designed light stimulator integrated into the UHROCT imaging probe provides light stimuli with user-selected color, duration, and intensity. The performance of the combined system is demonstrated in vivo in healthy rats, and in a rat model of drug-induced outer retinal degeneration. Experimental results show correlation between the observed structural and physiological changes in the healthy and degenerated retina.
A computational model for an "ideal" light source for in-vivo UHROCT imaging of human and animal retina is presented. The model considers parameters such as the wavelength dependent absorption of water, the length of the human or animal eye, the power limitations for the imaging beam as defined in the ANSI standard, etc., to determinethe broadest possible spectral bandwidth that can result in the best axial OCT resolution in the 1060nm wavelength region. A custom light source with a re-shaped spectrum was used to verify experimentally the results from the computational model. 4.3µm axial OCT resolution was achieved experimentally in free space, corresponding to 3µm resolution in retinal tissue. A custom imaging probe was developed and optimized with ZEMAX to result in 5 µm transverse resolution in the rat retina. 2D and 3D OCT tomograms acquired in-vivo from rat retinas show visualization of tiny capillaries imbedded in the inner and outer plexiform layers of the rat retinas.
Hypoxia induced corneal swelling was observed and evaluated in healthy human volunteers by use of high speed, ultrahigh resolution optical coherence tomography (UHROCT). Two dimensional corneal images were acquired at a speed of 47,000 A-scans/s with 3µm x 10µm (axial x lateral) resolution in corneal tissue. The UHROCT tomograms showed clear visualization of all corneal layers, including the Bowman's layer and the Descemet's membrane - Endothelium complex. A segmentation algorithm was developed and used for automatic detection of the boundaries of the different corneal layers and evaluation the individual layer thickness as a function of location. Corneal hypoxia was induced by wear of a soft contact lens (SCL) and an eye patch by 2 healthy volunteers for duration of 3 hours. The thickness of all corneal layers was measured as a function of time, prior to, with and after removal of the SCL. Results from the hypoxia study showed different rates of swelling and de-swelling of the individual corneal layers. About 10% increase in the total cornea thickness was observed, similar to the changes in the stroma, the Bowman's membrane swelled by 20%, while no significant change in the thickness was observed in the Descemet's - Endothelium complex.
A high speed (47,000 A-scan/s), high resoluiton FD-OCT system, operating in the 1060nm wavelength range was used to acquire in-vivo 3D image of healthy and pathological rat retinas. The images were acquired with ~4.3µm axial and ~5µm lateral resolution in the rat eye and 102dB sensitivity at 1.3mW optical power of the imaging beam. The images of the healthy rat retinas show increased penetration into the choroid, clear visualization of all intra-retinal layers and the choroidal blood network, as well as part of the underlying sclera. The high imaging resolution of the OCT system is also sufficient for resolving tiny capillaries imbedded in the inner - and outer plexiform layers of the retina. The high data acquisition rate of the FD-OCT system combined with the high axial resolution is also suitable for probing light induced physiological processes in the retina simultaneously with the morphological imaging.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.