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.
The early stages of ocular diseases such as Diabetic Retinopathy are manifested by morphological changes in retinal tissue occurring on cellular level. Therefore, a number of ophthalmic diseases can be diagnosed at an early stage by detecting spatial and temporal variations in the scattering profile of retinal tissue. It was recently demonstrated that, OCT can be used to probe the functional response of retinal photoreceptors to external light stimulation [1]-[3]. fUHROCT measures localized differential changes in the retina reflectivity over time resulting from external light stimulation of the retina. Currently the origins of the observed reflectivity changes are not well understood. However, due to the complex nature of retinal physiology using purely experimental approaches in this case is problematic. For example fUHROCT is sensitive to small changes in the refractive index of biological tissue which as demonstrated previously, can result from a number of processes such as membrane hyperpolarization, osmotic swelling, metabolic changes, etc.
In this paper, we present a computational model of interaction between photoreceptor cells and optical plane wave based on the Finite Integration Technique (FIT).
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.
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.
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