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Emerging Biomedical Imaging Optical Coherence Tomography
Published in Lawrence S. Chan, William C. Tang, Engineering-Medicine, 2019
Spectral-Domain OCT (SD-OCT): SD-OCT is one of the FD-OCT system methods. The core makeup of SD-OCT is a Michelson-type interferometer and a stationary reference mirror. However, the spectrum of the combined return beams in interference pattern is dispersed and then immediately detected by a high-speed CCD line camera, rather than a point detector. A Fourier transformation is conducted on the spectrally resolved interference pattern and the reflectivity is detected as a function of depth (A-scan) with the upper acquisition speed bound by the read-out rate of the line senor of the camera, usually in the kHz range (Popescu et al. 2011). Typically operated at 800 nm or 1 mm wavelengths with imaging speed at 29,000 to 300,000 lines per second, SD-OCT system has substantially impacted the field of ophthalmology for its ability to generate ultrahigh resolution and 3-dimensional images of in vivo retinal pathology. In addition, SD-OCT provides an important resolution advantage of less than 3 mm, very critical for retinal image even though the speed is acceptably slower, when compared to SS-OCT (Tsai et al. 2014).
ILUMIEN OPTIS Mobile and OPTIS Integrated Technology Overview
Published in Hiram G. Bezerra, Guilherme F. Attizzani, Marco A. Costa, OCT Made Easy, 2017
Fourier-domain OCT (FD-OCT) employs the Fourier-domain detection techniques and results in imaging speeds 10–200 times faster and a detection sensitivity 10- to 100-fold greater than traditional TD-OCT.8–10 While TD-OCT measures the interference signal intensity at different depths, FD-OCT measures the spectrum of the interference signal without the need for mechanically changing the reference path delay. The OCT axial scan can be obtained by applying Fourier transformation on the detected spectrum.8–10 There are two major FD-OCT techniques, including the spectral/Fourier-domain OCT (SD-OCT) and swept-source OCT (SS-OCT). SD-OCT uses a high-speed spectrometer to measure the spectrum of the OCT interference signal and has been broadly used in clinical ophthalmology because it enables ultrahigh resolutions, as well as 3D imaging of retinal pathologies.11–14 SS-OCT uses a wavelength-swept laser light source and a high-speed photodetector to measure the interference spectrum.15–19 SS-OCT enables operation at near-infrared wavelengths of 1 and 1.3 μm, which reduces optical scattering and improves imaging depth in the biological tissues, and thus is an ideal imaging technique for most biomedical applications (Figure 11.1).20
Anterior segment OCT
Published in Pablo Artal, Handbook of Visual Optics, 2017
Standard SD-OCT operating at the 830 nm wavelength region is well suited to the imaging of the posterior segment of the eye. Retinal SD-OCT instrument adopted to AS imaging can image only relatively shallow structures and therefore might be oriented on specific components of the AS of the eye such as cornea (Wang et al., 2011). Early studies with high-resolution imaging systems demonstrated applicability of SD-OCT in the imaging of different corneal pathologies (Christopoulos et al., 2007, Kaluzny et al., 2008, 2009, 2010, Wylegala et al., 2009). Figure 4.6a and b presents exemplary cross sections of the human corneas obtained with ultrahigh-resolution laboratory system equipped with a femtosecond laser. Ultrashort pulses represent very broadband spectrum in Fourier domain, which gave axial resolution of 2 μm in tissue. High axial resolution of the OCT images permits distinguishing layer-like microarchitecture of the cornea with epithelium, Bowman membrane, stroma, and endothelium (Figure 4.6a). This feature is especially useful in the pre- and postsurgical assessment of the cornea (Kaluzny et al., 2014). Figure 4.6b shows remodeling of a new epithelial cell layer after epi-Bowman keratectomy, which appears as a hyper-reflective layer covering corneal stroma. High-resolution imaging enables also visualization of pathologic states of the cornea. Figure 4.6c and d demonstrates deposits on the cornea and the dystrophy of corneal endothelium, respectively.
Clinical Update on Metamorphopsia: Epidemiology, Diagnosis and Imaging
Published in Current Eye Research, 2021
Daren Hanumunthadu, Benedicte Lescrauwaet, Myles Jaffe, Srinivas Sadda, Emily Wiecek, Jean Pierre Hubschman, Praveen J. Patel
SD-OCT is used to assess response to treatment particularly after surgery for many conditions including ERM and retinal detachment in order to demonstrate improvement in retinal anatomy.41,42 SD-OCT has revealed photoreceptor ellipsoid zone displacement in ERM, but has particularly been useful in the monitoring of disease and treatment decisions.43 SD-OCT findings could be discussed with patients, so that the possibility of persistent metamorphopsia due to the underlying ellipsoid zone displacement even after vitrectomy and ERM peel surgery is understood. Indeed, patients with ERM associated with pre-operative disruption of the ellipsoid zone appeared to have persistent metamorphopsia despite complete removal of ERM.44 As previously described, alteration in inner nuclear layer thickness is a potential biomarker for the development for metamorphopsia.39 Similarly, in eyes with idiopathic ERM, the inner retinal layer thickness was significantly thicker and the outer retinal layer thickness was significantly thinner compared with normal controls.2
Relationship of Epiretinal Membrane Formation and Macular Edema Development in a Large Cohort of Uveitic Eyes
Published in Ocular Immunology and Inflammation, 2021
Debarshi Mustafi, Brian K. Do, Damien C. Rodger, Narsing A. Rao
A retrospective analysis was performed of patients examined by the uveitis service between 2015 and 2018 at the Roski Eye Institute of the Keck School of Medicine of the University of Southern California. The inclusion criteria for this study were confirmed diagnosis of uni- or bilateral uveitis with previous SD-OCT imaging (Heidelberg Spectralis; Heidelberg Engineering, Heidelberg, Germany). All SD-OCT imaging was done using volume scans and registration between scans. Patients with isolated scleritis or isolated optic neuritis were excluded, as were those with choroidal neovascularization membranes or subretinal fibrosis. Patients with documented diabetic retinopathy and vein occlusion were also excluded. Altogether 269 patients fulfilled the study criteria. The study was approved by the Institutional Review Board at the University of Southern California and was performed in accordance with the Declaration of Helsinki.
An optometrist’s guide to the top candidate inherited retinal diseases for gene therapy
Published in Clinical and Experimental Optometry, 2021
Fleur O’Hare, Thomas L Edwards, Monica L Hu, Doron G Hickey, Alexis C Zhang, Jiang-Hui Wang, Zhengyang Liu, Lauren N Ayton
In addition to inner segment ellipsoid loss, serial SD-OCT imaging of the macula is useful in monitoring central foveal thickness, macular volume and choriocapillaris thickness, which can assist with evaluation of the rate of disease progression in the central retina.98 The retinal nerve fibre layer and inner retinal layers (nuclear and plexiform layers) may appear thicker than normal in early stage disease, a sign of retinal remodelling, then thin as the disease progresses.99 As such, retinal nerve fibre layer scans on OCT can provide useful information on the stage of disease, and also identify a potential issue during diagnosis. Macular pathology such as oedema is best visualised with SD-OCT.36,100 SD-OCT is also highly valuable in isolating other macular differential diagnoses, for example retinoschisis (splitting or separation of the retina between inner and outer neural layers).