Atlas Of Ocular Optical Coherence Tomography
This book provides a collection of optical coherence tomographic (OCT) images of various diseases of posterior and anterior segments. It covers the details and issues of diagnostic tests based on OCT findings which are crucial for ophthalmologists to understand in their clinical practice. Throughout the chapters all aspects of this non-invasive, popular imaging technique, known for ingenuity and accuracy, is clearly illustrated.
Atlas of Ocular Optical Coherence Tomography
Purpose: To investigate the ability of clock-hour, deviation, and thickness maps of Cirrus high-definition spectral-domain optical coherence tomography (HD-OCT) in detecting retinal nerve fiber layer (RNFL) defects identified in red-free fundus photographs in eyes with early glaucoma (mean deviation >-6.0 dB).
Background/aims: This study aimed to establish a wide-field optical coherence tomography (OCT) deviation map obtained from swept-source OCT (SS-OCT) scans. Moreover, it also aimed to compare the diagnostic ability of this wide-field deviation map with that of the peripapillary and macular deviation maps currently being used for the detection of early glaucoma (EG).
Of the 192 eyes, 10 eyes from 7 patients were excluded either because the OCT images and/or color fundus photographs were of poor quality or because they had a history of ocular surgery other than cataract surgery. A total of 182 highly myopic eyes from 113 patients were analyzed. Each subject underwent a complete ophthalmic examination, including axial length measurement using an IOL master (Carl Zeiss Meditec, Dublin, CA), indirect ophthalmoscopy and slit-lamp biomicroscopy, and optical coherence tomography (RS-3000, Nidek, Tokyo, Japan). Fluorescein angiography was performed if mCNV was suspected.
Purpose : Optical coherence tomography (OCT) is a non-invasive imaging modality used for high resolution (10 μ) imaging of ocular tissue. Retinal cell layers are clearly visible on OCT providing a means for quantitative and topographical analysis. Medical atlases are important tools for detecting abnormal structural and anatomical tissue alterations, relative to a standardized normal. They can also serve as a reference for registration of individual images for deformation-based analysis. The purpose of the current study is to present a method for generating an atlas of the human eye using large field of view 3D OCT image volumes.
Foveal thickness (A) and central foveal thickness (B). In A, foveal thickness is defined as the mean thickness within the central 1000-μm diameter area (the central blue circle on the Early Treatment Diabetic Retinopathy Study map). In B, central foveal thickness is defined as the mean thickness measured at the point of intersection of the 6 radial scans on optical coherence tomography. The mean foveal thickness is approximately 30 μm greater than the mean central foveal thickness.
The optical coherence tomographic (OCT) image (A), the fundus image (B), and the false-color map and numeric printout (C) for the right eye of a healthy patient who did not have well-aligned scans. In C, the central blue area corresponding to the fovea is off center superiorly. The OCT software determined the center (mean SD central foveal thickness) to be 207 18 μm. Misaligned scans may give falsely elevated values. I indicates inferior; N, nasal; S, superior; and T, temporal.
Optical coherence tomography (OCT) is a non-invasive imaging modality of structural retina in vivo. Since its development in 1991, OCT has become essential in diagnosing and assessing most vision-threatening conditions in ophthalmology1. A recent advance in OCT technology led to its counterpart, OCT angiography (OCTA), which measures blood flow in retinal microvasculature by obtaining repeated measurements of phase and intensity at the same scanning position2,3. While OCTA can theoretically be obtained using the same OCT hardware, in practice, OCTA requires both hardware and software modifications to existing OCT machines. OCTA can visualize both superficial and deep capillary plexus of the retinal vasculature without an exogenous dye, unlike fluorescein angiography, enabling better detection of overall retinal flow without potential side effects4. Despite the advantages, the use of OCTA is not as widespread as OCT, due to its cost and limited field of view (FOV) on currently commercially available devices, which decreases the ability to assess microvascular complications of retinal vascular diseases. In addition, OCTA requires multiple acquisitions in the same anatomic location, limiting the ability to acquire interpretable images in eyes with unstable visual fixation and motion artifacts from microsaccades5.
To assess the ability of the pix2pix generative adversarial network (pix2pix GAN) to synthesize clinically useful optical coherence tomography (OCT) color-coded macular thickness maps based on a modest-sized original fluorescein angiography (FA) dataset and the reverse, to be used as a plausible alternative to either imaging technique in patients with diabetic macular edema (DME).
One of the most common causes of visual impairment in diabetic patients is diabetic macular edema (DME) [1]. Fluorescein angiography (FA) depicts retinal blood flow over time, revealing the status of retinal perfusion and the presence of leakage from the retinal vasculature. Therefore, it plays a crucial role in the staging of diabetic retinopathy (DR) and evaluation of the retinal vasculature. However, the physical characteristics of fluorescein, which can leak from diseased blood vessels obscuring the fluorescence of underlying tissue, and the invasiveness of the technique makes it not without risks [2]. A popular non-invasive method for diagnosing DR and tracking its laser, medicinal, and surgical treatment is optical coherence tomography (OCT). OCT is inherently risk-free and independent of the physical characteristics of fluorescein, as it does not use a dye [3]. OCT offers a quantitative evaluation of DME and the location of retinal thickness. Geographically, the macular thickness can be represented as a falsely colored topographic map with green and yellow representing normal and near-normal values and areas with progressively increasing retinal thickness being represented by orange, red, and white in agreement with the color-coded scale [4]. DME and its response to treatment are commonly monitored using automated OCT retinal thickness mapping [5]. Standard OCT, however, only offers structural information, and as a result, does not distinguish blood flow within the retinal vasculature and merely offers spatial features. Zones of leakage can be linked to structural changes in the retina by fusing the physiological data from FA with the structural data from OCT, allowing for a more accurate assessment and monitoring of the response of DME to various treatment regimens. The decision-making process during the follow-up of patients with DME may be hindered by the occasional unavailability of either imaging modality [6].
The proposed virtual fluorescein angiography frames for testing the optical coherence tomography macular thickness map generator. (created by Hazem Abdelmotaal). A Dotted hyperfluorescence simulating the appearance of microaneurysms without leakage. a Image (A) after preprocessing similar to the original dataset. B Dotted hyperfluorescence simulating the appearance of microaneurysms with surrounding focal leakage. b Image (B) after preprocessing similar to the original dataset. C Dotted hyperfluorescence simulating the appearance of microaneurysms with surrounding diffuse leakage. c Image (C) after preprocessing similar to the original dataset
Synthetic optical coherence tomography color-coded macular thickness maps examples with various modes of presentation. A Twin image showing the original unprocessed fluorescein angiography frame (left) concatenated with synthetic optical coherence tomography color-coded macular thickness map (right). The synthesized map was pasted on the corresponding optical coherence tomography fundus image provided by a diagrammatic conventional color bar. B and b Two examples of synthetic optical coherence tomography color-coded macular thickness maps pasted on the corresponding ground-truth fluorescein angiography frames provided by a diagrammatic conventional color bar. C and c Two other examples of synthetic optical coherence tomography color-coded macular thickness maps pasted with transparency on the corresponding ground-truth fluorescein angiography frames provided with a diagrammatic conventional color bar
Box-plot of peak signal-to-noise ratio, structural similarity index, Hamming distance and learned perceptual image patch similarity metric between the generated image sample and an equivalent sample of all available test images. Images were synthesized by best generator performance according to the best Férchet Inception Distance score. The notches in the box plot represent the confidence interval around the median. The mean is marked by a triangle. All synthetic images; FA, synthetic fluorescein angiography images; OCT, synthetic optical coherence tomography color-coded macular thickness maps 041b061a72