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Low-coherence interferometry
Published in Pablo Artal, Handbook of Visual Optics, 2017
Figure 3.11 shows results from a 3D OCT data set recorded in the right eye of a healthy human volunteer. A 40° × 40° scan field was imaged with a raster scan pattern consisting of 1024(x) × 250(y) A-scans. An SD OCT system operating at 70 kA-scans/s was used (Zotter et al. 2012). Figure 3.11a shows an en face intensity projection image (or pseudo-SLO image), which is generated by adding up intensity values along the A-line (z) direction (Jiao et al. 2005). The image covers the macula, the ONH, and the major arcuate retinal vessels. Figure 3.11b shows a B-scan at the position indicated by the yellow line in Figure 3.11a. This papillomacular scan covers the fovea centralis and the inferior rim of the ONH. In the area of the ONH, the thick hyperreflective retinal nerve fiber layer (RNFL) can be clearly observed, as well as a cross section through a major retinal vessel. The large vessel and some smaller vessels on the nasal side cast shadows on the deeper tissue. Figure 3.11c shows an average of 50 consecutive B-scans recorded at the same position as Figure 3.11b. This averaging improves the signal-to-noise ratio and reduces speckle noise. The retinal layer structure, though already well visible in the single frame image (Figure 3.11b), is especially clear and well discernible in this noise-reduced image. The individual retinal layers are labeled in Figure 3.11c and in the magnified zoom-in Figure 3.11d.
ENTRIES A–Z
Published in Philip Winn, Dictionary of Biological Psychology, 2003
The central region of the RETINA is the area with the highest density of PHOTORECEPTORS. In humans the region exclusively contains CONES and lacks the RODS associated with scotopic vision (vision at low light levels). The region is marked by a yellowish pigment that lends the fovea the alternative name of MACULA LUTEA. The cone-rich region contains a pit or 'fovea' which is about 5 in diameter, with a central region (the fovea centralis or FOVEOLA) subtending 1 approximately, containing the smallest diameter photoreceptors in the eye. Behaviourally, the fovea is the area with the highest visual ACUITY and is the region of the retina that an observer turns towards an object in order to inspect it. In normal vision it is the part of the eye that is used for fixation or foveation (see FIXATION POINT).
Comparative Study of the Primate Retina
Published in Jon H. Kaas, Christine E. Collins, The Primate Visual System, 2003
Stone3 proposed and extensively discussed the idea that, in the mammalian retina, the neurons are distributed along the retinal surface following a two-axis topographical pattern. The horizontal axis is dominated by the visual streak, a specialization devoted to processing information coming from the horizon.351× The vertical axis is dominated by the nasotemporal division, a specialization related to stereopsis.3 The fovea centralis of primates and the area centralis of cats and other mammals are located at the junction of those two axes.3 In different mammals, one of the two axes may become a dominant feature of the retinal topography. In mammals with eyes located laterally in the head, such as the rabbit and the agouti, the visual streak is the most salient retinal feature, and the ganglion cell density peaks in the middle of this structure, at the projection of the optical axis.52,53 There is a less prominent peak of large ganglion cells in the nasotemporal division, in the projection of the visual axis.54 In animals with frontalized eyes, such as primates and felids, the nasotemporal division is more important, and the fovea centralis or area centralis is the most prominent retinal feature, located at the junction of the vertical and horizontal axes.3 The ganglion cell topography has been studied counting cell bodies in prepa-rations usually stained by the method of Nissl. Additional criteria were developed to distinguish ganglion cells from other cell bodies of the ganglion cell layer, such as retrograde labeling of ganglion cells, immunocytochemical staining of displaced amacrine cells and astrocytes, and selective counting of displaced amacrine cells and neuroglia after selective degeneration of ganglion cells. In the majority of recent studies, the ganglion cells have been counted in retinal flat mounts, focusing through the layers of the foveal slope (e.g., Perry and Cowey55), although in some works cell densities have been measured in retinal sections followed by stereological corrections (e.g., Rolls and Cowey56). By using these methods, several species of primates were studied, including catarrhines (Homo,57,58 Papio, 59 Macaca,55-57,60 Cercopithecus61), platyrrhines (Samm,565 Cebus,62 Aotus,63-65 Callithrix66), and prosimians (Galago57,67). For interspecies comparisons to be made, it is necessary to use the retinal magnification factor to express retinal eccentricity in angular distance. This scale conversion allows direct comparison between animals with different eye sizes, such as Cebus and Callithrix, or different optical design, such as Cebus and Aotus:68
Tamoxifen related chorioretinal structural changes
Published in Cutaneous and Ocular Toxicology, 2023
İnci Elif Erbahçeci Timur, Vehbi Açıkgöz, Nagihan Uğurlu, Bülent Yalçın, Mehmet Ali Nahit Şendur, Mutlu Hızal, Halil Kara
The same raster scan passing through the fovea was used to determine total choroidal area (TCA), luminal area (LA), stromal area (SA) and choroidal vascularity index (CVI) at 1500 μm from the fovea centralis temporally and then nasally for image binarisation. The segmentation of images was performed based on the protocols described by Agrawal et al. [21] ImageJ software (Version 1.51; https://imagej.nih.gov/ij/) was utilised for image binarisation. The selected image was converted to 8 bits, and a Niblack autolocal threshold tool was performed to obtain a prominent choroidoscleral junction; the image was then marked using the polygon selection tool, with a 1500 μm line temporally and nasally, which consisted of the centre of fovea and a total length of 3000 μm (Figure 2). The selected polygonal area was TCA and was attached to the region of interest (ROI) manager. The image was then converted to red-blue-green to use the colour threshold tool for selecting dark pixels, and the area of dark pixels was defined as LA, which was the vascular area. SA was calculated by subtracting LA from TCA, and CVI was calculated by dividing TCA by LA.
The Influence of Coronary Heart Disease on Retinal Electrophysiological Examination (Full-field, Pattern and Multifocal Electroretinograms)
Published in Current Eye Research, 2022
Jascha Wendelstein, Barbara Fuchs, Annika Reffken, Matthias Bolz, Carl Erb
Retinal autoregulation is a natural protection against varying perfusion and affects vessel contractions in such a way as to ensure a constant blood flow.18 Coronary artery disease is related to retinal vessel abnormalities, impairment of optic nerve head microcirculation and reduction of choroidal thickness.19–21 Colour perception depends on cones, which are mostly located in the barely vascularized fovea centralis, which in turn is supplied by the underlying choriocapillaris.18 The limited autoregulation of blood flow in the choroid makes it more sensitive than the retinal circulation to arteriosclerotic impacts. In addition to other effects, acquired colour and contrast vision deficiencies can be symptoms of arteriosclerotic vessels. Functional loss of bipolar- and ganglion cells caused by arteriosclerotic retinal vessels can be prevented as long as autoregulation of these vessels is preserved.3 Previous studies in our clinic showed that colour perception deficiencies are observed in patients with vascular diseases.22
Differentiation of Underlying Pathologies of Macular Edema Using Spectral Domain Optical Coherence Tomography (SD-OCT)
Published in Ocular Immunology and Inflammation, 2019
Muriel Dysli, René Rückert, Marion R. Munk
ERM is a well-known complication after retinal surgery or occurs due to inflammatory eye conditions. Therefore, uveitic macular edemas are often accompanied with an ERM. The presence of an ERM, in turn, increases the risk of a ME after cataract surgery38, but not uncommonly, an ERM may also be idiopathic and may be present without any known underlying cause. ERM can cause mechanical traction on the retina resulting in intraretinal cysts and spaces with an accumulation of intraretinal fluid.68 ERMs transmit centripetal traction toward the fovea centralis causing retinal fold formation and mountain-shaped retinal thickening.68 This results in a loss of the foveal depression and contour. The foveal avascular zone visible with FA and OCT decreases in size and may be completely lost. The tractional forces result in radial folds of the inner retina, thickening of the ONL and elevation of the EZ with a small foveal detachment.68