Futuristic Approaches in Vitreoretinal Surgery
Pradeep Venkatesh in Handbook of Vitreoretinal Surgery, 2023
Degenerative diseases of the retina, involving the retinal pigment epithelium and photoreceptors, like retinitis pigmentosa, Leber’s congenital amaurosis [LCA], and Stargardt’s disease contribute significantly to the burden of low vision globally. Until a few decades ago, the mechanism of cell death in photoreceptors and retinal pigment epithelium was not known. However, studies on Royal College of Surgeons [RCS] rats have now shown that apoptosis is a predominant method. It has also been found that photoreceptor cell death often occurs secondary to a genetic defect in the neighbouring retinal pigment epithelial cells. It has been demonstrated that in transfected cell cultures and transgenic mouse lines, expression of certain genes can prevent apoptosis. Hence, for gene-mediated disease, advances in gene therapy may play a significant role in preventing, reversing, or retarding the degenerative process. Studies have also tried to precisely determine the nature of cell death in age-related macular degeneration [ARMD].
Comparative Anatomy and Physiology of the Mammalian Eye
David W. Hobson in Dermal and Ocular Toxicology, 2020
The capillary layer of the choroid, the choriocapillaris, is found in the inner portion just below the retinal pigment epithelium (RPE). It is responsible for the nutrition of the RPE and the outer retina and, in some species, for the entire retinal nutrition. The capillaries form a lobular network and are comprised of typical fenestrated endothelial cells surrounded by a basal lamina that surrounds and is shared by pericytes and smooth muscle cells.3,33,115 These lobules are supplied by a central arteriole and are surrounded by a ring of postcapillary venules.33 These vessels are permeable to fluorescein and horseradish peroxidase. Between the choriocapillaris and the RPE is Bruch’s membrane which, when fully developed, is comprised of five layers: (1) the basement membrane of the RPE, (2) an inner collagenous zone, (3) elastic layer, (4) outer collagenous zone, and (5) the basement membrane of the capillary endothelial cells.3,33 In animals with a cellular tapetum the basal lamina of the RPE and the choriocapillaris fuse, obliterating the other three layers in the region overlying the tapetum.3 Venous drainage from the choroid occurs in four quadrants where blood collects in an ampulla and then drains via one of four vortex veins which penetrate the sclera.
Medical retina
Mostafa Khalil, Omar Kouli in The Duke Elder Exam of Ophthalmology, 2019
The retinal pigment epithelium (RPE) is composed of a single layer of cuboidal epithelial cells containing melanosomes and has many functions: Absorbs light and prevents the scattering of light within the eye.Replenishes the molecules needed for phototransduction.Contains a blood-retinal barrier, which provides a selectively permeable membrane to supply nutrients to the photoreceptors and maintain homeostasis. The blood-retinal barrier is maintained by the zonulae occludentes.Phagocytosis of photoreceptor outer segment membranes.Transport and storage of metabolites and vitamins.
Comparison of Peripheral Blood Inflammatory Indices in Patients with Neovascular Age-related Macular Degeneration and Haemorrhagic Polypoidal Choroidal Vasculopathy
Published in Ocular Immunology and Inflammation, 2023
Wei-Wen Hu, Yi-Keng Huang, Xiong-Gao Huang
Our study results showed that there were no statistically significant differences in age; body mass index; or proportions of sex, smoking, hypertension or hyperlipidaemia among nAMD patients, PCV patients and normal controls. These results were consistent with those of Subhi et al.,11which suggests that nAMD and PCV patients have similar epidemiology and risk factors. Both nAMD and PCV are known to occur in the elderly population, mostly in men, which seems to be associated with male lifestyle, such as smoking, more stressful work and different genetic patterns.12 Smoking and hypertension are both risk factors for nAMD and PCV.3,9 This is because some components of cigarettes, such as tar, carbon monoxide and nitric oxide, can induce oxidative stress in the retina, reduce retinal vascular elasticity, increase blood flow resistance and reduce blood flow velocity. Together, these factors lead to impaired blood circulation in the retinal choroid and a diminished ability of the retinal pigment epithelium to transport metabolites.3,5,10 Previous studies have shown that dyslipidemia is associated with the pathogenesis of nAMD and PCV.9 Metabolic deposition of lipids is involved in the formation of drusen in AMD, and drusen is also a manifestation in patients with PCV.13,14 The cholesteryl ester transfer protein and ATP-binding cassette transporter G1 are the main susceptibility genes in the Asian PCV population.15
Sympathetic Ophthalmia - An Overview
Published in Ocular Immunology and Inflammation, 2023
Mamta Agarwal, Aleksandra Radosavljevic, Mudit Tyagi, Francesco Pichi, Aisha A. Al Dhanhani, Aditi Agarwal, Emmett T. Cunningham
In a study by Kaneko et al., it was shown that in SO mitochondrial oxidative stress causes photoreceptor apoptosis without retinal inflammatory cell infiltration due to increased expression of tumor necrosis factor (TNF)-α, TNF-α receptors, and inducible nitric oxide synthase in the photoreceptors, similar to experimental autoimmune uveoretinitis.74 This molecular mechanism initiates the photoreceptor damage in SO, thus explaining the visual loss in the absence of recognizable retinal changes. Dalen-Fuchs nodules, which are seen in 25–35% of cases, are primarily located in the choroid either beneath the RPE or below neuro sensory retina. They are composed of focal collections of epithelioid cells, lymphocytes, histiocytes, and modified retinal pigment epithelial cells (Figure 1).56 Other depigmented lesions seen in the peripheral fundus in chronic VKH and SO were earlier believed to be Dalen-Fuchs nodules, but Inomata and Rao reported in patients with VKH disease, the depigmented atrophic lesions in the sunset glow fundus represent focal disappearance of RPE cells and areas of chorioretinal adhesions.75
Macular and peripapillary vessel density in myopic eyes of young Chinese adults
Published in Clinical and Experimental Optometry, 2020
Dawei Yang, Dan Cao, Liang Zhang, Cheng Yang, Jianqing Lan, Yan Zhang, Jin Zeng
OCT‐A was performed using the AngioVue OCT‐A system (RTVue‐XR Avanti; Optovue, Fremont, CA, USA, version 2017.1.0.151). Repeatability and reproducibility of the system has been proved reliable by previous researchers.2018 Two imaging sections were obtained from each subject, that comprised a 6 × 6-mm region centred on the fovea and a 4.5 × 4.5-mm scan centred in the optic disc. A split‐spectrum amplitude decorrelation angiography software algorithm was used to compute a flow map of each scan. Motion correction technology incorporated in Optovue software was used to compensate for motion artefacts. Images with inadequate scan quality (score of < 6/10) were excluded from the analysis. Retinal layers were segmented between the inner limiting membrane and the retinal pigment epithelium on the basis of the OCT‐A structural image.
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