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Comparative Anatomy and Physiology of the Mammalian Eye
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
The anterior border of the iris is often discussed as possessing an epi- or endothelial cell layer.36 This is incorrect.3,33 The anterior border is formed by fibroblasts and melanocytes.3,33 They form an almost continuous border, but in those regions where they are absent, a crypt will be seen clinically.33 Peripherally, this layer ends abruptly in man with iris processes extending forward to Schwalbe’s line.33 In lower animals this peripheral portion of the iris inserts as the pectinate ligaments in the area where Descemet’s membrane ends. This angle formed by the cornea and the root of the iris is termed the iridocorneal angle and is the entrance to the trabecular meshwork, the site of outflow of the aqueous humor. This region is discussed further in the section on the aqueous humor.
Secondary Open-Angle Glaucomas
Published in Neil T. Choplin, Carlo E. Traverso, Atlas of Glaucoma, 2014
Jonathan Myers, L. Jay Katz, Anand Mantravadi
Released pigment is carried by aqueous flow into the anterior chamber. Pigment may be phagocytosed by corneal endothelial cells, creating a Krukenberg spindle (Figure 10.2). Pigment may also be deposited in circumferential iris furrows and on the posterior lens surface (Figure 10.3). Aqueous flow carries the pigment to the trabecular meshwork, which is typically heavily pigmented for 360° (Figures 10.4 and 10.5). Pigment deposition anterior to Schwalbe’s line is seen in the inferior 180° (Figure 10.6).
Draw a diagram of the anterior chamber drainage angle and write short notes on the anatomy of the structure
Published in Nathaniel Knox Cartwright, Petros Carvounis, Short Answer Questions for the MRCOphth Part 1, 2018
Nathaniel Knox Cartwright, Petros Carvounis
From anterior to posterior, the following structures may be seen on gonioscopy: Schwalbe’s line, the posterior termination of Descemet’s membrane, appears as an opaque line and lies anterior to the commencement of the trabecular meshworkthe corneal wedge coincides with Schwalbe’s line. It can be identified on gonioscopy as the point where the reflections of a narrow slitlamp beam from the internal and external corneal surfaces meetthe trabecular meshwork, which contains Schlemm’s canal and is attached to the scleral spur. In certain pathological conditions the trabeculum becomes hyperpigmentedthe canal of Schlemm can be seen in some eyes without trabecular pigmentation as a slightly darker line deep to the posterior trabeculum. Schlemm’s canal is lined by endothelium and aqueous passes into it in vacuoles formed from the endothelium of the trabecular meshwork. It is not in direct communication with the aqueousthe scleral spur is one of the most consistent angle landmarks between individuals. It is seen as a shiny white band of sclera running between the trabecular meshwork and ciliary body. The longitudinal muscle fibres of the ciliary muscle insert into the scleral spurthe anterior face of the ciliary body is marked by a pigmented band. Its width depends on the position of iris insertioniris processes can be seen in about one-third of eyes. Iris processes are small insertions of the anterior iris surface which insert at the level of the scleral spur. They are less common with increasing agenormal blood vessels run in a radial direction at the base of the angle recess. Pathological blood vessels may run in any direction.
Quantitative Study of Human Scleral Melanocytes and Their Topographical Distribution
Published in Current Eye Research, 2020
Dan-Ning Hu, Shen Yao, Codrin E. Iacob, Jerome Giovinazzo, Richard B. Rosen, Hans E. Grossniklaus, Jodi Sassoon
Each H&E-section and S-100 stained section was examined microscopically at 100x − 400x magnification by a senior masked reviewer using an Olympus BH2 microscope. In the H&E section, the fibroblasts were recognized by the blue-colored oval nuclei and pink-colored cytoplasm and the melanocytes were recognized as cells with pigment granules in the cytoplasm. In S-100 stained sections, the melanocytes were stained red by AEC, whereas fibroblasts remained unstained by AEC. The numbers of these two cell types were counted in a high magnification (400 X) rectangle field (360 μm x 450 μm, 0.16 mm2). The density of cells was expressed as cell number/mm2 (equal to cell number per high magnification area timed 6.25). Melanocytes and fibroblasts were counted in 10 randomly selected fields (x 400) in each of the anterior, equatorial and posterior areas. The anterior areas began 1 mm behind the Schwalbe’s line and extended 4 mm posteriorly. The equatorial areas began 2 mm anterior to the equator and extended 4 mm posteriorly. The posterior area was a circular region extending 4 mm from the margin of the optic disc
Pilot Study of the Effects of Ambient Light Level Variation on Spectral Domain Anterior Segment OCT-Derived Angle Metrics in Caucasians versus Asians
Published in Current Eye Research, 2018
Anna Dastiridou, Kenneth Marion, Moritz Niemeyer, Brian Francis, Srinivas Sadda, Vikas Chopra
Each OCT image was graded in a masked fashion by two trained grading specialists using verified and validated custom ImageJ software (National Institutes of Health image-analysis software – ImageJ 1.44p; developed by Wayne Rasbands, National Institutes of Health, USA). For all acquisitions, the graders computed two parameters: Schwalbe’s line-angle opening distance (SL-AOD) and Schwalbe’s line-trabecular iris space area (SL-TISA) at the inferior angle, using the 6 o’clock position of the 5-line raster scan. The four other raster line scans were used, as needed, to refine the position of Schwalbe’s line on the chosen scan, in case of uncertainty of the exact anatomical location. The SL-AOD was calculated as the distance between the trabecular meshwork and the iris at Schwalbe’s line. The SL-TISA space is defined as the area between the inner corneo-scleral wall and iris surface, measured 500 microns posteriorly from Schwalbe’s line. Acceptable image quality was confirmed by the operator at the time of acquisition with visualization of the full angle and Schwalbe’s line, allowing for grading of all images. Measurements from both independent graders were recorded to determine intergrader agreement and the average from both gradings was calculated for each OCT image and used in the statistical analysis.
Ophthalmic findings in patients with arterial tortuosity syndrome and carriers: A case series
Published in Ophthalmic Genetics, 2018
Joshua S. Hardin, Yuri A. Zarate, Bert Callewaert, Paul H. Phillips, David B. Warner
It is striking that a disease primarily affecting elastin may have manifestations in the cornea, a tissue structure mainly composed of perpendicularly organized collagen fibers and attendant proteoglycans. However, recent work suggests far greater complexity in corneal tissue with over 3250 unique Swiss-prot annotated proteins in the human cornea.23,24 Immunostaining has demonstrated the presence of tangentially arranged collagen and elastin fibers at Schwalbe’s line,25 and it has been proposed that this arrangement is necessary to resist tension and maintain the shape of the prolate cornea.26,27 Elastin seems to have a key functional role in maintaining the proper elasticity of the corneal stroma and decreased expression and activity of lysyl oxidase (LOX), a critical enzyme for collagen and elastin cross-linking, has been shown in keratectasia.28–30 Recent research on Marfan’s syndrome, a related elastinopathy mainly characterized by progressive aortic root dilatation, ectopia lentis, and skeletal overgrowth, has implicated both increased TGFβ bioavailability and low levels of LOX in association with progressive vascular abnormalities due to mutations in genes encoding the elastic fiber protein fibrilllin-1.31 Although unconfirmed in ATS, similar deficiencies may ultimately be connected to the pathophysiologic and genetic basis of this disorder and its associated corneal thinning and ectasia.