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Comparative Anatomy and Physiology of the Mammalian Eye
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
The lens is a biconvex transparent structure and is the second refracting unit of the eye. It lies posterior to the iris and is suspended from the ciliary body by the zonular fibers (Figure 21). It also has a posterior attachment to the anterior vitreous face where it lies in a depression of the vitreous, the patellar fossa. It is a unique tissue in that it is avascular, transparent, lacks nerve supply, and has the highest concentration of protein and glutathione in the body.3 Embryologically, the lens originates from the surface ectoderm which is induced to form the lens placode and invaginate by the advancing optic vesicle and cup.167
An overview of human pluripotent stem cell applications for the understanding and treatment of blindness
Published in John Ravenscroft, The Routledge Handbook of Visual Impairment, 2019
Louise A. Rooney, Duncan E. Crombie, Grace E. Lidgerwood, Maciej Daniszewski, Alice Pébay
Many diseases affect multiple cell types and cellular interactions are likely fundamental to normal function and pathogenesis. These are not recapitulated in conventional cell cultures. Recent advances now enable the generation of neural retinas that efficiently replicate the structures that exist in higher organisms (Eiraku et al., 2011; Nakano et al., 2012; Volkner et al., 2016; Zhong et al., 2014). Organised neural retina, or optic cups, can be obtained from the differentiation of hPSCs, giving rise to structures containing stratified layers of retinal cells with RPE, retinal neurons including RGCs, photoreceptors, amacrine cells, horizontal cells and Müller cells (Nakano et al., 2012). By tracing the formation of these organoids in real time, one can gather knowledge on fundamental processes involved in retinogenesis, while simultaneously generating models that more accurately mimic the native eye. Given the inter-relatedness of the cells within the eye, it is important that such models exist, building a more complete picture of developmental processes and disease pathogenesis. Important limitations of the current optic cups are lack of vasculature, microglia and lens placode.
Write short notes on the prenatal development of the lens. Use annotated diagrams where possible
Published in Nathaniel Knox Cartwright, Petros Carvounis, Short Answer Questions for the MRCOphth Part 1, 2018
Nathaniel Knox Cartwright, Petros Carvounis
The optic vesicles appear as outpouchings from the diencephalon (day 25) and grow into close apposition to the surface ectoderm. They induce the ectodermal cuboidal cells to elongate and become columnar, forming the lens placode (day 27).
The Development, Growth, and Regeneration of the Crystalline Lens: A Review
Published in Current Eye Research, 2020
The embryological development of the eye in mammals begins with the formation of the optic pit as a result of the evagination of the ventral forebrain/prechordal mesenchyme (Figure 1).5 The optic pits enlarge to form the optic vesicles and in parallel the overlying surface ectoderm thickens to form the lens placode.58 The lens placode thickens towards the presumptive neural retina of the optic vesicle and both primordial tissues invaginate such that the presumptive neural retina and retinal pigmented epithelium form the optic cup and the folded surface ectoderm forms the lens pit. The lens vesicle forms from the closing of the lens pit and detachment from the surface ectoderm, the lens vesicle matures into the lens and the now closed surface ectoderm differentiates into the cornea.58
Genetics of congenital cataract, its diagnosis and therapeutics
Published in Egyptian Journal of Basic and Applied Sciences, 2018
Luqman Khan, Nargis Shaheen, Qaisar Hanif, Shah Fahad, Muhammad Usman
The lens development is happening through the collections of controlled processes. Embryology and morphogenesis of the eye lens in the animal as well as in human beings provided an insight into the sophisticated and innate disorder that may concern in the characteristic eye phenotypes present in congenital cataract. The optical vesicle that causes the lens is covered by ectodermal cells. The lens placode interferes on the optical vesicle initiate from the forebrain, about the 25 days of pregnancy, it is a shortening of the ectoderm, which is the only layer of cuboidal cells that invaginate into the neural ectoderm of the optic vesicle as the lens depths become clear from the ectoderm by the 33rd day. The anterior epithelial cells at that time they move to the equatorial region and produce the lens bow. The cells in the bow area generate secondary lens fibres in the third gestational month, which spread until they cover the primary lens fibres.
Lack of FOXE3 coding mutation in a case of congenital aphakia
Published in Ophthalmic Genetics, 2018
Yusuke Sano, Yusuke Matsukane, Akihisa Watanabe, Ko-hei Sonoda, Hiroyuki Kondo
The cells of the crystalline lens originate from the surface ectoderm (4,7). The area of the surface ectoderm designated as the lens placode invaginates toward the optic vesicle, so that it becomes the lens pit (4,7). The lens pit separates from the surface ectoderm then close to form the lens vesicle, the primitive crystalline lens (4,7). Congenital primary aphakia is due to the failure in forming the lens placode that can also lead to various other ocular defects including microphthalmia, sclerocornea, absence of iris or ciliary body, dysgenesis of trabecular meshwork, cataracts, Peters’ anomaly, iris coloboma, and optic disc coloboma (1,2).