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Ocular Irritation Testing
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
George P. Daston, F. E. Freeberg
The cornea is composed of five distinct layers. From the outside in these are corneal epithelium, its basement membrane (Bowman’s membrane), a connective tissue stroma, the basement membrane for the corneal endothelium, and the corneal endothelium which borders on the aqueous humor.
Fungal Keratitis Due to Fusarium
Published in Mahendra Rai, Marcelo Luís Occhiutto, Mycotic Keratitis, 2019
Alexandro Bonifaz, Lorena Gordillo-García, Scarlett Fest-Parra, Andrés Tirado-Sánchez, Karla García-Carmona
Trauma to the cornea causes destruction of the epithelium and Bowman’s membrane, which acts as a barrier for infection. The stroma becomes overhydrated and is altered in such a way that it becomes a more favorable site for fungus to grow. Keratomycosis is an occupational hazard of agricultural workers. The seasonal variation observed in other studies may be due to occupational injuries occurred during harvesting (Buitrago-Torrado et al. 2013, Kulkarni et al. 2017, Chidambaram et al. 2018).
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
The cornea is the avascular and transparent outermost layer of the eye, which, in conjunction with the lens, refracts light to the back of the eye. Five layers constitute the human cornea; the corneal epithelium, Bowman’s membrane, the corneal stroma, Descemet’s membrane and the corneal endothelium. The corneal endothelium is largely responsible for the maintenance of corneal transparency as it facilitates transport of necessary solutes and ions to and from other layers of the cornea. Dysfunction of the corneal endothelium can result in corneal blindness, a condition that has predominantly been treated by healthy donor tissue transplantation. However, there is an immense demand for cadaveric human cornea and limited supply, particularly in countries in which eye bank systems are not well established. This necessitates alternative endothelia generation techniques, such as isolation and culture of corneal endothelia cells and generation of corneal cells from hPSCs, for the transplantation and therapy of corneal diseases.
Climatic Droplet Keratopathy Is a Misnomer for This Corneal Degeneration
Published in Seminars in Ophthalmology, 2023
Horacio M. Serra, Pablo A. Moro
CDK is a clinically well-defined entity which can be diagnosed with a careful slit-lamp examination with high magnification even in the early stages. Sometimes a differential diagnosis needs to be made with other corneal degenerations. Its first diagnosis was made with light microscopy and various histochemical stains demonstrating homogenous globular deposits of different sizes, color and forms under the corneal epithelium, within Bowman’s membrane, and in the anterior stroma.4 Klintworth was the first one who used electron microscopic to study the characteristics of the CDK deposits in the cornea of many American patients. Round, electron-dense, featureless material, and sharply demarcated structures not surrounded by basement membrane material and adjacent to disorganized collagen fibrils, were consistently demonstrated in Bowman’s layer and superficial stroma of patients.6 The coalescence and increased volume of these spherules may disrupt Bowman’s membrane, which is associated with the elevation and thinning of the corneal epithelium.35,36
Peters Anomaly: Novel Non-Invasive Alternatives to Penetrating Keratoplasty
Published in Seminars in Ophthalmology, 2023
Raksheeth Nathan Rajagopal, Merle Fernandes
The diagnostic microscopic findings of PA are central excavation of the posterior corneal stroma, Descemet’s membrane, and endothelium with a variable demonstration of iridocorneal and corneo-lenticular adhesion (Figure 1C).8,9,29 Attenuation or absence of Bowman’s membrane has also been noted in some cases, with others reporting thickened or hyperplastic Bowman’s membrane.10,24 Vascularisation and keratinization of the corneal epithelium, myofibroblasts in the corneal stroma, and lesser type I collagen immunoreactivity has been reported in a staphylomatous cornea diagnosed to have PA with secondary ulceration and inflammation.30 Thickened, multi-laminated Descemet’s membrane in the cornea peripheral to the central opacity has also been described in addition to the typical findings in cases of PA.31,32
Eye Make-up Products and Dry Eye Disease: A Mini Review
Published in Current Eye Research, 2022
Mazyar Yazdani, Katja Benedikte Prestø Elgstøen, Tor Paaske Utheim
The corneal epithelium is a barrier to water, chemicals, and microorganisms. It also provides a smooth reflective surface, protects the underlying layers from injury, and contributes to the immune response via its dendritic Langerhans cells. As an outermost layer of the cornea, the epithelium is located above the Bowman’s membrane, stroma, Descemet’s membrane, and endothelium. Its uniform structure comprises a basal layer of cylindric cells, a wing cell layer, and a surface layer of flat cells with ultrastructural microplicae and microvilli. The corneal epithelium is divided into central and peripheral regions. The epithelium of the peripheral cornea has 7–10 cell layers and holds melanocytes or Langerhans cells. In contrast, no such cells exist in the 5–7 layers of the central corneal epithelium.28,29