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Ocular media
Published in Fiona Rowe, Visual Fields via the Visual Pathway, 2016
The epithelium is a non-keratinised stratified squamous epithelium. Bowman’s layer is an acellular layer consisting of fine interwoven collagen fibrils. The stroma comprises the majority of the cornea and consists of flattened lamellae composed of collagen fibrils with flattened stellate cells between the lamellae. Descemet’s membrane is a modified basement membrane of the endothelium and is composed of basement membrane glycoproteins, laminin and collagen in a lattice arrangement. The endothelium is a single layer of flattened hexagonal-shaped cells. A potential sixth layer, Dua’s layer, has been proposed between the corneal stroma and Descemet layer forming layer four of six (Dua et al. 2013).
The cornea
Published in Mary E. Shaw, Agnes Lee, Ophthalmic Nursing, 2018
The cornea has five layers from the outermost to the innermost (Wilson and Last 2004), and these are illustrated in Figure 9.1. They are as follows: Epithelium – There are five to six layers of epithelial cells, which are continuous with the conjunctival epithelium. The basement membrane is the innermost layer of the epithelium. The epithelium is the only layer of the cornea that regenerates following trauma.Bowman’s membrane – This is a layer of connective tissue, which does not regenerate when damaged.Stroma – This comprises 90% of the cornea, and is composed of parallel connective tissue.Descemet’s membrane – This is a layer of elastic fibres.Endothelium – This comprises a single layer of endothelial cells, which are metabolically active, and their primary function is the control of stromal hydration. The endothelium elongates when damaged.Recent research by Dua et al. (2013) has discovered an additional layer of the cornea which lies between the stroma and Descemet’s layer. This is dubbed as the Dua’s layer and is a skinny but tough structure measuring just 15 microns thick. Its recognition will have considerable impact on posterior corneal surgery and the understanding of corneal biomechanics and posterior corneal pathology such as acute hydrops, Descemetocele and pre-Descemet’s dystrophies.
Vanadium inhalation effects on the corneal ciliary neurotrophic factor (CNTF): study in a murine model
Published in Cutaneous and Ocular Toxicology, 2023
Isis Mendoza-Aldaba, Nelly López-Valdez, María Eugenia Cervantes-Valencia, Teresa Imelda Fortoul
The cornea occupies the sixth anterior part of the ocular globe and is its principal refraction element. It is structured by five layers: (1) The epithelium, (2) Bowman’s layer, (3) stroma, (4) Descemet’s membrane and (5) the endothelium. A new layer has been described recently in the human cornea as pre-Descemet’s layer or Dua’s layer which is rich in Type VI collagen and located in the posterior area of the stroma below the final layer of keratinocytes [2,3]. The anterior corneal epithelium consists of layers of squamous cells interspersed with dendritic cells and sensitive axons [4]. It has a notorious regenerative capacity, which is sustained from the stem cells in the sclerocorneal limbus and has numerous trigeminal free nerve endings. Additionally, it produces and releases neurotrophic factors to support nerve tropism and healing [5]. Bowman’s layer consists of interwoven collagen fibres which function as a barrier against infection dissemination. This layer has no regenerative properties. The stroma comprises 90% of the whole corneal thickness and builds parallel collagen fibres. Descemet’s layer is made up of Type IV collagen which is produced continuously by the endothelial cells. This layer has regenerative properties. The endothelium is a single squamous cell layer attached by desmosomes and occludens junctions that works as a semipermeable membrane, rich in Na+, K+-ATPase pump sites in the lateral membranes [6], and allows metabolic exchange between the cornea and the aqueous humour [7].
Potential role of ocular surface microbiota in keratoconus etiopathogenesis
Published in Expert Review of Ophthalmology, 2021
Uğur Tunç, Yusuf Yıldırım, Ali Rıza Cenk Çelebi, Burçin Kepez Yıldız
The cornea is a transparent avascular tissue that acts as a structural barrier and protects the eye against infections. It is a six-layered structure that is nourished anteriorly by the ocular tear film and posteriorly by the anterior chamber. The layers of the cornea are the epithelium, Bowman’s layer, stroma, Dua’s layer, Descemet’s membrane, and endothelium. Each layer of the cornea has specific and important tasks, thus any defects in these layers can lead to various corneal diseases.
Structural, ultrastructural, and morphometric study of the zebrafish ocular surface: a model for human corneal diseases?
Published in Current Eye Research, 2018
Domenico Puzzolo, Antonina Pisani, Consuelo Malta, Giuseppe Santoro, Alessandro Meduri, Francesco Abbate, Giuseppe Montalbano, Edward Wylegala, Rosa Alba Rana, Fabio Bucchieri, Antonio Ieni, Pasquale Aragona, Antonio Micali
In humans, the cornea is formed by five layers: epithelium, Bowman’s layer, stroma, Descemet’s membrane, and endothelium2,42; recently, a novel acellular layer, the Dua’s layer, placed between posterior stroma and Descemet’s membrane, has been described.43