Anterior stroma

These vessels end in arcade-like structures at the limbus. The corneal stroma is made of three different main layers that differ in density of collagen and type of packing. The Bowman s membrane of the anterior stroma is part of the basal membrane of the corneal epithelium and accounts for 5% of the thickness of the central 500-600 pm cornea. The corneal stroma consists of highly ordered, horizontally organized and noninterconnected coUagen I and X fibriUae that are kept in a hydrated state with a water content of 72-78% and an osmolarity of 420 mOsmol/kg [1]. 

Ill/IIIa) anterior stroma (periphery by stromal haze, with... 

Figure 26-31 Anterior stromal puncture procedure. (A) A 25-gauge needle is used to puncture the anterior stroma. (B) NaFl staining after an anterior stromal puncture procedure. (Courtesy of Pat Caroline.)...

A study of 36 patients with rheumatoid arthritis, 26 of whom received chloroquine therapy, showed hyperreflec-tive abnormal particles in the different layers of the cornea in 19 of the 26 patients eyes studied by confocal microscopy [12 ]. These deposits were found in the superficial epitiielium (14/19), basal epithelium (8/19) and anterior stroma (5/19). The deposits were associated statistically with cumulative dosage. 

FIGURE 38.2 Structure of the cornea. Left Representative histology of a rabbit corneal section. Scale bar is 40 pm. Right Transmission electron microscopy of a rabbit eye, demonstrating the ultrastructure of different corneal layers. Scale bar is 4 pm. Labels ce comeal epithelium b basal epithelial cell bll Bowman s-like layer as anterior stroma k keratocytes ps posterior stroma dm Descemet s membrane endo comeal endothelium. Unpublished data. 

Iris The most anterior portion of the uveal layer, separating the anterior chamber from the posterior. It consists of two layers - the stroma and the pigmented epithelium. Color of the iris depends on the amount of melanin in the stroma on reflection from the pigmented epithelium. [NIH]... 

Corneal epithelium Corneal stroma Corneal endothelium Anterior chamber... 

The edema may be benign, thus enabling a complete examination of all the structures of the anterior chamber iris, pupil, and lens. The edema may be medium when it makes the cornea translucent and then only a faded iris can be observed. It may also be important, and then it creates a porcelain Uke cornea, meaning a white cornea, in which none of the structures of the anterior chamber are visible. This stromal edema must not be taken for an epithelial necrosis due to coagulation, which is sometimes present in some specific types of bums. The epithelium with a necrosis can and must be taken off with a cotton wool stick or a scarificator. This epithelium is easy to separate from the eye, in the form of a whitish squame and then lets the transparent stroma to appear (Fig. 7.10). 

The sclera is the outer white tough part of the eye, which is an important structural element, with the site of insertion of extraocular muscles. It covers 80% of the exterior surface and is white and nontransparent. It borders the transparent cornea at the pars planar. The sclera is divided into three layers episclera, stroma, and lamina fusca. Only a limited number of blood vessels, originating from arteriolar branches of the anterior ciliary vessels, are found and superficial vessels are mainly confined to the loose outer episclera. Scleral permeability approximates that of the corneal stroma and has been shown to be permeable to solutes up to 70 kDa in molecular weight [14]. 

The outer surface of the cornea is covered with a smooth layer of stratified corneal epithelium (Figure 3.4). The lower layer of cells is columnar in shape and rests on a basement membrane that sits on top of a thick limiting structure termed Bowman s membrane derived from the corneal stroma below. The corneal stroma is composed of parallel bundles of collagen fibrils termed lamellae and rows or layers of branching corneal fibroblasts termed keratocytes. The posterior of the cornea is covered with a low cuboidal epithelium with a wide basement membrane (Descemet s membrane) and rests on the posterior portion of the corneal stroma. The corneal epithelium is normally under tension due to the pressure that is present in the anterior chamber just behind the cornea. The intraocular pressure is between 10 and 20 mm of mercury and is enough to cause the cornea to contract about 5% when it is excised from the eye. Therefore this pressure must be transferred between epithelium via cell-cell junctions. 

Sclera The sclera is the outermost firm coat of the eye that serves as a protective barrier for the sensitive inner parts. It is composed of the same type of collagen fibers as the corneal stroma. However, the fibers are arranged in an irregular network rather than a lattice pattern, which makes the tissue appear opaque compared to the transparent cornea. The white sclera constitutes the posterior five-sixths of the globe, whereas the transparent cornea comprises the anterior one-sixth [17],... 

The iris separates the anterior and posterior chambers and consists of the pigmented epithelial cell layer, the iridial sphincter and dilator muscles, and the stroma. The amount of melanin present in the stroma determines the color of the iris few... 

Bowman s layer is the modified anterior border of stroma in humans.This layer is 8 to 14 mm thick and is composed of clear randomly oriented collagen fibrils surrounded by mucoprotein ground substance. Numerous pores in the inner structure allow the passage of terminal branches of comeal nerves from the stroma into epithelium.The surface of Bowman s layer adjoins the stmcturally distinct epithelial... 

If fluid enters the cornea at a rate fester than it is removed by the endothelial cells, edema results. Fluid accumulates in the epitheUiun as well as the stroma and causes the epitheliiun to separate from Bowman s layer. Clinically, these areas of separation between Bowman s layer and the epitheUiun are called bullae, which appear like small bUsters on the front surfece of the cornea. With time and the normal growth of epithelial cells, these bullae are pushed anteriorly in the cornea and erupt at its surfece. 

Moraxella Negative but can appear as gram positive Diplobacillus Central or inferior Oval with a necrotizing edge that may progress deep into the stroma Gray-white dense anterior stromal abscess Hypopyon common, hyphema possible Responds poorly to antibiotics and slow to heal... 

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