Physiopathology of the Cornea and Physiopathology of Eye Burns

Abstract

The barriers of the eye differ from that of skin in dimensions and mucosal organization: there are epithelial cellular barriers made of lipid layers on the eye and dry surfaces made of proteins in the stratified surfaces of the skin. Skin is protected by a superficial outer fatty film, the stratum corneum, and covered by a thick layer of cells, the basal cellular layer. Thanks to these thick layers, skin has a high resistance to initial diffusion of aqueous fluids and less resistance to lipophilic solvents and to acids. The initial chemical cracking of the lipid layer allows fluids to invade deeper layers of the skin. The basal cell layer and the hair follicles contain stem cells capable of epithelial regeneration.The construction of the eye is completely different. The outer layer of this mucosa consists of a tiny tear layer of lipids and water which covers a superficial epithelium closed by double layer lipid membranes of 30-70 nm size interconnected by tight junctions. Three to seven layers of epithelial cells cover the stromal structures of conjunctiva or cornea. The conjunctival surface has interposed cells secreting small amounts of mucin, the so-called goblet cells, which are typically missing within the corneal epithelium. The regeneration of epithelial structures is due to the limbal stem cells located deep in the Vogt's crypts, for the cornea, and to the conjunctival stem cells lying deep in the fornices, for the conjunctiva.The stroma of cornea and conjunctiva consists of connective tissue, which in the conjunctiva is extremely soft, containing superficial and deep vessels on the sclera located in arterial and venous vessels.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 mm cornea. The corneal stroma consists of highly ordered, horizontally organized and noninterconnected collagen I and X fibrillae that are kept in a hydrated state with a water content of 72-78% and an osmolarity of 420 mOsmol/kg [1].The inner layer of the corneal stroma is a dense membrane of collagen like the basal membrane of the monolayer of corneal endothelium. Descemets membrane is transparent with a thickness varying from 7 to 20 mm, according to the age of the individual. Conjunctiva and cornea host nerve endings of high density in the superficial and basal layers. The cornea at the limbus smoothly changes to sclera with interconnected nontransparent collagen fibrils. Physiological Mechanisms of Decontamination on the EyeIn case of surface contact of fluids with skin, typically nondefatted skin will pearl off the liquids immediately. Defatted skin tends to allow better contact for fluids. The application of soaps or detergents would lessen this initial effect. In contrast to that, the miscibility of

Chemical Properties of Human Amniotic Membrane for Potential Opthalmological Use

“…The concentrations of glucose and protein are about 10 and 30 times lower, respectively, in tear fluid than in serum [45]. The chemical tests run by us on the fresh amniotic membrane specimens revealed a slightly higher Na + , K+ and Cl -, ion concentration (Na + =152 mEq/L; K + =5.74 mEq/ L; Cl -=131.6 mEq/L) than in serum [32], yet comparable to that of ions in the aqueous humor (Na + =152 mEq/L; K + =3.9 mEq/L; Cl -=131.6mEq/L), as reported by Schrage [46].…”

“…We found a total antioxidant capacity (TAC) in hAM of 1.1±0.1 mmol/L (tables 1 and 2), lower than that in serum [46]. However, a team of authors from India reported that tears from healthy people have a total antioxidant capacity (TAC) of 0.7 ± 0.18 mmol/L, with a range of 0.41-1.03mmol/L [42], i.e.…”