Epithelium conjunctiva

In humans, cases of dermatitis have been described after contact with DHBs. Combined exposure to hydroquinone and quinone airborne concentrations causes eye irritation, sensitivity to light, injury of the corneal epithelium, and visual disturbances (126). Cases with an appreciable loss of vision have occurred (127). Long-term exposure causes staining due to irritation or allergy of the conjunctiva and cornea and also opacities. Resorcinol and catechol are also irritants for eyes. 

The cornea is the first structure of the eye to be in contact with incident light. It is composed of five distinct layers lying parallel to its surface the outer epithelium, which is continuous with the epithelial layers of the conjunctiva the epithelial basal lamina the keratocyte-containing stroma, which is a collagen structure arranged so that it is transparent Descemet s membrane and, finally, the endothelium adjacent to the aqueous humour. 

A variety of automatic voltage clamp devices with special modifications have been extensively utilized in electrophysiological studies of /sc in several ocular tissues including the amphibian corneal epithelium [42] and human fetal retinal pigment epithelium [43, 44], as well as non-ocular tissues like the rat tracheal epithelium [45], A strong temperature dependency and inhibitory effect of serosally instilled ouabain on the rabbit conjunctival /sc are characteristic of active ion transport driven by Na+/K+-ATPases in the conjunctiva [6, 7],... 

A solution containing 0.5% phenylethanol and 0.9% sodium chloride caused a sensation of smarting in human test subjects when dropped in the eye. Application of a 1% solution to rabbit eyes caused irritation of the conjunctiva and transient clouding of corneal epithelium. 

Two drops of a 10% solution instilled in rabbit eyes caused immediate pain, and the epithelium turned gray within seconds the conjunctivae were hyperemic with moderate discharge and corneas were opaque at 2 days. Corneal clouding gradually, but not completely, cleared with in 6 weeks. 

Dermal/Ocular Effects. Skin rashes have been infrequently reported in humans after inhalation exposure (Gordon 1944 McGuire 1932). No data were available on effects by oral exposure or dermal contact. Because the effects were sporadic, no firm conclusions can be made regarding the potential effects of carbon tetrachloride on the skin in humans. No reports are available on the effects of carbon tetrachloride on the eyes. In mice, selective localization of bound radioactivity was observed in the conjunctival epithelium after intravenous injection (Brittebo et al. 1990). However, in the absence of carbon tetrachloride-induced lesions in the conjunctiva, the significance of this metabolism and molecular binding is not clear. 

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 jnnctions. Three to seven layers of epithelial cells cover the stromal structures of conjunctiva or cornea. The conjnnctival surface has interposed cells secreting small amonnts of mucin, the so-called goblet cells, which are typically missing within the corneal epithelinm. The regeneration of epithelial structnres is dne to the limbal stem cells located deep in the Vogt s crypts, for the cornea. 

This technique facilitates the scleral cicatrization and prevents the formation of scleral ulcers but it does not enable the covering of the comeal surface with a normal phenotype comeal epithelium [8]. It does not completely avoid the development of a conjunctival fibrosis or of symblepharons. The formation of sym-blepharons, 28% in Kuckelkom series, is most often recorded within the first three months. This situation may require the realization of a new Tenon s plastics or of a transplant of conjunctiva, nose, or mouth mucous membrane. 

The superficial epithelial layer of the conjunctiva is continuous with the corneal epithelium and stretches over the conjunctival sacs toward the epidermis of the lids. The stratified epithelium varies in thickness from two to four layers at the junction with eyelid margin skin, to six to eight layers at the junction with corneal epithelium [15], The substantia propria of the conjunctiva is divided into two layers, a superficial lymphoid layer and a deeper fibrous layer. The deeper fibrous layer consists of thick, collagenous, elastic tissue that is rich with vessels [15]. 

Burgalassi, S., et al. 2000. Effect of xyloglucan (tamarind seed polysaccharide) on conjunctiva cell adhesion to laminin and on corneal epithelium wound healing. Eur J Ophthalmol 10 71. 

In addition to the corneal route, topically applied ocular drugs may be absorbed via a noncorneal absorption route that involves drug transport across the bulbar conjunctiva and underlying sclera into the uveal tract and vitreous humor.65 The intercellular spaces of the conjunctival epithelium are wider than those of the corneal epithelium. As a result, the conjunctiva has higher permeability than the cornea to agents such as mannitol, inulin, and FITC-dextran.86 The penetration of peptides, however, is limited by enzymatic degradation.87 The limit of molecular size for conjunctival penetration is between 20,000 and 40,000 Da. Vitreous can act as an aqueous and unstirred diffusion barrier to drug permeation.64... 

At concentrations greater >40 ppm lacrimauon, reddening of conjunctivae, and increased respiration noted. Mortality at 50 ppm after 24 h with gasping and lung edema. Histologic signs included bronchiolitis, desquamated bronchial epithelium, infiltration by polymorphonuclear cells, edema. 

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