Cornea tissue

Polypep- tide3 Mol wt (in 1000s) P1 Epidermis (skin) Hair follicle Tissue Cornea Tracheal epithelium He La cellsb Hepatocellular carcinomac... 

FIGURE 4 Influence of emulsion surface charges cyclosporin A (CsA) concentrations in ocular surface tissues (cornea and conjunctiva) following one single-dose (50-pL) instillation of positively (cationic) and negatively (anionic) charged CsA-loaded nanosized emulsions into albino rabbit eye. 

We paid particular attention to the study of physiological and therapeutic effects of silatranes and silocanes on one of the thinnest and most complicated varieties of cormective tissue — cornea. Silatranes effect on cornea was studied after mechanical trauma, and after alkaline and acidic bums. We also studied the effect of silocanes in healing tests with wounds and bums. 

Nevertheless, during recent years, an increasing number of potential commercial applications of femtosecond laser treatment have been demonstrated, e.g., the fabrication of injection nozzles and medical implants (stents) [72]. Some femtosecond laser systems have already been installed particularly for mask repair in industry [73, 74]. In particular, biological tissue (cornea, tooth, bone) can be treated successfully [11, 75, 76]. Even transparent human chromosomes were laser-cut (170 fs, 800 nm, minimum FWHM cut size -100 nm) by a multiphoton-mediated process [77]. But, a killer application is incalculable. 

Cornea is another tissue that is reinforced with collagen fibers. As with cartilage, there is an immediate need for a synthetic substitute to replace damaged corneal tissue. Cornea contains about 20 % of collagen fibers in a gel matrix. The fiber diameter is of the order of 20 nm, so that light is not scattered and the material is transparent [16]. The tensile strength is about 4 MPa and the elastic modulus is about 6 MPa at 20 % strain on the J-shaped stress-strain curve [17]. 

Diclofenac concentrations in cornea (38.1, 108.4, 71.7 and 10.0 /aqueous humor (3.3., 9.4,5.7 and 1.5 ptg/ml) at all time points. Concentrations of diclofenac in both tissues, cornea and aqueous humor, show the same pattern, achieving peak values when contact lenses were applied during 60 minutes. 

The minced tissue, cornea, nucleus pulposus or cartilage, was first treated with proteolytic enzymes, pepsin, tiypsin, or papain. Further removal of the protein, after pepsin treatment, was effected according to Sevag s procedure, or by adsorption on Lloyd s reagent. The polysaccharide mixture vras then fractionated by alcohol precipitation, or by alcohol elution of the barium salt on a cellulose column, or by passage through Dowex-i or Sephadex columns. 

On a vitamin A-deficient diet, mucus-secreting tissues become keratinized. This condition tends to occur in the trachea, the skin, the saUvary glands, the cornea, and the testes. When this occurs in the cornea, it can be followed by blindness. Vitamin A deficiency is the principal cause of blindness in the very young. This problem is particularly acute in the third world (8). 

Vision is vital for human activities, and eyes are very sensitive to a number of toxic insults induced by chemical compounds. The most serious outcome is permanent eye damage which may be so severe as to cause loss of vision. The eye consists of the cornea and conjunctiva, the choroid, the iris, and the ciliary body. It also contains the retina, which is of neural origin, and the optic nerve. The retina contains photoreceptors, a highly specific light-sensitive type of neural tissue. The eye also contains the lens and a small cerebrospinal fluid system, the aqueous humor system, that is important for the maintenance of the steady state of hydration of the lens and thus the transparency of the eye. 

Another widespread application of cold storage of tissue for transplantation is that of preservation of the cornea. Inj uries leading to corneal scarring, various kinds of diseases, and the production of comeal opacity are leading causes of blindness. Cornea transplantation is a commonly used and highly successful procedure. It... 

Taylor, M.J. (1986). Clinical cryobiology of tissues Preservation of corneas. Cryobiology 23,323-353. 

As shown in Figure 48-8, the keratan sulfates consist of repeating Gal-GlcNAc disaccharide units containing sulfate attached to the 6 position of GlcNAc or occasionally of Gal. Type 1 is abundant in cornea, and type II is found along with chondroitin sulfate attached to hyaluronic acid in loose connective tissue. Types I and II have different attachments to protein (Figure 48—8). 

Fibrobiasts, ieukocytes, tissues, amniotic fiuid ceiis, or serum can be used for the assay of many of the above enzymes. Patients with these disorders exhibit a variety of ciinicai findings that may inciude cioudy corneas, mentai retardation, stiff joints, cardiac ab-normaiities, hepatospienomegaiy, and short stature, depending on the specific disease and its severity. 

The conventional concentration of benzalkonium chloride in eyedrops is 0.01%, with a range of 0.004-0.02% [111]. While uptake of benzalkonium chloride itself into ocular tissues is limited [113], even lower concentrations of benzalkonium chloride have been reported to enhance corneal penetration of other compounds including therapeutic agents [93,112,114]. The differential effect of this preservative on the cornea compared to the conjunctiva can be exploited to target a drug for corneal absorption and delivery to the posterior segment of the eye [115]. Its use has been proposed as a means of delivering systemic doses by an ocular route of administration [116]. 

This preservative is comparatively new to ophthalmic preparations and is a polymeric quaternary ammonium germicide. Its advantage over other quaternary ammonium seems to be its inability to penetrate ocular tissues, especially the cornea. It has been used at concentrations of 0.001-0.01% in contact lens solutions as well as dry eye products. At clinically effective levels of preservative, POLYQUAD is approximately 10 times less toxic than benzalkonium chloride [87,137], Various in vitro tests and in vivo evaluations substantiate the safety of this compound [137,141,142], This preservative has been extremely useful for soft contact lens solutions because it has the least propensity to adsorb onto or absorb into these lenses, and it has a practically nonexistent potential for sensitization. Its ad-sorption/absorption with high water and high ionic lenses can be resolved by carefully balancing formulation components [143],... 

The most common means of administering drugs to the eye is by topical administration of agents capable of penetrating the cornea and targeting the appropriate tissue for either physiological or medicinal effect [159,160]. The trilaminar structure of the transparent avascular cornea has been described previously. The... 

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