Ocular membranes

The significance of the barrier function of membranes has been the topic of considerable research. The blood-brain barrier and the blood-retinal barrier are well understood, and the microscopic structures imparting and controlling barrier properties have been quite thoroughly investigated and the science reviewed [15, 154-155], The structures and functions of ocular membranes specific to transport associated with ophthalmic drug administration also have been topics of extensive research [15, 157-158],... 

The ocular membranes comprise the cornea (not vascularized) and the eonjuetiva (vascularized). The corneal epithelium consists of five or six layers of nonkeratinized squamous cells, and is considered to be the major pathway for ocular drug penetration [57]. 

Sasaki, H., et al. 1997. In-situ ocular absorption of ophthalmic beta-blockers through ocular membranes in albino rabbits. J Pharm Pharmacol 49 140. 

Several imidazole compounds with peripheral a-adrenoceptor stimulant properties, but no corresponding P-effects, are listed in Table 9-3. Unlike with other direct and indirect agonists, there is no significant neuronal uptake mechanism involved. These first four drugs are used mainly as decongestants on nasal mucosa as well as on ocular membranes. A degree of a2 central stimulation likely accounts for some of the sedation encountered... 

Evaporation of the tear film from the precorneal area can cause changes in the concentration of instilled drug solutions, and therefore can affect the rate of drug transport across the ocular membranes. 

Augapfel, m. eyeball, "apple of the eye. bindehaut, /. ocular conjunctiva, -gef ss-haut, /. chorioid membrane, chorioid. haut, /. sclerotic coat, sclera. 

Antagonists of integrin av 33 inhibit the growth of new blood vessels into tumors cultured on the chick chorioallantoic membrane without affecting adjacent blood vessels, and also induce tumor regression [7]. Antagonists of av 33 also inhibit angiogenesis in various ocular models of retinal neovascularization [7]. 

The ocular irritation caused by cosmetic ingredients has been evaluated by the determination of the amount of histamine contained in tears. Contact of surfactants and the eye tissue cause an immediate dose-dependent release of histamine through direct cytotoxic damage of cell membranes. This method has been tested with sodium lauryl sulfate with volunteers [187]. 

These include absorption by adjacent palpebral and bulbar conjunctiva, with concomitant rapid removal from ocular-tissues by peripheral blood flow. For example, the extensive vascularity of the uvea underlies the bulbar conjunctiva, a mucous membrane, and the sclera, a white tissue providing a tough outer covering [177]. Binding of drug to either external sites, like the tear polymers such as mucins or lysozyme, or internal tissues like the sclera can be detrimental to efficacy. 

The Ocusert Pilo-20 and Pilo-40 Ocular Therapeutic System is an elliptical membrane that is soft and flexible and designed to be placed in the inferior cul-de-sac between the sclera and the eyelid and to release pilocarpine continuously at a steady rate for 7 days. The design of the dosage form is described by Alza in terms of an open-looped therapeutic system, having three major components (a) the drug, (b) a... 

A substance may cause changes at the site of hrst contact (skin, eye, mucous membrane in the respiratory and the gastrointestinal tract), irrespective of whether it can become systemicaUy available. These changes are considered local effects. Local effects may occur as a result of a single exposure or repeated exposure. This section deals with local effects caused by a single ocular, dermal, or inhalation exposure. Local effects following repeated exposure are addressed in Section 4.7. 

Headache and irritation of the ocular and upper respiratory membranes may result from prolonged exposure to excessive concentrations of the vapor. ... 

Toxicology. Triethylamine (TEA) causes ocular effects in humans in animals it is a skin and mucous membrane irritant. 

The obtained results confirm earlier findings where vitamin A-deficient rats were used to prove the uptake of retinyl esters into lung, liver, kidney, and plasma after inhalation thereof (Biesalski, 1996). However, long-term topical administration of high vitamin A concentrations is a well-established therapy in atrophic rhinitis, rhinitis sicca, and metaplastic changes in the nasal or ocular epithelium (Deshpande et ah, 1997 Simm, 1980). The application leads to the normalization of mucous membranes and reappearance of a normal function with no side effects. 

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