Cornea mechanism

In recent years considerable attention has focused on the mechanisms of oxidative damage to the cornea. In a study to determine the interaction of ascorbate, hydrogen peroxide and oxygen in the eye, Riley et al. (1986) found that ascorbate promoted corneal swelling when isolated corneas were perfused with glucose-deficient medium. This was due to the rapid oxidation of... 

Bacterial keratitis is a broad term for a bacterial infection of the cornea. This includes corneal ulcers and corneal abscesses. The cornea in a healthy eye has natural resistance to infection, making bacterial keratitis rare. However, many factors predispose a patient to bacterial infection by compromising the defense mechanisms of the eye (Table 60-5).19... 

Figure 3 Putative model for the mechanism by which biogenic amines stimulate CE secretion across the rabbit corneal epithelium. Epn = epinephrine Nep = norepinephrine Tim = Timolol Ser = serotonin Msg = methysergide Dop = dopamine Hal = haloperi-dol (E = (E-adrenoceptor AC = adenylate cyclase. The scheme is consistent with the observation that epithelial responsiveness to serotonin and dopamine can be blocked by their receptor antagonists haloperidol and methysergide, respectively, and by both timolol treatment and sympathectomy. The probable source of serotonin or dopamine is the sympathetic fibers that innervate the cornea. (From Ref. 284.)...

The cornea is the transparent frontal part of the eye that covers the iris, pupil, and anterior chamber and acts as a part of our visualization system by being the gateway for the external images into back of the eye (Figure 12.1). Furthermore, the cornea provides a refractive function and forms a mechanically tough and chemically impermeable barrier between the eye and environment. Additionally, the cornea also is a part of the ocular biodefense system. 

B. S. Anand and A. K. Mitra. Mechanism of corneal permeation of L-valyl ester of acyclovir targeting the oligopeptide transporter on the rabbit cornea. Pharm Res 19 1194-1202 (2002)... 

The experimental simulation of a chemical bum (Figs. 3.84 and 3.85) is stated on a corrosive such as some IM soda in contact for 3 min with the semipermeable membrane representing the cornea. It favorably shows the time gained, thanks to a solution that physically and chemically helps the pH of the aqueous humor to get back to the safe zone. Here, the point is not only to show the mechanical draining effect at the surface of the membrane/comea (which quickly restores the pH to a normal value), but also to show how the internal decontamination of a corrosive is important and difficult. The internal decontamination will deal with the amount of corrosive that might have already penetrated into the anterior chamber of the eye. 

Substances that guarantee the chemical and mechanical stability of the cornea are mostly collagen type I and X that are mainly made of proline and hydroxy-proline. Other substances that are present in a considerable amount are proteins (pK between 5.3 and 9), vitamin C (pK = 4.2), bicarbonate, glutathione, and lactate. (For more details about pK refer to Chap. 3, Sect. 3.2.4.1)... 

A real confirmation that chemical reaction dependent on proteinic pKa is a real mechanism that takes place during the time course of eye bum has been presented by Gerard et al. [4]. They found a time-dependent and stepwise increase of the pH within the cornea after eye bum with ammonia. 

Our body is used to repair small accidents of mechanical or chemical origin. These accidents of biological origin are due to stinging by nettles or insects on eye and skin. Further, there are mechanical damages that are used to be repaired within a short time - as seen in the ex vivo eye irritation test (EVEIT) - such as the healing of mechanical damage ex vivo within a short period of 3 days observed on the isolated rabbit cornea (Fig. 5.11a and b). 

Sometimes severe damage of the cornea can occur [29,30]. The conjunctival damage is mostly low due to the good vascularization and fast repair by means of blood refilling of the protective mechanisms. 

To have insight into these mechanisms, we have performed and published several experiments on diffusion of corrosive, rinsing with different osmolar solutions to check the influence of osmolar conditioning of the cornea [8]. Further, we have tried to evaluate the diffusion of corrosive throughout the cornea [9]. In the latest experiments being published under www.acto.de, we present the effect of fluids of different osmolarities and their action on cells. Unpublished data give insight into... 

Burns, F.R., Paterson, C.A. Chemical injuries Mechanisms of corneal damage and repair. In Beuerman, R.W., Crosson, C.E., Kaufman, H.E. (eds.) Healing Processes in the Cornea. Advances in Applied Biotechnology Series, vol. 1, pp. 45-58. Gulf, Houston (1989)... 

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