Human cornea layers

CRITICAL ASSESSMENT OF THE METHOD Porcine cornea are similar to human cornea in that both have 5-7 layers of epithelial cells and a Bowman s membrane. Bovine cornea differs in that it has 10 layers of epithelial cells and no Bowman s membrane. Porcine and Bovine comeal cultures both differ in certain aspects from in vivo animal cornea. The latter has the presence of an overlying mucin layer... 

Concerning the effects on comeal sensitivity different results were obtained from experimental studies in rabbits and dogs. From the literature it is known, that studies on comeal anesthesia in rabbits should not be directly extrapolated to the human eye because there may be a lack of correlation. Harris et al. reported on investigations on soaps and surfactants, which induced prolonged and profound comeal anesthesia in rabbits but not in humans. They discussed the absence of Bowman s membrane in the rabbit cornea, differences in comeal innervation, and other unknown factors as possible reason for this marked difference between the rabbit and human cornea. As evident from the presented results such a difference exists also between the rabbit and dog cornea. Other factors possibly responsible for the discrepancies between rabbits and humans concerning comeal sensitivity are more loosely arranged stomal lamellae in rabbits, a lower number of epithelial layers of the cornea of rabbits than in humans, differences in the enzyme pattern of the comeal epithelium, and differences in tear composition and turnover rate as well as in the blinking frequency which is much lower in rabbits compared to humans... 

Recent research has demonstrated that adult human corneal endothelial cells can be grown in culture and transplanted into recipient corneas. Because human endothelial cells retain the capacity to proliferate, growth factors and inhibitors are under study as a potential method for regenerating damaged endothelial cells and increasing cell density to restore endothelial layer function. 

The differences in physiology and sensitivity to tested chemicals between rabbit and human eyes. Indeed, the eyes of rabbits appear to present several anatomical and physiological differences when compared to the human eye such as lower tear production, lower blink reflex, thinner cornea, larger corneal surface area, lack of Bowman s layer, larger conjunctival sac, different tear constituents and the presence of nictitating... 

The human eye is composed of several layers (Figure 11.1). The outermost layer contains the sclera, whose function is to protect the eyeball and the cornea, which... 

The eye is an important site relevant to the glaucoma associated with loss of activity alleles (Sect. 7.3.7, vide infra). In the eye (human), P450 IB 1 mRNA is present at a high level in the iris and ciliary body and at lower levels in the cornea, retinal pigment epithelium, and retina [127, 339]. P450 IBl protein is absent in the trabecular network but present in nonpigmented ciliary epithelium, corneal epithelium and keratocytes, both layers of the iris pigmented epithelium, and retina [127, 339]. 

Figure 10.1 shows schematically the structure of the human eye. In detail the structure of the cornea is given. The cornea separates the aqueous humour from the lachrymal fluid and protects the delicate internal structures of the eye from external influences. The cornea is a clear, avascular tissue to which nutrients and oxygen are supplied by the lachrymal fluid and the aqueous humour. It is composed of five layers a lipophilic multilayered epithelium. Bowman s membrane, a hydrophilic stroma, Descemet s membrane and a lipophilic endothelium. 

The EpiOcular corneal model involves culturing normal, human-derived epidermal keratinocytes to form a stratified, squamous epithelium similar to that found in the cornea. The epidermal cells, which are cultured on specially prepared cell-culture inserts using serum-free medium, differentiate to form a multi-layered structure that closely parallels the corneal epithelium. EpiOcular is mitotically and metabolically active and releases many of the pro-inflammatory agents (cytokines) known to be important in ocular irritation and... 

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