Müller L J, Pels L, Vrensen G F
Department of Morphology, The Netherlands Ophthalmic Research Institute, Amsterdam, The Netherlands.
Invest Ophthalmol Vis Sci. 1995 Dec;36(13):2557-67.
Proper functioning of the endothelium and proper structural organization of the keratocytes and collagen bundles are of ultimate importance for transparency of the cornea. The role of the endothelium has been investigated extensively, whereas the role of the keratocytes is still unclear. Detailed knowledge on the ultrastructural organization of keratocytes and the relationship between keratocytes and collagen bundles is as essential for understanding corneal transparency as is knowledge of endothelial functioning.
Thirty-five corneas (30 postmortem donor corneas and 5 fresh corneas from the operating theater; age range, 28 to 90 years) were used for light microscopy, transmission electron microscopy, and scanning electron microscopy. Serial frontal sections of the central stroma reaching from epithelium to endothelium and cross-sections were studied. At three levels, reconstructions of the mutual arrangement of keratocytes were made using semithin sections.
Keratocytes have the appearance of highly active cells with an abundancy of organelles. Between the dendritic ramifications of these cells, large amounts of amorphous material is observed. One of the most remarkable observations is the presence of an extensive network of fenestrations along the surface of the keratocytes. Another important observation is the circular arrangement of keratocytes gradually turning clockwise like a corkscrew from epithelium to endothelium.
From the current study, the following conclusions can be drawn: Keratocytes are not quiescent but are highly active cells probably involved in turnover of the extracellular matrix; fenestrations may be of functional relevance with respect to facilitation of diffusion and mechanical attachment of the collagen fibers to the keratocytes; the corkscrew organization of keratocytes suggests that they form completely closed sheets of communicating cells throughout the depth of the cornea, creating equal chances for all light rays to pass one or more keratocytes and thus minimizing variation in light scattering over the entire cornea.
内皮细胞的正常功能以及角膜细胞和胶原束的正常结构组织对于角膜的透明度至关重要。内皮细胞的作用已得到广泛研究，而角膜细胞的作用仍不清楚。了解角膜细胞的超微结构组织以及角膜细胞与胶原束之间的关系，对于理解角膜透明度与了解内皮细胞功能同样重要。
使用35只角膜（30只死后供体角膜和5只来自手术室的新鲜角膜；年龄范围为28至90岁）进行光学显微镜、透射电子显微镜和扫描电子显微镜检查。研究了从上皮到内皮的中央基质的连续额状切片和横断面切片。在三个层面上，使用半薄切片对角膜细胞的相互排列进行重建。
角膜细胞呈现出具有丰富细胞器的高活性细胞外观。在这些细胞的树突分支之间，观察到大量无定形物质。最显著的观察结果之一是沿着角膜细胞表面存在广泛的窗孔网络。另一个重要观察结果是角膜细胞呈圆形排列，从上皮到内皮逐渐像螺旋一样顺时针旋转。
从当前研究中可以得出以下结论：角膜细胞并非静止不动，而是高度活跃的细胞，可能参与细胞外基质的更新；窗孔可能在促进扩散以及胶原纤维与角膜细胞的机械附着方面具有功能相关性；角膜细胞的螺旋状排列表明它们在角膜的整个深度形成完全封闭的连通细胞片，为所有光线提供了平等的机会通过一个或多个角膜细胞，从而使整个角膜上的光散射变化最小化。
