Cobo R, Navarro-Sempere A, Mielgo P, Segovia Y, García M
Department of Biotechnology, Faculty of Science, University of Alicante, Alicante, Spain.
J Morphol. 2024 Dec;285(12):e70015. doi: 10.1002/jmor.70015.
The cornea is the transparent part of the eye's outer sheath and the primary refractive element in the optical system of all vertebrates allowing light to focus on the central part of the retina. Maintenance of its curvature and clarity is therefore essential, providing a smooth optical surface and a protective goggle to ensure a focused image on the retina. However, the corneas of birds have been largely overlooked and the structures and mechanisms controlling corneal shape and hence visual acuity remain unknown. In this work, the cornea of a seabird, that is, the yellow-legged gull, has been investigated using light and electron microscopy. Histological examination reveals that, as in other vertebrates, the cornea consists of five layers: outer epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. The corneal epithelium is a nonkeratinized, stratified squamous epithelium approximately 3-4 cells thick that covers the front of the cornea. The surface of the cornea features two types of microprojections, microridges and microvilli. The acellular Bowman's layer is difficult to define because of its gradual transition into the more regularly arranged stroma, which constitute the bulk of the cornea, a collagen-rich central layer that comprises nearly 90% of the thickness of the cornea. The collagen fibrils are of uniform diameter and, within a given lamella, are all parallel to each other and run the entire breadth of the cornea. The lamellae are oriented at various angles with respect to each other. Between the lamellae, most of the keratocytes were concentrated in the central region of the corneal stroma. Desçemet's membrane is well-developed. The endothelium is a single cell-layer thick of approximately 3 µm in depth. The endothelial cells are polygonal and display irregular and interdigitating borders in basolateral plasma membranes. The results shown different diurnal lifestyle characteristics in the yellow-legged gull cornea.
角膜是眼球外层鞘膜的透明部分，是所有脊椎动物光学系统中的主要屈光元件，可使光线聚焦于视网膜的中央部分。因此，维持其曲率和透明度至关重要，它提供了一个光滑的光学表面和一个保护眼罩，以确保视网膜上形成清晰的图像。然而，鸟类的角膜在很大程度上被忽视了，控制角膜形状进而影响视力的结构和机制仍然未知。在这项研究中，我们使用光学显微镜和电子显微镜对一种海鸟——黄腿鸥的角膜进行了研究。组织学检查显示，与其他脊椎动物一样，角膜由五层组成：外层上皮、鲍曼层、基质、后弹力层和内皮。角膜上皮是一层非角化的复层鳞状上皮，约3 - 4个细胞厚，覆盖角膜前部。角膜表面有两种微突起，即微嵴和微绒毛。无细胞的鲍曼层难以界定，因为它会逐渐过渡到排列更规则的基质，基质构成了角膜的主体，是一个富含胶原蛋白的中央层，占角膜厚度的近90%。胶原纤维直径均匀，在给定的板层内，它们彼此平行且贯穿角膜的整个宽度。板层彼此以不同角度排列。在板层之间，大多数角膜细胞集中在角膜基质的中央区域。后弹力层发育良好。内皮是一层单细胞层，深度约为3 µm。内皮细胞呈多边形，在基底外侧质膜上显示出不规则且相互交错的边界。结果显示了黄腿鸥角膜不同的昼夜生活方式特征。
