Sevel D, Isaacs R
Division of Ophthalmology, Scripps Clinic and Research Foundation, La Jolla, California.
Trans Am Ophthalmol Soc. 1988;86:178-207.
The corneal epithelium is initially a continuation of the surface ectoderm, but later on in development appears to arise from the superficial cells of the corneal stroma. The corneal epithelium varies in thickness depending on the status of the lids, viz either fused or open. When the lids are fused, the epithelium is only 2 to 3 layers in depth. When the lids are separated, a basement membrane is distinguishable and the epithelium is 4 to 5 layers in depth. Bowman's membrane develops from processes of the superficial mesenchymal cells of the stroma that become thickened and are arranged in the long axis of the corneal surface. The corneal stroma develops from in situ mesenchymal tissue and does not migrate from the limbal mesenchymal tissue. The attenuation of the central cornea, early in development, is due to the impingement of the lens against the developing cornea. The central constriction of the cornea has led previous observers to believe that the stroma migrates from the peripheral limbal area towards the center of the cornea. Descemet's membrane arises from processes of the deep mesenchymal cells of the corneal stroma. These processes thicken and become arranged in the long axis of the posterior surface of the cornea. The membrane is initially cellular, and well-defined septae are noted between the cells. With maturity, Descemet's membrane becomes a homogeneous structure. The endothelium is derived from the mesenchymal cells of the posterior stroma. These cells are initially cuboidal but then become flattened. During the early development of the cornea, the tunica vasculosa lentis may play an important role. It is suggested that the anterior chamber is maintained early on by a transudate from the vessels of the tunica vasculosa lentis. The vessels of the tunica vasculosa lentis are compressed by the vanguard of the optic cup against the equator of the lens. With regression of this vascular system, there is a simultaneous development of aqueous humor. The hydrodynamic force of aqueous production assists corneal molding by a vis a tergo affect. Pari passu with this hydrodynamic force, the corneal stromal fibers increase in length and width. The structures involved in aqueous humor production, viz the ciliary epithelium, and the aqueous humor drainage, viz the filtration angle, trabecular meshwork and aqueous veins, develop contemporaneously as the tunica vasculosa lentis regresses. The limiting and fixed stabilizing site is at the limbus, the site of insertion of the rectus muscles. At these sites a dimpling occurs as the cornea is enlarging.
角膜上皮最初是表面外胚层的延续，但在发育后期似乎起源于角膜基质的表层细胞。角膜上皮的厚度因眼睑状态而异，即眼睑是闭合还是张开。当眼睑闭合时，上皮仅2至3层细胞厚。当眼睑分开时，可以区分出基底膜，上皮为4至5层细胞厚。Bowman膜由基质表层间充质细胞的突起发育而来，这些突起增厚并沿角膜表面的长轴排列。角膜基质由原位间充质组织发育而来，并非从角膜缘间充质组织迁移而来。在发育早期，中央角膜变薄是由于晶状体对发育中的角膜的压迫。角膜的中央收缩使先前的观察者认为基质从周边角膜缘区域向角膜中心迁移。Descemet膜由角膜基质深层间充质细胞的突起发育而来。这些突起增厚并沿角膜后表面的长轴排列。该膜最初是细胞性的，细胞之间可见明确的间隔。随着成熟，Descemet膜变成均匀的结构。内皮来源于后基质的间充质细胞。这些细胞最初是立方形的，但随后变扁平。在角膜早期发育过程中，晶状体血管膜可能起重要作用。有人认为，前房早期由晶状体血管膜血管的渗出液维持。晶状体血管膜的血管被视杯前缘压向晶状体赤道。随着这个血管系统的退化，房水同时发育。房水产生的流体动力通过后推力作用辅助角膜塑形。与这种流体动力同时，角膜基质纤维在长度和宽度上增加。参与房水产生的结构，即睫状体上皮，以及房水引流结构，即滤角、小梁网和房水静脉，在晶状体血管膜退化的同时发育。限制和固定稳定部位在角膜缘，即直肌附着部位。在这些部位，随着角膜扩大出现凹陷。
