I’m sure we’ve all heard the term corneal transplantation before, and we can always hear in the news about who has donated a cornea and successfully restored the sight of a patient with corneal lesions. However, do you really know where the cornea grows in the eye? And what about corneal transplants? Here’s what you need to know about corneas and corneal transplants. The thin cornea has five layers. The human eye is a very delicate structure, consisting mainly of the wall of the eye and its contents. As shown in the diagram, there are three layers around the periphery of the eye: the retina, the vascular pigment membrane, and the fibrous membrane from the inside out. Among them, the cornea and the sclera form the outer fibrous membrane: the cornea is a transparent membrane that lies on the surface of the black eye; the sclera is porcelain white, or what we call the white eye. If we compare the eye to a camera, the cornea is the lens. The cornea, which looks thin and transparent, can actually be divided into 5 layers, from outside to inside: epithelial cell layer, anterior elastic layer (also known as Bowman’s membrane), stromal layer, posterior elastic layer (also known as Descemet’s membrane), and endothelial cell layer. So, is it often said that a corneal transplant replaces all five of these layers? How is the transplant done, depending on the site of the lesion? Currently, the main types of corneal transplantation are penetrating corneal transplantation (total lamellar transplantation), lamellar corneal transplantation and corneal endothelial transplantation. The exact type of transplant used depends on which layer of the cornea is affected by the lesion. If the lesion advances from the front of the cornea, the epithelial layer is the first to be attacked. If the epithelial layer, the anterior elastic layer, or even the stromal layer all fall, all three layers are replaced, and this type of graft is called a lamellar graft. If the lesion breaches all layers of the cornea from front to back, all 5 layers are replaced, which is called a penetrating corneal graft. However, lesions are often very tricky, and most of them are wrapped from the back to the front, with the innermost endothelial layer being the first to suffer. In the past, for patients with damaged endothelial layers, even if the front layers were not diseased, the entire cornea had to be transplanted to achieve endothelial replacement. In recent years, a less invasive form of corneal transplantation, corneal endothelial transplantation, has gradually been developed. For patients with simple endothelial damage, instead of lifting the entire cornea for transplantation, a small incision is made at the edge of the cornea and the endothelial layer and posterior elastic layer (to which endothelial cells are attached) are transplanted, making it a “minimally invasive” form of corneal transplantation for patients.