The cornea or clear membrane is the transparent front part of the eye that covers the iris and pupil. When the cornea is touched, the eyelids will reflexively close. The cornea has no blood vessels. The contribution of the cornea apart from being a physical and chemical defense of the eyeball is also a component of a refractive media with a strength of 40-44 Diopters. The cornea has a curvature that varies from a small curvature (sloping) on the outer edge of the cornea and a large curvature (steep) in the center of the cornea, thus the cornea is able to refract light coming from outside to be passed through other refractive media components in the eyeball.
The cornea has a layer composed of surface ectoderm, namely epithelium, composed of neural crest cells, namely keratocytes and endothelial cells, supporting cells such as Langerhans cells (immunity), as well as numerous and thick acellular components in the stroma, Bowman and Descemet layers. The layers of the cornea successively from outside to inside are epithelium, Bowman, stroma, Descemet, endothelium. Among all the layers of the cornea, stroma makes up as much as 80-85% of the corneal layer and is composed of parallel fibers and collagens such as collagen types I, VI, and XII are covered by an extracellular matrix. The extracellular matrix is composed of collagen types I, III, V, VI, and glycosaminoglycans. The structure of this stroma is also unique because compared to other supporting tissues throughout the body, stromal collagen is arranged more densely and sticks tightly together, thus giving a clear and translucent macroscopic appearance of the cornea.