The cornea is a sheet of tissue made up of five layers: epithelium, Bowman's membrane, stroma, Descemet's membrane, and endothelium. The epithelium is the outermost layer. It is a squamous stratified epithelium that contains many nervous fibers, is highly sensory, and has a high regenerative capacity. The epithelium is continuous with the epithelium of the conjunctiva. The Bowman's membrane is located under the epithelium, and it is not found in all vertebrates. It consists of many collagen fibers but lacks elastic fibers. The stroma lies under the Bowman's membrane. It is the thicker layer, comprising up to 90% of the corneal thickness. The stroma is connective tissue, mostly collagen types I and IV organized in layers and showing different arrangements in each layer. Chondroitin sulfate and keratan sulfate are abundant in this layer. Some errant lymphocytes and fibroblasts can also be present. The Descemet's membrane follows the stroma. It is the basal lamina of the endothelium, the innermost layer of the cornea. The endothelium is the layer forming the wall of the eye's anterior chamber. The cornea continues laterally with the sclera through a transitional zone called the limbus.
