Corneal disease

Cornea
Schematic diagram of the human eye showing the cornea as separated from the sclera by the corneal limbus
Vertical section of human cornea from near the margin. (Waldeyer.) Magnified. Epithelium. Anterior elastic lamina. substantia propria. Posterior elastic lamina (Descemet's membrane). Endothelium of the anterior chamber. a. Oblique fibers in the anterior layer of the substantia propria. b. Lamellæ the fibers of which are cut across, producing a dotted appearance. c. Corneal corpuscles appearing in section. b. Lamellæ the fibers of which are cut longitudinally. d. Transition to the sclera, with more distinct fibrillation, and surmounted by a thicker epithelium. e. Small bloodvessels cut across near the margin of the cornea.
Identifiers
MeSH	D00331
Dorlands /Elsevier	c_55/12259559
TA	A15.2.02.012
FMA	58238
Anatomical terminology []

The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. The cornea, with the anterior chamber and lens, refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres. While the cornea contributes most of the eye's focusing power, its focus is fixed. The curvature of the lens, on the other hand, can be adjusted to "tune" the focus depending upon the object's distance. Medical terms related to the cornea often start with the prefix "" from the Greek word κέρας, horn.

The cornea has unmyelinated nerve endings sensitive to touch, temperature and chemicals; a touch of the cornea causes an involuntary reflex to close the eyelid. Because transparency is of prime importance, the cornea does not have blood vessels. Instead, oxygen dissolves in tears and then diffuses throughout the cornea to keep it healthy. Similarly, nutrients are transported via diffusion from the tear fluid through the outside surface and the aqueous humour through the inside surface, and also from neurotrophins supplied by nerve fibres that innervate it. In humans, the cornea has a diameter of about 11.5 mm and a thickness of 0.5–0.6 mm in the center and 0.6–0.8 mm at the periphery. Transparency, avascularity, the presence of immature resident immune cells, and immunologic privilege makes the cornea a very special tissue.