Have you seen your father’s wrist watch? It has clean, transparent glass over a dial where hour, minute hands are rotating. In a similar analogy, front surface of eye globe is fitted with transparent structure, which looks black, brown, grey, blue depending upon colour of tissue beneath it (i.e. Iris), this transparent structure is nothing but CORNEA. It adjusts rays of light entering the eye in a such a way that it falls exactly on retina. This meticulous work of focussing light rays is done by cornea which plays important role in perceiving clear picture of any object.
What is CORNEA?
Its transparent front layer of the eye. It is more or less spherical in shape and it covers iris (this structure gives colour to the eye like black, brown, grey, blue etc.), pupil (natural window of the iris) and anterior chamber of the eye.
Diameter of cornea: 11.5 mm
Thickness: central 550 microns & peripheral 800 microns
Cornea is made up of 6 layers:
2. Bowman’s membrane
4. Pre Descemet membranev
5. Descemet membrane
Cornea is transparent structure because of peculiar arrangement of its collagen fibres that lies in the stroma. It’s a structure without blood vessel, it derives nutrition from oxygen dissolved in tear & aqueous humor of anterior chamber. Endothelial layer has specialised pump which pumps out fluid from stroma of cornea which makes cornea pristine.
Role of Cornea :
1) Protective function: It has multiple nerve endings. Its most sensitive structure so when any object comes in contact with cornea, irritation occurs which sets up the reflex arc which causes blinking of eyes. This reflex prevents eye getting further exposed to irritant. Cornea also protects retina from UV light.
2) Visual function: It has very major role in bending light rays and tune them onto retina. Cornea is responsible for 2/3 rd. focussing power of the eye. Shape & curvature of cornea determines myopia / hypermetropia status of the eye.