The cornea is the clear layer in front of the iris and pupil. It protects the iris and lens and helps focus light on the retina. It is composed of cells, protein, and fluid. The cornea looks fragile but is almost as stiff as a fingernail. However, it is very sensitive to touch.
Corneal disease or damage can cause pain, tearing, and decreased sharpness of vision (visual acuity). A slit lamp, which is an instrument that enables a doctor to examine the eye under high magnification, is usually used to examine the cornea (see Diagnosis of Eye Disorders: Slit-Lamp Examination). A doctor may apply eye drops that contain a dye called fluorescein, which temporarily stains areas of the cornea where cells are damaged, making these areas easier to identify.
Last full review/revision November 2012 by Melvin I. Roat, MD, FACS