In order to maintain good vision, the cornea (see section on Refractive Error and Ocular Anatomy) must remain crystal clear. Because it is under pressure, the fluid within the eye is constantly being forced into the cornea, which absorbs it like a sponge. A special layer of cells lines the inside of the cornea, serving to pump the fluid back into the eye, maintaining the cornea’s clarity. These cells are known as the corneal endothelium.
With age, or sometimes due to injury or other cause, these endothelial pump cells start to die. During an ocular examination, an eye doctor may notice guttae, small areas of abnormal material where the endothelial cells have been lost. It is common to see a few guttae in middle-aged and older individuals- up to 70% of people over 40 have them.