The eye works like a camera.
The light rays of the image enter the eye through the cornea, a clear window similar to a lens filter, which provides most of the focusing power of the eye.
The cornea is composed of several layers of tissue.
The outer layer or epithelium is the eye’s protective layer. This layer is made up of cells that have the ability to grow back within five to seven days, and therefore, allow for fast healing of superficial injuries. Most of the inner layers provide strength to the eye.
The middle inner layer, the stroma, is the largest layer and the part of the cornea that is typically modified in refractive surgery to change the focus. Damage to this layer and posterior in the cornea will result in corneal scarring.
The last layer is the endothelium, a very important layer that is largely responsible for keeping the cornea clear by regulating solute transport.