the eye

Light rays enter the eye through the cornea, the clear front “window” of the eye. The cornea’s refractive power bends the light rays in such a way that they pass freely through the pupil the opening in the centre of the iris through which light enters the eye. 

The iris works like a shutter in a camera. It’s got the ability to enlarge and shrink, depending on how much light is entering the eye. After passing through the iris, the light rays pass thru the eye’s natural crystalline lens. This clear, flexible structure works like the lens in a camera, shortening and lengthening its width in order to focus light rays properly.

Light rays pass through a dense, transparent gel-like substance, called the vitreous that fills the globe of the eyeball and helps the eye hold its spherical shape. In a normal eye, the light rays come to a sharp focusing point on the retina. The retina functions much like the film in a camera.

It is responsible for capturing all the light rays, processing them into light impulses through millions of tiny nerve endings, then sending these light impulses through over a million nerve fibres to the optic nerve. Because the keratoconus cornea is irregular, and cone shaped, light rays enter the eye at different angles, and do not focus on one point the retina, but on many different points causing a blurred, distorted image. In summary, the cornea is the clear, transparent front covering which admits light and begins the refractive process. It also keeps foreign particles from entering the eye.

CORNEAL LAYERS

-Although appearing to be one clear membrane, the cornea is composed of five distinct layers of tissue, each with its own function.

-Epithelium is the thin outermost layer of fast-growing and easily-regenerated cells.

-Bowman’s layer consists of irregularly-arranged collagen fibres and protects the corneal stroma. It is 8 to 14 microns thick.

-Stroma, the transparent middle and thickest layer of the cornea is made up of regularly-arranged collagen fibres and keratocytes (specialized cells that secrete the collagen and proteoglycans needed to maintain the clarity and curvature of the cornea)

-Descemet’s membrane is a thin layer that serves as the modified basement membrane of the corneal endothelium.

-Endothelium is a single layer of cells responsible for maintaining proper fluid balance between the aqueous and corneal stromal compartments keeping the cornea transparent

THE CORNEA

-The eye is enclosed by a tough white sac, the sclera. The cornea is the transparent window in this white sac which allows the objects you are looking at to be carried in the form of light waves into the interior of the eye.

-The surface of the cornea is where light begins its journey into the eye. The cornea’s mission is to gather and focus visual images. Because it is out front, like the windshield of an automobile, it is subject to considerable abuse from the outside world.

-The cornea is masterfully engineered so that only the most expensive manmade lenses can match its precision. The smoothness and shape of the cornea, as well as its transparency, is vitally important to the proper functioning of the eye. If either the surface smoothness or the clarity of the cornea suffers, vision will be disrupted.

In keratoconus, the irregular shape of the cornea does not allow it to do its job correctly, leading to distortion of the image it passed to the retina and transmitted to the brain.