The Human Eye
This is the doctor's view of a typical human eye
The human eye is a small complex organ that is approximately .53 cu. in. (1in. wide by 1 in. tall by .9 in deep).
Eyes Components
The Cornea
The Cornea is the first part of the human eye to effect incoming light. Although the cornea's bending power is not as significant as that of the lens, its refractive properties do effect clear vision. Astigmatism is a common problem effecting humans who have a non-uniform curvature to the cornea causing distorted vision.
The Lens
The Lens serves as the fine tuning meduim for clear vision. It is aproximately 1 cm in diameter. The index of refraction of the lens changes as the lens is expanded or contracted by the Ciliary Body making it possible to focus on objects at a wide range of viewing distances. As humans age, the elasticity of the lens decreases as does the strength of the Ciliary Body. This causes the lens to stay a fixed shape making it possible to only see clearly at a fixed distance.
The Eye Ball
The interior of the eye has two fluid filled areas that are separated by the lens. The fluid in the smaller front area is called the Aqueous Humor and the jelly-like substance in the rear section is the Vitreous Humor. The regenerative Aqueous Humor is drained the Canal of Schlemm, which if blocked could cause the development of closed angle glaucoma.
The Iris
The iris is the colored part of the eye. The thickness and pigment of the tissue determines the color. The color of the eye is darker as the thickness of the tissue increases. The Iris is the system of muscles that expand and contract to regulate the pupil (the diaphram that allows light to enter the lens) of the human eye. The pupil can expand from approximately .2 cm up to .9 cm.
The Retina
The Retina is the light-sensitive region in the eye where images come into focus. The surface of the retina includes rod cells (primarily used for night or low-light vision) and cone cells (used to view color and detail). At the center of the retina is the Fovea which contains only cone cells and is responsible for viewing fine details clearly.