The eye is often considered the most important sensory organ of the human body. Seventy percent of our sensory cells are located on the retina with the muscles that control eye movement considered to be the most active muscles in the human body.
Light enters the eye through the anterior (or front) part of the eye where it passes first through the cornea and then lens which focus the light into a distinct beam. This light beam then moves through the middle of the eye and ends up on the back of the eye (retina) which is compsed of a light-sensitive membrane that translates the light into electrical signals which are, in turn, sent to the brain through the optical nerve (Figure 1).
The eye is composed of several distinct anatomical structures which include the cornea, lens, pupil, iris, aqueous humor, vitreous humor, sclera, choroid, zonule fibers and retina (Figure 1).
The cornea is the outermost transparent layer in the anterior part of the eye and is responsible for most of the focus or dioptric power. The curvature of the cornea determines how well the light is focused. After light leaves the cornea it passes through the lens which is flexible and can change shape to help you see at different distances (accommodation) (Figure 2).