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The Normal Eye

The human eye is truly amazing. It focuses light to form images or "pictures" at the back of your eye, much like a camera. The eye instantly changes these images into electrical signals and sends them to your brain. The brain interprets the signals and you experience "seeing". The eye accommodates to changing lighting conditions and focuses rays of light originating from various distances.

Basic Structures

Cornea: This clear outer lens provides two-thirds of the focusing power of the eye. The cornea is made up of transparent tissue, which allows light to pass through. The cornea focuses the light by bending it so the light rays form an image on the retina. Since the cornea has the greatest bending (focusing) power, it is the cornea's shape that determines a great deal of quality of your vision.

Iris & Pupil: The colored part of the eye is called the iris and functions much like the iris of a camera, opening and closing, to control the amount of light entering through the pupil (that dark opening in the center the iris).

Crystalline lens: The crystalline lens is located behind the iris and provides one third of the focusing power of the eye. The crystalline lens works to further bend light rays as they pass through the eye to form an image on the retina.

Retina: Located in the lining at the back of the eye, the retina acts as an electrical system to send impulses to your brain via the optic nerve. The retina contains photoreceptor cells that collect information from light as it passes through the cornea and crystalline lens to the back of the eye. Your brain interprets the retina's electrical response into what you to experience as images.

Fovea: The focal point at the center of the retina is called the fovea. Light focused here produces the sharpest vision.