Eye Anatomy

A guide to the many parts of the human eye and how they function.
The ability to see is dependent on the actions of several structures in and around the eyeball.
The graphic below lists many of the essential components of the eye's optical system.

When you look at an object, light rays are reflected from the object to the cornea, which is where the miracle begins. The light rays are bent, refracted and focused by the cornea, lens, and vitreous. The lens' job is to make sure the rays come to a sharp focus on the retina. The resulting image on the retina is upside-down.
Here at the retina, the light rays are converted to electrical impulses which are then transmitted through the optic nerve, to the brain, where the image is translated and perceived in an upright position!

Think of the eye as a camera. A camera needs a lens and a film to produce an image. In the same way, the eyeball needs a lens (cornea, crystalline lens, vitreous) to refract, or focus the light and a film (retina) on which to focus the rays. If any one or more of these components is not functioning correctly, the result is a poor picture. The retina represents the film in our camera.
It captures the image and sends it to the brain to be developed. The macula is the highly sensitive area of the retina.
The macula is responsible for our critical focusing vision. It is the part of the retina most used. We use our macula to read or to stare intently at an object.

Eyelids
The eyelids protect the eyes from the environment, injury and light. They maintain a smooth corneal surface by spreading tears evenly over the eye. The lids are composed of an outer layer of skin, a middle layer made of muscle and tissue that gives them form, and an inner layer of moist conjunctival tissue.

Pupil
The pupil is the black, circular opening in the center of the iris. It opens and closes in order to regulate the amount of light entering the eyeball.

Sclera
The sclera, commonly known as "the white of the eye," is the tough, opaque tissue that serves as the eye's protective outer coat.

Iris
The colored part of the eye is called the iris. It controls light levels inside the eye similar to the aperture on a camera. The round opening in the center of the iris is called the pupil. The iris is embedded with tiny muscles that dilate (widen) and constrict (narrow) the pupil size.

Cornea
The cornea is the transparent, dome-shaped window covering the front of the eye. It is a powerful refracting surface, providing 2/3 of the eye's focusing power. Like the crystal on a watch, it gives us a clear window to look through.

Lens
The purpose of the lens is to focus light onto the back of the eye. The nucleus, the innermost part of the lens is surrounded by softer material called the cortex. The lens is encased in a capsular-like bag and suspended within the eye by tiny guy wires called zonules.

Conjunctiva
The conjunctiva is the thin, transparent tissue that covers the outer surface of the eye. It begins at the outer edge of the cornea, covers the visible part of the eye, and lines the inside of the eyelids. It is nourished by tiny blood vessels that are nearly invisible to the naked eye.

Vitreous
The vitreous is a thick, transparent substance that fills the center of the eye. It is composed mainly of water and comprises about 2/3 of the eye's volume, giving it form and shape.

Choroids
The choroids lies between the retina and sclera. It is composed of layers of blood vessels that nourish the back of the eye.

Optic Nerve
The optic nerve transmits electrical impulses from the retina to the brain. It connects to the back of the eye near the macula. The visible portion of the optic nerve is called the optic disc.

The Macula
The macula is located roughly in the center of the retina, temporal to the optic nerve. It is a small and highly sensitive part of the retina responsible for detailed central vision. The fovea is the very center of the macula. The macula allows us to appreciate detail and perform tasks that require central vision such reading.

The Retina
The retina is a very thin layer of tissue that lines the inner part of the eye. It is responsible for capturing the light rays that enter the eye. Much like the film's role in photography. These light impulses are then sent to the brain for processing, via the optic nerve.